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Programming with lcc-win

1. s 115 26 40 25 jC A SBS 1 108 20 g 103 18 F 70 17 q 113 16 6i is Ce 6S Ts h 104 12 A 65 I d 100 11 po AA S l EC 91 10 1 93 10 42 10 34 10 123 9 2 50 9 p 112 9 125 9 1 49 8 46 8 y 121 8 43 8 S 83 7 R 82 7 H 72 7 gt 62 6 lt 60 6 DE B7 5 m 109 5 v 118 5 0O 48 5 K ay SA 4 Soi Sa 92 4 V 86 4 6 54 4 45 3 x 120 3 b 98 3 Boy 3 tA Tey 203 hap Boy 2 9 58 2 C 35yr Se U 85 2 Et 69 2 A acy E Te a w 119 1 O 79 S41 2 G22 S41 8 Si S49 C 78 1 We see immediately that the most frequent character is the space with a count of 154 followed by the letter e with a count of 77 then n with 60 etc 6699 Strange where does z appear Ah yes in sizeof And that I Ah in FILE ok seems to be working 1 21 1 Fine points of structure use 1 When you have a pointer to a structure and you want to access a member of it you should use the syntax pointer gt field 2 When you have a structure OBJECT not a pointer you should use the syntax object field Beginners easily confuse this 3 When you have an array of structures you index it using the normal array notation syntax then use the object or the pointer in the arra
2. pLogPal gt pal lpLogPal gt pal Version 0x300 NumEntries 256 Copy the current system palette into the logical palette GetSystemPaletteEntries hDC 0 256 Create the palette hPal CreatePalette lpLogPal LPPALETTEENTRY lpLogPal gt palPalEntry Clean up GlobalFree lp e ogPal ReleaseDC NULL hDC return hPal eate24BPPDIBSection HDC hDC int iWidth int iHeight bmi hbm I Create a 24 bit per pixel surface i HBITMAP Cr BITMAP INFO HBITMAP LPBYTE Initialize ZeroMemory amp b pBits to Os mi sizeof bmi the header biSize sizeof BITMAPINFOHEADER biWidth iWidth biHeight iHeight biPlanes 1 biBitCount 24 biCompression BI_RGB Create the surface CreateDIBSection hDC amp bmi DIB RGB COLORS amp pBits NULL 0 Initialize bmi bmiHeader bmi bmiHeader bmi bmiHeader bmi bmiHeader bmi bmiHeader bmi bmiHeader hbm return hbm Some Coding Tips Print the entire contents including the non client area of the specified window to the default printer BOOL PrintWindowToDC HWND hWnd HBITMAP hbm HDC hdcPrinter HDC hdcMemory HDC hdcWindow int iWidth int iHeight DOCINFO di RECT ECF DIBSECTION ds HPALETTE hPal Do we have a valid window if IsWi
3. This is much clearer We put the code for handling the entry field messages in its own proce dure EntryFieldMessages Its code is int EntryFieldMessages HWND hDlg WPARAM wParam HWND hIdOk GetDligItem hDlg IDOK switch HIWORD wParam case EN_CHANGE if GetDlgItemText hDlg IDENTRYFIELD buffer sizeof buffer There is some text in the entry field Enable the IDOK button EnableWindow hIdOk 1 else no text disable the IDOK button EnableWindow hIdok 0 break return 1 Let s look at this more in detail Our switch statement uses the HIWORD of the first message parameter This message carries different information in the upper 16 bits the HIWORD than in the lower 16 bits LOWORD In the lower part of wParam we find the ID of the control that sent the message in this case IDENTRYFIELD and in the higher 16 bits we find which sub message of WM_COMMAND the control is sending to us in this case EN_CHANGE 9 i e a change in the text of the edit field There are many other notifications this small window is sending to us When the user leaves the edit field and sets the focus with the mouse somewhere else we are notified etc But all of those notifications follow the same pattern they are sub messages of WM_COMMAND and their code is sent in the upper 16 bits of the wParam message parameter Continuing the analysis of EntryFieldMe
4. We loop through all sibling windows calling ourselves recursively with the child windows In our loop we do We get the text of the window to show it in our tree We do this by sending the WW_GETTEXT message to the window We get the class name of the window We format the text enclosed in quotes and the class name in a buffer We start filling the TV_INSERTSTRUCT These steps are very similar to what we did for the desktop window After inserting our node in the tree we ask if this window has child windows If it has we call Scan recursively with the new node and the new child window Then we ask if this window has sibling windows If it has the main loop will go on since GetWindow will give us a non null window handle If it hasn t we are done and we exit 2 10 6 Review Let s look at our BuildTree function again and ask us How could this fail We notice immediately several things We always add items to the tree at the end but we never cleanup the tree control This means that after a few times the user has clicked in the menu we will have several times all the win dows of the system in our tree All nodes should be deleted when we start The tree control will redraw itself several times when we add items This is unnecessary and produces a disturbing blinking in the display We should hold the window without any redraw ing until all changes are done and then redraw once at the end We modify th
5. 0 0 Rect right Rect left Assume a rectangle structure Rect bottom Rect top that contains the coordinates hParentWnd HMENU 14376 Window identifier hInst Application instance NULL The controls edit listbox and others are already predefined when windows starts You can use them at any time Some others however are NOT like that and you need to call the API InitCommonControlsEx before you can use them A more complex example a clone of spy exe 273 2 10 A more complex example a clone of spy exe What can we do with the empty window that Wedit generates Let s do a more difficult problem We want to find out all the windows that are opened at a given time in the system We will display those windows in a tree control since the child win dows give naturally a tree structure When the user clicks in a window label the program should display some information about the window in the status bar We generate a skeleton with Wedit as described above We create a new project and generate a simple single window application 2 10 1 Creating the child windows OK Now we come back to the task at hand The first thing to do is to create the tree control window A good place to do these kinds of window creations is to use the opportunity the sys tem gives to us when it sends the WM_CREATE message to the main window We go to the procedure for the main window called MainWn
6. Each DC must select a bitmap object to store pixel data bmBackOld SelectObject hdcBack bmAndBack bmObjectOld SelectObject hdcObject bmAndOb ject bmMemO1d SelectObject hdcMem bmAndMem bmSaveOld SelectObject hdcSave bmSave Set proper mapping mode SetMapMode hdcTemp GetMapMode hdc Save the bitmap sent here because it will be overwritten BitBlt hdcSave 0 0 ptSize x ptSize y hdcTemp 0 0 SRCCOPY Set the background color of the source DC to the color contained in the parts of the bitmap that should be transparent cColor SetBkColor hdcTemp cTransparentColor Create the object mask for the bitmap by performing a BitBlt from the source bitmap to a monochrome bitmap BitBlt hdcObject 0 0 ptSize x ptSize y hdcTemp 0 0 SRCCOPY Set the background color of the source DC back to the original color SetBkColor hdcTemp cColor Create the inverse of the object mask BitBlt hdcBack 0 0 ptSize x ptSize y hdcObject 0 0 NOTSRCCOPY Copy the background of the main DC to the destination BitBlt hdcMem 0 0 ptSize x ptSize y hdc xStart yStart SRCCOPY Mask out the places where the bitmap will be placed BitBlt hdcMem 0 0 ptSize x ptSize y hdcObject 0 0 SRCAND Mask out the transparent colored pixels on the bitmap BitBlt hdcTemp 0 0 ptSize x ptSize y hdcBack 0 0 SRCAND XOR the bitmap with the
7. Hiding the gibberish in a typedef is quite useful in this situations and much more readable later 2 6 2 Event oriented programming In another level what those programs show us is how to do event oriented programs i e pro grams designed to react to a series of events furnished by the event stream Under windows each program should make this event stream pump turn by writing some where while GetMessage ProcessMessage we will describe the exact syntax later 7 This message pump is hidden now from view under the DefDlgProc procedure but it is the source of all the messages passed to the dialog proce dure that we defined A windows program is designed to react to those messages or events It will process them in sequence until it decides to stop the message pump ending the program The general structure is then 117 Application frameworks like MFC introduce an additional simplifying layer between you and the operating system Much has been said and written about them and here I will not discuss this in much more detail Suffice to note that the purpose of Icc win is to let you be always in control of what is going on You can do here anything contrary to a framework where you can only do what the framework provides for and nothing else True an application framework can simplify the coding and many people use them It would be feasible to build such a framework with Icc win but I will le
8. el n n achBuff 0 0O Add each value to a list box The Registry 311 if lstrlen achValue lstrcpy achValue lt NO NAME gt wsprintf achBuff Sd s j achValue SendMessage GetDlgItem hDlg IDL_LISTBOX2 LB_ADDSTRING 0 LONG achBuff SetCursor LoadCursor NULL IDC_ARROW 2 16 3 Rules for using the registry Although there are few technical limits to the type and size of data an application can store in the registry certain practical guidelines exist to promote system efficiency An application should store configuration and initialization data in the registry and store other kinds of data elsewhere Generally data consisting of more than one or two kilobytes K should be stored as a file and referred to by using a key in the registry rather than being stored as a value Instead of dupli cating large pieces of data in the registry an application should save the data as a file and refer to the file Executable binary code should never be stored in the registry For instance lcc win stores just the name of the path to the Icc installation directory in the registry and all other data is stored in files in the Icc lib directory This saves registry space A value entry uses much less registry space than a key To save space an application should group similar data together as a structure and store the structure as a value rather than storing each of the structure members as
9. strcpy newlist gt Name name if sta rt newlist gt Next return newlist Parse command line TCHAR argv start TCHAR envp building list of file names Switches can come in any order FILELIST for int if argv i 0 x files i 1 i lt argc NULL i argv i 0 switch tolower argv i 1 case case bDisplayOnly TRUE case cas cas hears bQuiet TRUI brea Fl Ky nh break other bPrompt TRU brea e z bZap TRUI break e help return 0 Fl Ky Fl default else fil if files usage return 0 Got a file name es AddToLi NULL Make it absolute and add to st files MakeAbsolute argv i list No fil usage return 0 s specified tell bozo user how to use this command Delet int nDel loop EOF 3 Fil cycle 0 all the files in the list over list of files and recycle each one es files Onl EAN Fi it fil fil s gt Next e exists y recycle bQuiet amp amp tell user eexists files gt Name bPrompt I m recycling this file 376 C Tutorial fprintf stderr s s n bZap Deleting Recycling files gt Name if bDisplayOnly if bPrompt confirm files gt Name
10. Finally Recycle the file Use CRecycleFil int err Recycle files gt Name bZap if err 0 nDel t else Can t recycle display error message fprintf stderr Error d Ss err GetErrorMsg err else fprintf stderr File not found s n files gt Name if bQuiet fprintf stderr d files recycled n nDel return 0 void usage void printf Usage RECYCLE QNPZ file n void help void printf Purpose Send one or more files to the recycle bin n printf Format RECYCLE Q N P Z file n printf Q uiet no messages n printf N othing don t delete just show files n printf P rompt confirm each file n printf Z ap really deletesame as del n Make a file name absolute with respect to current directory char MakeAbsolute char relname Get current directory char cwd GetCurrentDir char absname if relname 0 amp amp relname 1 amp amp relname 1 relname is already absolute absname relname else if relname 0 relname begins with add drive letter and colon memmove relname 2 relname strlen relname 1 relname 0 cwd 0 relname 1 cwd 1l absname relname FAQ 377 else file name begins with letter relname begins with a letter prepend cwd strcat cwd relname absname cw
11. 32 957 E 33 2 34 10 35 2 6 37 95 wal B9Yy S13 40 18 41 18 42 2 43 6 44 7 46 2 47 2 O 48 4 1 49 4 2 50 3 3 51 1 4 52 1 5a 53 2 6 54 2 58 I 7 59 19 lt 60 5 61 11 gt 62 4 A 65 1 E 69 2 F 70 7 I 73 1 LE 76 3 N 78 1 OC FO 1 U 85 2 91 7 92 4 93 7 a 97 12 b 98 2 Gul 99 33 da 100 8 e 101 38 f 102 23 g 103 8 h 104 6 i 105 43 1 108 14 m 109 2 n 110 43 o 111 17 p 112 5 gq CILI r 114 23 s 115 14 t 116 29 u 117 19 v 118 3 w 119 1 x 120 3 y 121 1 123 6 125 6 What is missing obviously is to print the table in a sorted way so that the most frequent char acters would be printed first This would make inspecting the table for the most frequent char acter easier 1 18 1 How to sort arrays We have in the standard library the function qsort that sorts an array We study its prototype first to see how we should use it 58 void qsort void b size_ t n size_t s int f const void Well this is quite an impressing prototype really But if we want to learn C we will have to read this as it was normal prose So let s begin from left to right 58 The prototype is in the header file stdlib h Using arrays and s
12. LRESULT HandleWmNotify HWND hwnd WPARAM wParam LPARAM lParam NMHDR nmhdr V_HITTESTINFO testInfo HWND hTree GetDlgItem hwnd IDTREEWINDOW HTREEITEM hti HWND hwndStart nmhdr NMHDR 1Param switch nmhdr gt code case NM_CLICK memset amp testInfo 0 sizeof TV_HITTESTINFO GetCursorPos amp testInfo pt MapWindowPoints HWND_DESKTOP hTree amp testInfo pt 1 hti TreeView_HitTest hTree amp testInfo if hti HTREEITEM 0 break hwndStart GetTreeItemInfo hTree hti SetTextInStatusBar hwnd hwndStart break return DefWindowProc hwnd WM_NOTIFY wParam lParam We just handle the NM_CLICK special case of all the possible notifications that this very com plex control can send We use the NMHDR part of the message information that is passed to us with this message in the Param message parameter Our purpose here is to first know if the user has clicked in an item or somewhere in the back ground of the tree control We should only answer when there is actually an item under the coordinates where the user has clicked The algorithm then is like this Get the mouse position Since windows has just sent a click message the speed of current machines is largely enough to be sure that the mouse hasn t moved at all between the time that windows sent the message and the time we process it Besides whe
13. S3c 4d d n count count Frequencies count return 0 We declare an array of 256 integers numbered from zero to 255 Note that in C the index ori gin is always zero This array is not enclosed in any scope Its scope then is global i e this identifier will be associated to the integer array for the current translation unit the current file and its includes from the point of its declaration on Since we haven t specified otherwise this identifier will be exported from the current module and will be visible from other modules In another compilation unit we can then declare extern int Frequencies and we can access this array This can be good it allow us to share data between modules or it can be bad it allows other modules to tamper with private data it depends on the point of view and the application oF If we wanted to keep this array local to the current compilation unit we would have written static int Frequencies 256 The static keyword indicates to the compiler that this identifier should not be made visible in another module The first thing our program does is to open the file with the name passed as a parameter This is done using the fopen library function If the file exists and we are able to read from it the library function will return a pointer to a FILE structure defined in stdio h If the file can t be opened it returns NULL We test for this condition
14. What is interesting about this solution is that we use no intermediate memory to hold the results If we have a lot of files the size of the resulting list or table would be significant If an application doesn t need this it doesn t have to pay for the extra overhead Using the name of the file the callback function can query any property of the file like the date of creation the size the owner etc Since the user writes that function there is no need to give several options to filter that information One of the big advantages of C is its ability of using function pointers as first class objects that can be passed around and used as input for other procedures Without this feature this appli cation would have been difficult to write and would be a lot less flexible Note too that any error in the function pointer argument will provoke a crash since we do not test for the validity of the received function pointer But let s be clear the biggest drawback is that the user has to write a function in C Imagine telling your friends that before they use your program they just write a function in C compile it link it with your stuff etc Let s examine how we put function pointers to good use assume the following Problem Write a program to print all numbers from 1 to n where n integer gt 0 without using any control flow statements switch if goto while for etc Numbers can be written in any order Solution The
15. 336 C Tutorial PERR bSuccess GetConsoleScreenBufferiInfo dwConSize csbi dwSize X csbi dwSize yY fill the entire screen with blanks bSuccess FillConsoleOutputCharacter hConsole TCHAR dwConSize coordScreen amp cCharsWritten PERR bSuccess FillConsoleOutputCharacter get the current text attribute bSuccess GetConsoleScreenBufferInfo hConsole amp csbi PERR bSuccess ConsoleScreenBufferiInfo now set the buffer s attributes accordingly bSuccess FillConsoleOutputAttribute hConsole csbi wAttributes dwConSize coordScreen amp cCharsWritten ERR bSuccess FillConsoleOutputAttribute put the cursor at 0 0 tg bSuccess SetConsoleCursorPosition hConsole coordScreen PERR bSuccess SetConsoleCursorPosition return This function can be called like this cls Get StdHandle STD_OUTPUT_HANDLE i The library TCCONIO LIB contains many other functions for text manipulation using the console interface The corresponding header file is TCCONIO H which is automatically included when you include conio h This library was contributed by Daniel Guerrero daguer geocities com 2 21 4 Getting a pointer to the stack To get a pointer to the stack use the following code far MyFunction int x int far y amp x NOTE This pointer will not be valid when the function is exited since the s
16. define FE_TONEAREST 0 define FE_DOWNWARD 1 define FE_UPWARD 2 define FE_TOWARDZERO 3 You can change the default rounding precision by using the function fesetround int also declared in the same header file The rationale for this rounding modes is the following To know if an algorithm is stable change your rounding mode using the same data and run your program in all rounding modes Numerical programming 201 Are the results the same If yes your program is numerically stable If not you got a big prob lem and you will have to debug your algorithm For a total of N floating point operations you will have a rounding error of 87 1 For round to nearest is sqrt N machine epsilon 2 For round up is N machine epsilon 3 For round down is N machine epsilon 4 For round to zero is N machine epsilon if the number is positive N Machine Epsilon if the number is negative The number you actually obtain will depend of the sequence of the operations 1 37 2 5 The machine epsilon The standard defines for each floating point representation float double long double the dif ference between 1 and the least value greater than 1 that is representable in the given floating point type In IEEE754 representation this number has an exponent value of the bias mantissa bits and a mantissa of zero For double precision this means sign 0 exponent Another way to define this quantity in terms of the mathematical
17. We need to include windows h for getting the prototypes of LoadLibrary and GetProcAd dress besides some constants like INVALID _HANDLE_VALUE stdio h is necessary too since we use fprintf This is a function pointer called pfnGetString that points to a function that returns an int and takes a char another char and an int as arguments If you do not like this syntax please bear with me Even Dennis Ritchie says this syntax isn t really the best one We store in our dllHandle the result of calling LoadLibrary with an absolute path so it will always work at least in this machine Note that the backslashes must be repeated within a character string 256 C Tutorial We test if the handle received is a correct one If not we put up some message and we exit the program We are now ready to assign our function pointer We must cast the return value of GetProcAd dress to a function like the one we want The first part of the statement is just a cast using the same construction that the declaration of the function pointer before with the exception that we do not include the identifier of course since this is a cast But the arguments to Get Pro cAddress are weird We do not pass really the name of the function Get String but a name _GetString 12 Where does this name come from The rest of the program stays the same To understand where this weird name comes from we have to keep in mind the following facts
18. amp i the result is a pointer to the given object Access the contents at the machine address stored in pointer bog og ie pData the pointer See Indirection on page 71 expression Subtract expression from zero i e change the sign a Bitwise complement expression Change all 1 bits to expression E 0 and all 0 bits to 1 Negate expression if expression is zero expression expression becomes one if expression is different than zero it la becomes zero sizeof expr Return the size in bytes of expr see Sizeof on page 59 sizeof a Change the type of expression to the given type This is called a cast The expression can be a Pee SSP literal expression enclosed in braces as in a structure ee initialization See page 68 expr expr Multiply a b expr expr Divide a b expr expr Divide first by second and return the remainder a b expr expr Add a b exprl expr2 Subtract expr2 from expr1 a b exprl lt lt expr2 Shift left expr1 expr2 bits a lt lt b exprl gt gt expr2 Shift right expr1 expr2 bits a Soop exprl lt expr2 1 if expr1 is smaller than expr2 zero otherwise a lt b EEE AE 1 if expr1 is smaller or equal than expr2 zero E otherwise 42 C programming with Icc win32 1 if expr1 is greater or equal than expr2 zero 1 gt 2 expr expr tin
19. source err error code 0 language ID buf buffer to receiv BUFSIZ size of buf NULL arguments return buf endif messag 2 22 27 Making a timed message box One of the problems with the MessageBox API is that it will stop everything requiring that the user clicks in the OK button There are many situations where this is not desirable since it makes automated program running a problem Here is a solution proposed in the knowledge base of MSDN void CALLBACK MessageBoxTimer HWND hwnd UINT uiMsg PostQuitMessage 0 UINT idEvent DWORD dwTime KOR KKK KK KK I k kkk k kkk k A k k k k k k k k k k k k k k k k k k k k k k kk k I kkk k kk k k k TimedMessageBox a timeout specified timeout The same as the standard MessageBox xcept it also accepts If the user does not respond within the then the value 0 is returned instead of one of the ID values KK RA I A A A A I I I I UINT TimedMessageBox HWND hwndParent LPCTSTR ptszMessage LPCTSTR ptszTitle UINT flags DWORD dwTimeout UINT idTimer UINT uiResult MSG msg idTimer SetTimer NULL 0 dwTimeout Set a timer to dismiss the message box TIMERPROC MessageBoxTimer uiResult MessageBox hwndParent ptszMessage ptszTitle flags Finished with the timer X KillTimer NULL idTimer See if there is a WM_QUIT message in the queue If so then you timed out
20. allocate the buffers and try the call again PdhEnum functions will return ERROR SUCCESS in WIN2K but PDH_MORE_DATA in XP and later In either case dwCounterListSize and dwinstanceListSize should contain the correct buffer size needed II szCounterListBuffer szInstanceListBuffer szCounterListBuffer if LPTSTR mall LPTSTR malloc dwInstanceListSize oc dwCounterListSize NULL 348 C Tutorial szInstanceListBuffer NULL printf nUnable to allocate buffers return 1 pdhStatus PdhEnumObjectItems NULL reserved NULL local machine Process object to enumerate szCounterListBuffer pass in NULL buffers amp dwCounterListSize an 0 length to get szInstanceListBuffer required size amp dwinstanceListSize of the buffers in chars PERF_DETAIL WIZARD counter detail level 0 if pdhStatus ERROR_SUCCESS printf nRunning Processes walk the return instance list for szThisInstance szInstanceListBuffer szThisInstance 0 szThisInstance strlen szThisInstance 1 printf n amp s szThisInstance if szCounterListBuffer NULL free szCounterListBuffer if szInstanceListBuffer NULL free szInstanceListBuffer return 0 2 21 24 Changing a File Time to the Current Time The following example sets the last write time for a file to the current system time using the SetFileTime fu
21. int const constant_ptr The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer but ptr_to_constant itself may be changed to point to another object Simi larly the contents of the int pointed to by constant_ptr may be modified but constant_ptr itself shall always point to the same location 1 13 18 1 Implementation details Lcec win considers that when you declare static const int myVar 56 it is allowed to replace everywhere in your code the variable my Var with 56 1 13 19 Goto This statement transfers control to the given label Many scientific papers have been written about this feature and many people will tell you that writing a goto statement is a sin I am agnostic If you need to use it use it Only do not abuse it Note that labels are associated with statements You can t write if condition if another _condition goto lab lab WRONG In this case the label is not associated with any statement this is an error You can correct this by just adding an empty statement if condition if another_condition goto lab lab empty statement Now the label is associated with a statement A goto statement can jump in the middle of a block skipping the initialization of local vari ables This is a very bad idea For instance if condition goto label int m 0 A closer view 61 label In this case the jump will ski
22. minus will cast any type shorter than an int into a signed int If the type is larger than an integer it will be left unchanged 1 3 16 Octal numbers Remember that numbers beginning with zero are treated as number written in base 8 The number 012 is decimal 10 not 12 This error is difficult to find because everything will com pile without any error after all this is a legal construct 1 3 17 Wrong assumptions with realloc Consider this code if req gt len realloc p len memcpy p mem len This code assumes that the block p will be reallocated to the same address what can be false The correct way of doing this reallocation is if req gt len p realloc p len memcpy p mem len This is still wrong since it assumes that realloc always returns the desired memory block But in reality realloc could very well fail and that should be tested if req gt len void tmp realloc p len if tmp p tmp else fatal_error No more memory n memcpy p mem len We suppose that the function fatal_error never returns 1 3 18 Be careful with overflow Consider this code include lt stdint h gt include lt stdio h gt include lt stdlib h gt define SIZE_MAX Oxffffffff int main size_t s n void p 222 C programming with Icc win32 s 12 SIZE_MAX s 1 5 li P malloc s n printf s lu n lu s n lu p p n s n n s p We
23. return at1 Then int a b f c will be equivalent to writing int a bt1 ct1 Note that this expansion is realized in the lcc win compiler only when optimizations are ON In a normal debug setting the inline keyword is ignored You can control this behavior also by using the command line option fno inline 1 13 29 Logical operators A logical expression consists of two boolean expressions i e expressions that are either true or false separated by one of the logical operators amp amp AND or or The AND operator evaluates from left to right If any of the expressions is zero the evaluation stops with a FALSE result and the rest of the expressions is not evaluated The result of several AND expressions is true if and only if all the expressions evaluate to TRUE Example 1 amp amp 1 amp amp 0 amp amp 1 amp amp 1 66 C programming with Icc win32 Here evaluation stops after the third expression yields false zero The fourth and fifth expres sions are not evaluated The result of all the AND expressions is zero The OR operator evaluates from left to right If any of the expressions yields TRUE evalua tion stops with a TRUE result and the rest of the expressions is not evaluated The result of several OR expressions is true if and only if one of the expressions evaluates to TRUE If we have the expression result exprl amp amp expr2 this is equivalent to the followin
24. 3 We call the ftell function to retrieve the current position Note that that function returns 1 if there was an error We do not test for this result since if that function failed we return the error code without any further processing 4 Since all this functions return a 32 bit integer files bigger than 2GB can t be measured using this functions Icc win provides some 64 bit file primitives and the Windows operating system provides a full set of 64 bit file primitives 1 9 5 File buffering A file can be either unbuffered all characters and input output operations happen immedi ately or buffered meaning that characters are accumulated in a buffer and transmitted from or to the device as a block Obviously buffering input output has the advantage of efficiency since fewer i o operations are performed Buffering can be either fully buffered when i o is done when the buffer is full only or line buffered when i o is done only when the new line character is found in the data Normally the files associated with the keyboard and the screen are line buffered and disk files are fully buffered You can force the system to empty the buffer with the function fflush The amount of buffering can be changed with the setbuf and setvbuf functions The setbuf function allows you to setup your own buffer instead of the default one This can be sometimes better when you know you need to read write large chunks of the file for instanc
25. The volatile keyword means that the object qualified in this way can change by means not known to the program and that it must be treated specially by the compiler The compiler should follow strictly the rules of the language and no optimizations are allowed for this object This means that the object should be stored in memory for instance and not in a regis ter This keyword is useful for describing a variable that is shared by several threads or pro cesses A static volatile object is a good model for a memory mapped I O register i e a memory location that is used to read data coming from an external source 1 6 8 Casting The programmer can at any time change the type associated with a piece of data by making a cast operation For instance if you have float f 67 8f you can do double d double f Types 19 The double means that the data in f should be converted into an equivalent data using the double precision representation We will come back to types when we speak again about casts later page 68 1 6 9 The basic types The implementation of the C language by the Icc win compiler has the following types built in All this types are part of the standard ANSI C language With the exception of the _Complex type they should appear in most C implementations and they do appear in all win dows compilers 74 Type Size Description bytes Bool bool 1 Logical type
26. entry point the above mentioned main procedure in C or other procedure that is used as the entry point The static data of the program i e the string literals the numbers or tables that are known when the program starts This data area con be further divided into an initialized data section or just empty reserved space that is initialized by the operating system to zero when the program is loaded 8 There is no way to import selectively some identifiers from another included file Either you import all of it or none Hello 3 The body is a series of expressions separated by semicolons Each statement can be an arith metic operation an assignment a function call or a compound statement i e a statement that contains another set of statements 1 3 Hello To give you an idea of the flavor of C we use the famous example given already by the authors of the language We build here a program that when invoked will put in the screen the mes sage hello Note that obviously the numbers in parentheses are not part of the program text but are in there so that I can refer to each line of the program include lt stdio h gt 1 int main void 2 3 printf Hello n 4 return 0 5 6 1 Using a feature of the compiler called pre processor you can textually include a whole file of C source with the include directive In this example we include from the standard includes of the compiler
27. i is invalid This one is invalid too i i i in clear i i 1 3 6 Unexpected Operator Precedence The code fragment if chr getc EOF printf The value of chr is d n chr will always print 1 as long as end of file is not detected in getc The intention was to assign the value from getc to chr then to test the value against EOF The problem occurs in the first line which says to call the library function getc The return value from getc an integer value representing a character or EOF if end of file is detected is compared against EOF and if they are not equal it s not end of file then 1 is assigned to the object chr Otherwise they are equal and 0 is assigned to chr The value of chr is therefore always 0 or 1 The correct way to write this code fragment is if chr getc EOF printf The value of chr is d n chr The extra parentheses force the assignment to occur first and then the comparison for equality is done Another operator precedence error is the following include stdio h 93 Doing assignment inside the controlling expression of loop or selection statements is not a good programming practice These expressions tend to be difficult to read and problems such as using instead of are more difficult to detect when in some cases is desired 94 How does it work He tests first if the lower 16 bits contain a 1 bit The number 6
28. specifying a timer procedure and a 5 000 millisecond interval between timer ticks e In the timer procedure call SetCaretBlinkTime 10000 This resets the timer in Windows that controls the caret blink When an application implements this procedure Windows never removes the caret from the screen and the caret does not blink 2 22 12 How do I create a title window splash screen A splash screen title screen can be used by an application to display important information about a program The splash screen can also be used as an activity indicator during application startup A splash screen is usually used when it is known that an application will take more than a sec ond or two to display its first UI elements The splash screen gives the user visual feedback that the application is starting If a splash screen is not used the user may assume that the start command was not run properly and the user may try to start the application again FAQ 361 To display a splash window create an overlapped window In the WndProc for this window intercept the WM_NCCALCSIZE message and return NULL instead of the DefWindowProc function which prevents Microsoft Windows from redefining the window s maximum default full screen client area size to accommodate borders and caption bar This window can be created before the main application initializes The main application can send messages to this window to display its initialization information
29. timeptr gt tm_mday timeptr gt tm_hour timeptr gt tm_min timeptr gt tm_sec 1900 timeptr gt tm_year return result This function is supposed to output a character string of 26 positions at most including the ter minating zero If we count the length indicated by the format directives we arrive at 25 o 3 for the day of the week o l space o 3 for the month o 3 for the day in the month o space o 8 for the hour in hh mm ss format o space o 4 for the year o newline It makes 25 characters and taking into account the terminating zero the calculation seems OK But it is not The problem is that the format d of the printf specification doesn t allow for a maximum size When you write 3d it means that at least 3 characters will be output but it could be much more if for instance the input is bigger than 999 Buffer overflows 139 In that case the buffer allocated for asctime is too small to contain the printf result and a buf fer overflow will happen The consequences of that overflow will change from system to sys tem depending on what data is stored beyond that buffer the alignment used for character strings etc If for instance a function pointer is stored just beyond the buffer the conse quences could be catastrophic in the sense that it would be very difficult to trace where the error is happening 1 28 1 1 Getting rid of buffer overflows How much buffer space we
30. to the linker IccInk that builds the executable Organizing all those steps and typing all those command lines can be boring To make this eas ier the IDE will do all of this with the F9 function key 1 3 5 The run time environment The program starts in your machine A specific operating system is running a certain file and hard disk configuration is present you have so many RAM chips installed etc This is the run time environment The file built by the linker Icclnk is started through a user action you double click in its icon or by giving its name at a command shell prompt or by the action of another program that requests to the operating system to start it The operating system accesses the hard disk at the specified location and reads all the data in the file into RAM Then it determines where the program starts and sets the program counter of the printed circuit in your computer to that memory location The piece of code that starts is the startup stub a small program that does some initialization and calls the main procedure It pushes the arguments to main in the same way as for any other procedure 8 C programming with Icc win32 The main function starts by calling another function in the C library called printf This func tion writes characters using a console emulation where the window is just text This envi ronment is simpler conceptually and it is better suited to many things for peopl
31. 1 2 Programming with security in mind The C language doesn t give you many security nets Actually there is no security net You are supposed to make no mistakes This is very difficult to achieve of course Here I will try to give you some simple advice that you can use in your code to make it safer and more robust 1 2 1 Always include a default in every switch statement It is very common that you write a switch statement just taking into account the normal cases i e the ones you expect This is not very clever if the data doesn t fit into the expected cases since the program will go on after the switch statement even with a completely unex pected result This will lead to strange errors further down what makes the error discovering more difficult Always include a default case even if you just write switch input case XX default assert 0 The assert macro defined in lt assert h gt will stop the program with a clear error message indi cating the source line and file of the faulty code This means that you will be informed when an unexpected data item arrives and you can correct this during the debug phase 1 2 2 Pay attention to strlen and strcpy As we have seen before See page 89 the strlen and strcpy functions expect a well formed C string The st rlen function will not stop until a zero byte is found This is not very dangerous since strlen just reads memory without modifying it Our st
32. Easy isn t it We declare our word table now like this WORDLIST WordTable Oxffff 1 1 31 2 Memory organization Now we write the constructor for our word list structure It should get more memory from the system to hold the new structure and initialize its fields WORDLIST NewWordList char word int len strlen word WORDLIST result more_memory sizeof WORDLIST len 1 result gt Count 1 strcpy result gt Word word return result We allocate more memory to hold the structure the characters in the word and the terminating zero Then we copy the characters from the buffer we got set the count to 1 since we have seen this word at least once and return the result Note that we do not test for failure We rely on more_memory to stop the program if there isn t any more memory left since the pro gram can t go on if we have exhausted the machine resources Under windows the implementation of the standard malloc function is very slow To avoid calling malloc too often we devise an intermediate structure that will hold chunks of mem ory calling malloc only when each chunk is exhausted typedef struct memory int used int size char memory MEMORY Now we write our memory allocator define MEM ALLOC SIZE Oxffff int memoryused 0 void more_memory int siz static MEMORY mem void result if mem NULL mem gt used siz gt mem gt size mem m
33. HWND Start GetDesktopWindow HWND hTree GetDlgItem parent IDTREEWINDOW TV_INSERTSTRUCT TreeCtrlitem HTREEITEM hNewNode memset amp TreeCtrliItem 0 sizeof TreeCtrlItem TreeCtrlitem hParent TVI_ROOT TreeCtrlitem hiIinsertAfter TVI_LAST TreeCtrliItem item mask TVIF_TEXT TVIF_PARAM TreeCtrlItem item pszText Desktop hNewNode TreeView_InsertItem hTree amp TreeCtrliItem Start GetWindow Start GW_CHILD Scan hTree hNewNode Start return 1 We start at the start and we ask windows to give us the window handle of the desktop window We will need the tree window handle too so we use GetDlgItem with the parent window of the tree control and it s ID This works even if the parent window is a normal window and not a dialog window We go on by filling our TV_INSERTSTRUCT with the right values This is a common inter face for many window functions Instead of passing n parameters we just fill a structure and pass a pointer to it to the system Of course it is always a good idea to clean the memory space with zeroes before using it so we zero it with the memset function Then we fill the fields we need We say that this item is the root item that the insertion should happen after the last item that the item will contain the text Desktop and that we want to reserve place for a pointer in the item itself TVIF_PARA
34. Icc win like many other C compilers adds always an underscore to the names it generates for the linker gt Since our function is declared as _stdcall windows conventions require that we add to the name of the function the character followed by the size of the function arguments Since our function takes a char pointer size 4 another char pointer and an integer size 4 too we have 12 bytes of procedure arguments hence the 12 Note that all types smaller than an integer will be automatically be promoted to integers when passing them to a function to keep the stack always aligned so that we shouldn t just take the size of the arguments to make the addi tion All of this can become really complicated if we have structures that are pushed by value into the stack or other goodies The best thing would be that our DLL would export _GetString 12 as GetString PERIOD Well this is exactly where our dialog def file comes handy Here is a dialog def that will solve our problem LIBRARY dialog EXPORTS _GetString 12 GetString We have in the first line just the name of the DLL in a LIBRARY statement and in the second line two names The first one is the name as exported by the compiler and the second one is the name as it should be visible from outside By default both are the same but now we can separate them With these instructions the linker will put in the export table of the DLL the 116 character string GetS
35. J We test immediately if the correct number of arguments has been given If not we exit with a clear error message I if argc lt 3 fprintf stderr Usage paste filel file2 n exit EXIT_FAILURE We open both files taking care not to open the same file twice We test with strcmp if they are equal sy f1 fopen argv 1 r if strcmp argv 1 argv 2 2 fopen argv 2 r else 2 f1 la We read line after line of the first file until we reach the end of the first file ai while fgets buf1 MAXLINELEN f1 char p strchr bufl1 n la the fgets function leaves a n in the input We erase it if it is there We use for this the strchr function that returns the first occurrence of a character in a string and returns a pointer to it If it doesn t it returns NULL so we test below before using that pointer st if p p 0 We output the first file line separated from the next with a single tabulation char printf s t buf1 If there are still lines to be read from file 2 we read them and we print them after doing the same treatment as above ay if f2 1 amp amp fgets buf2 MAXLINELEN 2 p strchr buf2 n if p p 0 printf s n buf2 la If we are duplicating the same file just print the same line again Simple programs 95 T else printf s n buf1 End of the while loop When we arrive here the first file has been comp
36. Note again that in C array indexes start at zero The fourth element is numbered 3 Many other structures are possible their number is infinite struct customer int ID char Name char Address double balance time_t lastTransaction unsigned hasACar 1 unsigned mailedAlready 1 112 C programming with Icc win32 This is a consecutive amount of storage where e an integer contains the ID of the customer e a machine address pointing to the start of the character string with the customer name e another address pointing to the start of the name of the place where this customer lives e a double precision number containing the current balance e atime_t time type date of last transaction e and other bit fields for storing some flags struct mailMessage MessageID ID time_t date char Sender char Subject char Text char Attachements This one starts with another type containing the message ID again a time_t to store the date then the addresses of some character strings The set of functions that use a certain type are the methods that you use for that type maybe in combination with other types There is no implicit this in C Each argument to a function is explicit and there is no predominance of anyone A customer can send amailMessage to the company and certain functions are possible that handle mailMessages from customers Other mailMessages aren t from custom ers and are handled differently
37. Since our library should be independent whether it is called from a windows program or a console application we should test that now Additional files to be included in the link dialog lib teconio lib Now when creating the project we ask the wizard to create a console application We leave everything by default but when we arrive at the linker settings dialog we add our dialog lib to the libraries entry field like this Another issue to remember is the following We need a resource file Since in our library there are no resources we have to add those resources to our test program This is easy to do in this case we just add the dialog rc resource file to the project The interface for the users of the library however is terrible All programs that use our library will be forced to include somehow the resource for the dialog box Includ ing a resource in another resource file is difficult to say the least Wow this looks like a showstopper actually OK This presents an unexpected and serious trouble for our library project but we will not leave things at midway We finish our test program by changing our main function like this extern int APIENTRY GetString char prompt char buf int len int main void char buffer 1024 if GetString Enter a string buffer sizeof buffer printf String is s n buffer else printf User cancelled n return 0 113 It could be argued that thi
38. Some people like to store data in their windows We tell windows that it should reserve some space in this case the DLGWINDOWEXTRA constant that in win h is defined as 30 We put in this structure too for obscure historical reasons the hinst handle that we received in WinMain We tell the system that the cursor that this window uses is the system cursor i e an arrow We do this with the API LoadCursor that returns a handle for the cursor we want The brush that will be used to paint this window will be white and the class name is the character string dialog And finally we just call the RegisterClass API with a pointer to our structure Windows does its thing and returns The last statement of WinMain is worth some explanation Now we have a registered class and we call the DialogBox API with the following parameters DialogBox hinst MAKEINTRESOURCE IDD_MAINDIALOG NULL DLGPROC DialogFunc The hinst parameter that many APIs still want is the one we received from the system as a parameter to WinMain Then we use the MAKEINTRESOURCE macro to trick the compiler into making a special pointer from a small integer IDD_MAINDIALOG that in the header file generated by the wizard is defined as 100 That header file is called dialogres h and is quite small We will come to it later What is this MAKE INTRESOURCE macro Again history history In the prototype of the DialogBox API the
39. When the function definition finishes the file scope is again the current scope and Counter reverts to its value of 780 The linkage of an identifier refers to the visibility to other modules Basically all identifiers that appear at a global scope file scope and refer to some object are visible from other mod ules unless you explicitly declare otherwise by using the static keyword Problems can appear if you first declare an identifier as static and later on you define it as external For instance static void foo void and several hundred lines below you declare void foo void Which one should the compiler use static or not static That is the question Lcc win chooses always non static to the contrary of Microsoft s compiler that chooses always static Note that the behavior of the compiler is explicitly left undefined in the stan dard so both behaviors are correct 1 23 Top down analysis The goal of this introduction is not to show you a lot of code but to tell you how that code is constructed A central point in software construction is learning how you decompose a task in sub tasks so that the whole is more modular and easier to manage and change Let s go back to our frequencies example We see that the main function accomplishes several tasks it checks its arguments opens a file checks the result initializes the Frequency array etc This is an example of a monolithic hi
40. Xy X ger type that an implementation offers In the case of lcc win thisis long long q f g e Means the argument is of type qf loat 350 bits precision This is an extension of Icc win t Cy Bp Gr Ua Means the argument is pt rdiff_t under Icc win int Zz dp ip Oy Means the argument is size_t in lcc win unsigned int with Well now we can pass to the final part 78 C programming with Icc win32 1 14 4 The conversions Signed integer conversion is used and the argument is by default of type int If the h modifier is present the argument should be a short if the 11 modifier is present the argument isa Long long Unsigned decimal conversion Argument should be of type unsigned int default unsigned short h modifier or unsigned long long 1 modifier po Unsigned octal conversion is done Same argument as the u format Unsigned hexadecimal conversion If x is used the letters will be in lower case if X is used they will be in uppercase If the modifier is present the number will be prefixed with 0x The argument is printed as a character or a wide character if the 1 modifier is present The argument is printed as a string and should be a pointer to byte sized charac ters default or wide characters if the modifier is present If no precision is given all characters are used until the zero byte is found Otherwise the maxi mum number of characters u
41. box will refuse to close even if we press the OK button We force the user to enter some text before closing the dialog Since we haven t changed anything in the logic for the Cancel but ton the dialog box will still close when the user presses those buttons Only the behavior of the OK button will change The EndDialog API takes two parameters the dialog box window handle that it should destroy and a second integer parameter The dialog box will return these values as the result of the DialogBox call from WinMain remember Since WinMain returns itself this value as its result the value returned by the DialogBox will be the return value of the program 2 1 4 Amore advanced dialog box procedure Doing nothing and not closing the dialog box when the user presses OK is not a good inter face You expect a dialog box to go away when you press OK don t you A user interface like this makes for an unexpected behavior Besides if we put ourselves in the user s shoes how can he she find out what is wrong The software doesn t explain anything doesn t tell the user what to do to correct the situation it just silently ignores the input This is the worst behavior we could imagine Well there are two solutions for this We can disable the OK button so that this problem doesn t appear at all or we could put up a message using our MessageBox API informing the user that a text must be entered Let s see how we would implement the
42. clientService sin_addr s_addr inet_addr 127 0 0 1 clientService sin_port htons 49025 Call the connect function passing the created socket and the sockaddr_in structure as parame ters int rc re connect Socket SOCKADDR amp clientService sizeof clientService if rc SOCKET_ERROR printf Failed to connect n 3 7 4 Sending and receiving data We can receive data from the network using the recv function A typical call looks like this int bytesReceived recv Socket buffer sizeof buffer 0 If we want to receive text we ensure the zero terminated string with buffer sizeof buffer 1 0 bytesReceived recv Socket buffer sizeof buffer 1 0 To send data we use the send function bytesSent send Socket buffer strlen buffer 0 This sends a character string through the network without the trailing zero 3 7 5 Simplifying sockets programming with Icc win Lcc win provides functions that relieve you from programming all the above A client looks like this include lt stdio h gt include lt stdlib h gt include netutils h int main int argc char argv Session session char buf 256 Client Server programming using sockets 403 memset amp session 0 sizeof session session port 25876 session Host 127 0 0 1 if ClientConnect amp session printf Unable to connect n goto end if Send amp session
43. code to copy the image DC onto the destination DC Use BitBlt to copy the contents of the destination DC to the appropriate portion of the screen The following code is a function that demonstrates the preceding steps void DrawTransparentBitmap HDC hdc HBITMAP short yStart hBitmap short xStart COLORREF cTransparentColor BITMAP bm COLORREF cColor HBITMAP bmAndBack bmAndObject bmAndMem bmSave HBITMAP bmBackOld bmObjectOld bmMemOld bmSaveOld HDC hdcMem hdcBack hdcObject hdcTemp hdcSave POINT ptSize hdcTemp CreateCompatibleDC hdc SelectObject hdcTemp hBitmap Select the bitmap GetObject hBitmap sizeof BITMAP ptSize x bm bmWidth ptSize y bm bmHeight DPtoLP hdcTemp amp ptSize LPSTR amp bm Get width of bitmap Get height of bitmap 1 Convert from device to logical points Create some DCs to hold temporary data hdcBack CreateCompatibleDC hdc hdcObject CreateCompatibleDC hdc hdcMem CreateCompatibleDC hdc hdcSave CreateCompatibleDC hdc Create a bitmap for each DC DCs are required for a number of GDI functions Monochrome DC bmAndBack CreateBitmap ptSize x ptSize y 1 1 NULL Monochrome DC 356 C Tutorial bmAndObject CreateBitmap ptSize x ptSize y 1 1 NULL bmAndMem CreateCompatibleBitmap hdc ptSize x ptSize y bmSave CreateCompatibleBitmap hdc ptSize x ptSize y
44. color return hBrush case WM_NCDESTROY DeleteObject hBrush break We create the brush at the initialization of the list box we use it when we receive the WM_CTLCOLORLISTBOX message WM_NCDESTROY message and we destroy it when we receive the This technique can be used not only with list boxes but with many other controls We have Message Control WM_CTLCOLORBTN Button WM_CTLCOLOREDIT Edit field WM_CTLCOLORDLG Dialog box WM_CTLCOLORLISTBOX List box WM_CTLCOLORSCROLLBAR Scroll bar WM_CTLCOLORSTATIC Static controls text etc WM_CTLCOLORLISTBOX WM_CTLCOLOREDIT A combo box sends both messages to the parent window All this messages have the same parameters as exactly the same in the list box example and the procedure is The WM_CTLCOLORSTATIC is interesting because it allows you to add text in any font and color combination to a window or dialog by just calling SelectObject with a special font or font size using the passed HDC of this message 302 C Tutorial 2 14 2 Using the WM_DRAWITEM message Suppose we want to draw a list box that draws an image at the left side of the text in each line In this case just setting some properties of the HDC we receive with WM_CTLCOLORLISTBOX will not cut it We need to do the entire drawing of each line of the list box We can do this by setting the style of the list box to owner draw the resource editor will
45. depending on the concrete application Because that s the point here an application is a coherent set of types that performs a certain task with the computer for instance sending automated mailings or invoices or sensing the temperature of the system and acting accordingly in a multi processing robot or whatever It is up to you actually Note that in C there is no provision or compiler support for associating methods in the struc ture definitions You can of course make structures like this struct customer int ID char Name char Address double balance time_t lastTransaction unsigned hasACar 1 unsigned mailedAlready 1 bool UpdateBalance struct customer Customer double newBalance The new field is a function pointer that contains the address of a function that returns a Bool ean result and takes a customer and a new balance and should eventually update the balance field that isn t directly accessed by the software other than trough this procedure pointer When the program starts you assign to each structure in the creation procedure for it the func tion DefaultGetBalance that takes the right arguments and does hopefully the right thing Structures and unions 113 This allows you the flexibility of assigning different functions to a customer for calculating his her balance according to data that is known only at runtime Customers with a long history of overdraws could be handled diffe
46. dialog name and look at this lines IDD_MAINDIALOG DIALOG 7 20 195 86 1 STYLE DS_MODALFRAME WS_POPUP WS_VISIBLE WS_CAPTION WS_SYSMENU 2 CAPTION dialog 3 FONT 8 Helv 4 BEGIN DEFPUSHBUTTON OK IDOK 149 6 40 14 5 PUSHBUTTON Cancel IDCANCEL 149 23 40 14 6 END We see that all those statements concern the dialog box its appearance the position of its child windows etc Let s go statement by statement 1 We find here the same identifier IDD_MAINDIALOG and then the DIALOG statement together with some coordinates Those coordinates are expressed in Dialog Units not in pixels The motivation behind this is to make dialog boxes that will look similar at all resolutions and with different screen sizes The units are based somehow in the size of the system font and there are APIs to get from those units into pixels and from pixels into those units 104 You will be prompted for a header file where are stored the definitions for things like IDD_MAINDIALOG Choose the one generated by the wizard Its name is lt project name gt res h i e for a project named test we would have testres h 234 C Tutorial 2 The STYLE statement tells the interpreter which things should be done when creating the window We will see later when we create a real window and not a dialog box window that there can be quite a lot of them In
47. hDC 3 0 20000 2500 0 4000 0 18 1 EndPaint hwnd amp ps We call the windows API BeginPaint passing it the address of a PAINTSTRUCT a struc ture filled by that function that contains more information about the region that is to be painted etc We do not use it the information in it because for simplicity we will repaint the Numerical calculations in C 285 whole window each time we receive the message even if we could do better and just repaint the rectangle that windows passes to us in that parameter Then we call the code to draw our galaxy and inform windows that we are done with painting Well this finishes the coding We need to add the include lt math h gt include lt time h gt at the beginning of the file since we use functions of the math library and the time function to seed the srand function We compile and we obtain fal winexample ofl x File Edit Help It would look better if we make a better background and draw more realistic arms but for a start this is enough 286 C Tutorial There are many functions for drawing under windows of course Here is a table that provides short descriptions of the most useful ones Function Purpose AngleArc Draws a line segment and an arc ee Draws an elliptical arc using the currently selected pen You specify the bounding rectangle for the arc ArcTo is similar to the Arc function except that the ArcTo current posit
48. hashfn char HASH TABLE result GC_malloc sizeof HASH TABLE result gt hashfn hashfn return result To add an element we write LIST HashTableInsert HASH TABLE table char str int h table gt hashfn str LIST slotp table gt Table h HASHELEMENTS while slotp if strcmp str char slotp gt data return slotp slotp slotp gt Next Using structures continued 167 return Append amp table gt Table h HASHELEMENTS element All those casts are necessary because we use our generic list implementation with a void pointer If we would modify our list definition to use a char instead they wouldn t be neces sary We first call the hash function that returns an integer We use that integer to index the table in our hash table structure getting the head of a list of strings that have the same hash code We go through the list to ensure that there isn t already a string with the same contents If we find the string we return it If we do not find it we append to that list our string The great advantage of hash tables over lists is that if our hash function is a good one 1 e one that returns a smooth spread for the string values we will in average need only n 128 compar isons n being the number of elements in the table This is an improvement over two orders of magnitude over normal lists 168 C programming with Icc win32 1 34 A closer look at the
49. integer variable and we test if the result is one i e the user pressed OK If that is the case we copy the string from the temporary buffer to the destination buffer Note that we use the strncpy function This standard library function takes an extra parameter a maximum length to copy We do not want to overflow the destination buffer under any circumstances so we only copy a maximum of bufferlen characters minus one to account for the terminating zero of the string We ensure afterwards that the string is zero terminated and we return the result The rest of the program remains the same so it is not shown It is important to remember to get rid of that MessageBox call however Ne We compile the library and we want to test it but we need a test program A library is not an executable by itself Besides this we need a header file that the user of the library will use to get the prototype of our function Its contents are very simple int GetString char prompt char destBuffer int bufferlen and that s all 112 Well this is not great deal we have just to answer YES when it proposes to create the skeleton Libraries 249 Now we have to define a new project that will contain the test code We do that in the same way as we have created the other projects we choose the Create project option in the Proj ect menu bar and we name it appropriately testdialog We do NOT specify a windows application
50. p NULL _try p A printf s n p _ except EXCEPTION_EXECUTE_HANDLER p abc __ retry return 0 The first execution of the __try yields an exception since the pointer p is NULL Within the except block we correct this condition by assigning to that pointer a valid value then we restart with the __retry The output of this program is Abc 1 36 6 The signal function Besides the structured exception handling mechanism outlined above Icc win offers the stan dard signal utility of the standard C language 1 36 6 1 Software signals Software signals are the same thing as the exceptions we described in the proceeding para graphs They can be raised by the CPU traps or simply raised by the function raise To give you an idea of how this mechanism works let s repeat the example of above structured exception handling using the signal mechanism include lt signal h gt include lt stdio h gt include lt stdlib h gt For exit Advanced C programming with Icc win 189 This function will be called by the signal mechanism when a SIGSEGV is raised void traphandler int s printf Illegal address exception n exit EXIT_FAILURE int main void char p NULL Set the function to handle SIGSEGV signal SIGSEGV traphandler p 0 return 0 This will produce the following output D lcc test gt tsignal Illegal address exception To make it easy to
51. result gt FindData amp fd sizeof struct _finddata_t Well we are passing it a structure and the poor function is expecting a pointer This is a serious error We correct it like this memcpy amp result gt FindData amp fd sizeof struct _finddata_t We take the address of the destination structure using the address of operator amp We see that we would have never known of this error until run time when our program would have crashed with no apparent reason a difficult error to find Note always use the right header file to avoid this kind of errors Our program now looks like this include lt stdio h gt We need it for using the FILE structure include lt stdlib h gt We need it for using malloc 128 C programming with Icc win32 include lt io h gt We need it for using findfirst findnext include lt string h gt We need it for memcpy typedef struct tagChars int CharacterValue The ASCII value of the character int Frequency How many seen so far CHARS typedef struct tagStream char Name Input name with possible or chars in it struct _finddata_t FindData long handle FILE file An open file STREAM CHARS Frequencies 256 Array of frequencies int compare Skipped it is the same as above STREAM checkargs int argc char argv STREAM infile NULL long findfirstResult struct _finddata_t fd if arge lt 2 Test if enough arguments
52. t t t s ctime amp ltime Display UTC See note 1 in text gmt gmtime amp ltime 93 ltime printf Coordinated universal time t t s asctime gmt Convert to time structure and adjust for PM if necessary today localtime amp ltime if today gt tm_hour gt 12 strcpy ampm PM today gt tm_hour 12 160 C programming with Icc win32 if today gt tm_hour 0 Adjust if midnight hour today gt tm_hour 12 See note 2 in text printf 12 hour time t t t t 8s s n asctime today 11 ampm Print additional time information ftime amp tstruct printf Plus milliseconds t t t u n tstruct millitm printf Zone difference in seconds from UTC t u n tstruct timezone printf Time zone name t t t t s n _tzname 0 printf Daylight savings t t t s n See note 3 in text tstruct dstflag YES NO Make time for noon on Christmas 1993 if mktime amp xmas time_t 1 printf Christmas t t t t s n asctime amp xmas Use time structure to build a customized time string today localtime amp ltime Use strftime to build a customized time string strftime tmpbuf 128 Today is A day d of the month of B in the year Y n today printf tmpbuf We use this opportunity for introducing new C constructs We see the function call
53. 0 In the above case the code for failure 0 will not be less than zero and it will not be detected as a failure code Rule Do not use the FAILED or SUCCEEDED macros for anything other than HRESULTS Since you know that FALSE is defined as zero FAILED FALSE is zero not really an expected result The opposite problem leads to headaches too Always use the FAI ros with HRESULTS and never write things like this HRESULT hr hr ISomething gt DoSomething if hr WRONG return LE D SUCCEEI DE D mac Error handling under windows 333 Note too that in their infinite wisdom the designers of this API decided that S_FALSE is a success code NOT a failure code and it is defined as 1 one This means that SUCCEEDED S_FALSE TRUE Nice isn t it 2 19 1 Check the return status of any API call Consider this code TCHAR cDriveLetter TCHAR szWindowsDir MAX_PATH GetWindowsDirectory szWindowsDir MAX_PATH cDriveLetter szWindowsDir 0 WRONG If the call to GetWindowsDirectory fails the program will access uninitialized memory This means that the drive value will be a random number between 0 and 255 Of course it is quite difficult to imagine that GetWindowsDirectory fails or is it In windows using Terminal Server it becomes much more complicated to figure out where is the windows directory of a parti
54. 0 printf 3c 4d d n Frequencies count CharacterValue Frequencies count CharacterValue Frequencies count Frequency return 0 We transformed our integer array Frequencies into a CHARS array with very few changes just the declaration Note that the array is still accessed as a normal array would By the way it is a normal array We changed our compare function too obviously since we are now comparing two CHARS structures and not just two integers We have to cast our arguments into pointers to CHARS and I decided that using two temporary variables would be clearer than a complicated expres sion that would eliminate those The initialization of the CharacterValue field is trivially done in a loop just before we start counting chars We assign to each character an integer from 0 to 256 that s all When we print our results we use that field to get to the name of the character since our array that before qsort was neatly ordered by characters is now ordered by frequency As before we write the character as a letter with the c directive and as a number with the d directive When we call this program with frequencies frequencies c we obtain at last 1311 chars in file 32 154 e 101 77 n 110 60 105 59 r 114 59 G 99 32 116 46 wu dT 35 a 97 34 A E S9 29 o 11I 29 f 102 27 Using structures 119
55. 0 flag 47 Why is this field named width I do not really know but it is a misnomer that can lead to error The printf family 77 1 14 2 2 The precision In floating point numbers formats g G f e E this indicates the number of digits to be printed after the decimal point Used with the s format strings it indicates the maximum number of characters that should be used from the input string If the precision is zero the floating point number will not be followed by a period and rounded to the nearest integer 1 14 3 The size specification This table shows the different size specifications together with the formats they can be used 1 d i o u x X The letter 1 with this formats means long or unsigned long 1 n The letter 1 with the n format means long c Used with the c character format it means the character string is in wide character format all others No effect is ignored d i o u x X The letters Ll mean long longorunsigned long long n With this format 11 means long long d 1i 0 u x X With this formats h indicates short orunsigned short Means short Oy 1 pO Up XX Means char or unsigned char n Means char orunsigned char ol 5 A a E e Means that the argument isa long double Notice that the 1 By Ep GyGy modifier has no effect with those formats It is uppercase L j ds iy Oy uy Means the argument is of type intmax_t Le the biggest inte
56. 239 give to the SetFocus function the result of calling the API GetDlgItem This is nice since we actually need only one window handle the window handle of the dialog box that windows gives to us to get all other window handles of interest Now comes a more difficult problem When the user presses the OK button we want to get the text that he she entered How do we do that We have two problems in one the first is to decide when we want to get the text and the other is how to get that text For the first one the answer is clear We want to read the text only when the user presses the OK button If the Cancel button is pressed or the window is closed we surely aren t interested in the text if any We will read the text then when we handle the message that the OK button window sends to us when is pressed We change our dialog procedure like this case WM_COMMAND switch LOWORD wParam case IDOK ReadText hwndDlg EndDialog hwndDlg 1 return 1 case IDCANCEL EndDialog hwndDlg 0 return 1 break We add a call to a function that will get the text into a buffer That function looks like this static char buffer 1024 int ReadText HWND hwnd memset buffer 0 sizeof buffer if GetDlgItemText hwnd IDENTRYFIELD buffer sizeof buffer return 1 return 0 We define a buffer that will not be visible from other modules hence static We set a fixed buf
57. 37 1 2 Double 64 bit format This format uses one bit for the sign 11 bits for the exponent and 52 bits for the fraction struct doubleFormat unsigned FractionLow unsigned FractionHigh 22 unsigned sign 1 194 C programming with Icc win32 Bits 0 51 contain the 52 bit fraction f with bit 0 the least significant and bit 51 the most sig nificant bits 52 62 contain the 11 bit biased exponent e and bit 63 contains the sign bit s The normalized numbers are represented with 1 s x 251023 x 1 f The bias for the exponent in this case is 1023 The range of this format is from 7fefffff ffffffff to 00100000 00000000 in decimal from 1 7976931348623157e 308 to 2 2250738585072014e 308 This numbers are defined in float h as DBL_MAX and DBL_MIN respectively The number of significant digits is 15 defined as DBL_DIG 1 37 1 3 Long double 80 bit format This format uses one bit for the sign 15 bits for the biased exponent and 64 bits for the frac tion Bits 0 63 contain the fraction the bits 64 78 store the exponent and bit 79 contains the sign struct longdoubleFormat unsigned FractionLow unsigned FractionHigh unsigned Exponent 15 unsigned sign 1 The bias for the exponent is 16383 and the formula is 1 s x 2 16383 x 1 f The range of this format is from 7ffe ffffffff ffffffff to 0001 80000000 00000000 or in decimal notation from 1 18973149535723176505e 4932 to 3 36210314311209350626e 4932 Quite en
58. 37 2 2 Precision What is the precision of those numbers We modify the first program as follows int main void float f 1 0f fctf 1 0 fctf fact 34 0 f fctf 1 0 Add one to fctf if fctf f l fctf is equal to fctf printf OK n else printf Not ok n return 0 We obtain the factorial of 34 We add to it 1 Then we compare if it is equal or not to the same number Against all mathematical expectations our program prints Not ok In floating point maths 1 N N Why this The density of our format makes the gaps between one number and the next one bigger and bigger as the magnitude of the numbers increases At the extreme of the scale almost at over flow the density of our numbers is extremely thin We can get an idea of the size of the gaps by writing this int main void float f 1 0f fctf 1 0 fctf fact 34 0 f 1 0 while fctf f fctf f 10 0f 198 C programming with Icc win32 printf Needs e n return 0 We get the output Needs 1 000000e 019 We see that the gap between the numbers is huge 1e19 What are the results for double precision We modify our program and we get Needs 1 000000e 019 What Why are the results of double precision identical to the floating point precision We should find that the smallest format would yield gaps much wider than the other more precise format Looking at th
59. 4 bits Pe union dd union id Reserve storage for the biggest of the declared doubler d declarations types and store all of them in the same place EREE i 73 s int id 2 I see Union on page 58 y enum identifier Define an enumeration of comma separated enum color enum list identifiers assigning them some integer value red green blu see Enum on page 59 const type identifier Declare that the given identifier can t be changed assigned to within this scope see Const on page 60 const int a unsigned int type When applied to integer types do not use the sign bit see Unsigned on page 62 unsigned char a 178 volatile type identifier Declare that the given object changes in ways unknown to the implementation The compiler will not store this variable in a register even if optimizations are turned on volatile int hardware_clock 44 C programming with Icc win32 type id args Declare the prototype for the given function The arguments are a comma separated list see Prototypes on page 59 double sqrt double x type id args Declare a function pointer called id with the given return type and arguments list void fn int id Declare a label labl type fn args statements Definition of a function with return type lt type gt int addl int x interfaces for m
60. 89 strchr 89 strlen 89 isoowerOfTwo 90 Write isoowerOfTwo without any loops 91 striwr 92 paste 93 Using arrays and sorting 97 How to sort arrays 100 Other qsort applications 105 Summary of Arrays and sorting 107 Pointers and references 107 Structures and unions 110 Structures 110 Structure size 113 Defining new types 114 Unions 115 Using structures 117 Fine points of structure use 119 I dentifier scope and linkage 120 Top down analysis 121 Extending a program 124 Improving the design 129 Traditional string representation in C 130 The problems with C Strings 132 Buffer overflows 135 A buffer overflow in the C standard document 138 Memory management and memory layout 141 Functions for memory allocation 143 Memory layout under windows 143 Memory management strategies 145 Static buffers 145 Stack based allocation 145 Arena based allocation 146 The malloc free strategy 146 The malloc with no free strategy 147 Automatic freeing garbage collection 147 Mixed strategies 148 A debugging implementation of malloc 148 Counting words 152 The organization of the table 153 Memory organization 155 Displaying the results 156 Code review 158 Time and Date functions 158 Using structures continued 163 Lists 163 Hash tables 166 A closer look at the pre processor 168 Preprocessor commands 169 Things to watch when using the preprocessor 172 Using function pointers 174 Advanced C programming with Icc win 179 O
61. AT amp T not Intel as is with most other compilers 2 24 Overview of Icc win s documentation The documentation of Icc win comes in four files Bibliography 385 6 Manual chm This is the user s manual where you will find information about how the system is used command line options menu descriptions how to use the debugger etc It explains how to build a project how to setup the compiler each compiler option all that with all the details 7 c library chm This file contains the documentation for all functions in the C runtime library It will be automatically invoked by the IDE when you press the F1 function key This two files c library chm and manual chm are distributed in manual exe 8 Lee win doc This is a technical description for interested users that may want to know how the system is built how the programs that build it were designed the options I had when writing them etc The documentation of the windows API is distributed in a relatively large file called win32hlp exe This is absolutely essential unless you know it by heart When installed this file will become Win32 hlp That file is not complete however More documentation for the new features of Win32 can be found in the win32apidoc exe file also in the Icc distribution site When installed that file will install e Shelldoc doc This documents the windows shell its interfaces function definitions etc e Wininet doc This documents the T
62. Both cases unless treated by the program will produce incorrect results Historically integer overflow has never been treated by the language with the attention it deserves Everything is done to make programs run fast but much less is done to make pro grams run correctly giving as a result programs that can return wrong results at an amazing speed Icc win is the only C compiler that gives the user access to the overflow flag in a similar and efficient way that the programmer has access to the floating point exception flags The built in function A closer view 57 int _overflow void This function will return 1 when the overflow flag is set zero otherwise To use this feature separate your operations in small steps and call this pseudo function when needed Instead of c bta b b 56 write cl bta if _overflow goto ovfl c2 b b if _overflow goto ovfl c cl c2 56 This can become VERY boring so it is better to give a command line argument to the com piler that will generate the appropiate assembly to test each operation The operations mon itored are signed ones unsigned operations wrap around 1 13 9 Postfix These expressions increment or decrement the expression at their left side returning the old value For instance array 234 678 a array 234 In this code fragment the variable a will get assigned 678 and the array element 234 will have a value of 679 after the exp
63. CompilerDlg psp i pszTitle Compiler itt Now that we have filled the property sheet pages we fill the header data First we set it to zero memset amp psh 0 sizeof PROPSHEETHEADER Then we set the size field flags field and the parent window info psh dwSize sizeof PROPSHEETHEADER psh dwFlags PSH_PROPSHEETPAGE PSH_NOAPPLYNOW psh hwndParent hwndOwner Then the hInst Application instance the caption and the number of pages this property sheet has psh hInstance hInst psh pszCaption Configuration psh nPages i Now we link the header data with the array of property sheet pages we filled above psh ppsp LPCPROPSHEETPAGE amp psp Now we go PropertySheet amp psh FAQ 381 2 22 29 How to tell Windows to run a program during startup You can either place a shortcut to your program in the Windows startup folder or add an entry to the registry for your program If you want to use the shortcut technique then look at the question on how to create a shortcut on the desktop See page 329 You can use the same code but instead of saving the shortcut to the desktop directory save it to the startup directory You can find the startup directory by call ing SHGetSpecialFolderLocation and passing it the CSIDL_STARTUP flag If you prefer to use the registry then you need to create a new entry for your program in the
64. Eat the message so you don t quit the FAQ 379 entire application if PeekMessage amp msg NULL WM_QUIT WM_QUIT PM_REMOVE If you timed out then return zero uiResult 0 return uiResult The key to creating a timed message box is exiting the dialog box message loop internal to the message box Since the message loop for a message box is part of USER you cannot modify it without using hooks and other such methods However all message loops exit when they receive a WM_QUIT message Furthermore a nested message loop if it receives a WM_QUIT message must break the loop and then re post the quit message so that the next outer layer can process it Therefore you can get the nested message loop to exit by calling PostQuitMessage The nested message loop will clean up and post a new quit message When the MessageBox returns you peek to see if there is a quit message If so then it means that the message loop was abnormally terminated You also consume the WM_QUIT message instead of re posting it so that the application continues running Essentially you have tricked the nested mes sage loop into thinking that the application is terminating When it returns you eat the quit message effectively canceling the fake quit that you generated 2 22 28 How do build a Property sheet control For an example of a property sheet control see the Configuration item in Wedit s
65. ExceptionRecord gt ExceptionInformation 0 return 0 This will print Error code 0xe0000001 In function fn The keyword __func__ will be substituted by the name of the current function by the compiler We put that name in the first parameter of the table We call then RaiseException with 1 argument and our table The exception handling code will get the exception information and print the first argument The function GetExceptionInformation returns a pointer to a copy of the exception informa tion received by the system by the Icc win runtime The structure EXCEPTION_POINTERS CON tains two pointers the first points to an EXCEPTION_RECORD and the second to a CONTEXT structure containing the machine registers at the time of the exception In the example we use the exception record to get to the parameters array and we print the first one Nowhere in the shown code there is a test to verify that the exception code is the one we are expecting If another exception had happened that has no parameters or a different set of parameters we would have crashed 186 C programming with Icc win32 1 36 5 5 Catching stack overflow The stack space allocated by windows to a program at start is 4K This stack can grow up to a size of IMB If you go beyond this limit you get a stack overflow exception OxCOOOOOFD This exception will be catched by the structured exception handling framework however
66. GetClientRect hwnd LPRECT amp rMyRect ClientToScreen hwnd LPPOINT amp rMyRect left ClientToScreen hwnd LPPOINT amp rMyRect right 2 22 23 When should I use critical sections and when is a mutex better Critical sections and mutexes provide synchronization that is very similar except that critical sections can be used only by the threads of a single process There are two areas to consider when choosing which method to use within a single process Speed The Synchronization overview says the following about critical sections e Critical section objects provide a slightly faster more efficient mechanism for mutual exclusion synchronization e Critical sections use a processor specific test and set instruction to determine mutual exclusion Deadlock The Synchronization overview says the following about mutexes e Ifa thread terminates without releasing its ownership of a mutex object the mutex is considered to be abandoned A waiting thread can acquire ownership of an abandoned mutex but the wait function s return value indicates that the mutex is abandoned e WaitForSingleObject will return WAIT_ ABANDONED for a mutex that has been abandoned However the resource that the mutex is protecting is left in an unknown state e There is no way to tell whether a critical section has been abandoned 2 22 24 Why is my call to CreateFile failing when I use conin or conout If you attempt to open a c
67. GetNext STREAM stream STREAM result struct _finddata_t fd long findnextResult _findnext stream gt handle amp fd if findnextResult lt 0 return NULL result malloc sizeof STREAM memcpy amp result gt FindData amp fd sizeof struct _finddata_t result gt handle stream gt handle result gt file fopen fd name rb result gt Name stream gt Name return result int main int argc char argv int count 0 STREAM infile checkargs argc argv if infile NULL return 1 Initialize do count ProcessStream infile Frequencies fclose infile gt file infile GetNext infile while infile 0 printf d chars in file n count qsort Frequencies 256 sizeof CHARS compare DisplayOutput Frequencies return 0 1 25 Improving the design There are several remarks that can be done about our program The first one is that the mem ory allocator could very well fail when there is no more memory available When the alloca tor fails it returns NULL Since we never test for this possibility our program would crash in low memory conditions What a shame We arrange for this immediately Instead of using the allocator we will write a function that will call the allocator test the result and call the exit routine if there is no more memory left Continuing processing without more memory is impossible anyway void xmalloc unsigned int siz
68. HKEY_LOCAL_MACHINE Software Microsoft Windows CurrentVersion Run registry folder Windows will launch every program that is in this folder when the OS boots Your reg istry entry should be a string value The value of the string should be the full path to the exe cutable you want to run 2 22 30 How do l disable the screen saver In the main loop of your window procedure answer TRUE to the WM_SYSCOMMAND mes sage like this case WM_SYSCOMMAND if wParam SC_SCREENSAVE return TRUE This disables the screen saver 2 22 31 How do I play a sound You have several APIs to choose from PlaySound It will play a sound file name or a resource from the executable You have a flags argument to specify repeating or other characteristics MessageBeep Just a beep not very sophisticated waveOutxxx This are a series of functions to play sounds with much more control and fine tuning possibilities than the two functions above DirectX The Direct X software contains a direct sound API 2 22 32 How do simulate a key stroke to send it to another window You use the keybd_event API Here is a simple code that turns on the NumLock key include lt windows h gt void SetNumLock BOOL bState BYTE keyState 256 GetKeyboardState LPBYTE amp keyState if bState amp amp keyState VK_NUMLOCK amp 1 bState amp amp keyState VK_NUMLOCK amp 1 Simulate a key press
69. Long and int are compatible for the 32 bit version of Icc In the version of Icc linux for 64 bits however long is 64 bits and int is 32 bits they are no longer compatible types In that version long is compatible with the long long type Plauger and Brody give the following definition for when two types are compatible types Both types are the same Both are pointer types with the same type qualifiers that point to compatible types Both are array types whose elements have compatible types If both specify repetition counts the repetition counts are equal Both are function types whose return types are compatible If both specify types for their parameters both declare the same number of parameters including ellipses and the types of corresponding parameters are compatible Otherwise at least one does not specify types for its parameters If the other specifies types for its parameters it specifies only a fixed number of parameters and does not specify parameters of type float or of any integer types that change when promoted Both are structure union or enumeration types that are declared in different translation units with the same member names Structure members are declared in 18 C programming with Icc win32 the same order Structure and union members whose names match are declared with compatible types Enumeration constants whose names match have the same values 1 6 6 Incomplete types An incomplete type is missing
70. ShellExecute Handle open http www cs virginia edu lcc win32 NULL NULL SW_SHOWDEFAULT 2 18 5 Creating a desktop shortcut Here is a small utility and test program to create a shortcut in the desktop It receives three parameters 1 The name of the file that will be executed by the shell In the example is the lcc compiler 2 The name of the shortcut i e the name that will appear under the shortcut in the desktop 3 An optional commentary string include lt windows h gt include lt objidl h gt include lt shlobj h gt 330 C Tutorial 44 43 int CreateShortCut const char file char shortcutname char ne ude lt shobjidl h gt nc ude lt wchar h gt args TShellLink pLink IPersistFile pPersistFile LPMALLOC ShellMalloc LPITEMIDLIST DesktopPidl char DesktopDir MAX_PATH wchar_t WDesktopDir MAX_PATH BSTR bstr We are going to create a pidl and it will need to be freed by the shell allocator Get the shell allocator object using AP SHGetMalloc function Return zero if failure if FAILED SHGetMalloc amp ShellMalloc return 0 use the API to get a pidl for the desktop directory If function fails return zero if FAILED SHGetSpecialFolderLocation NULL CSIDL_DESKTOPDIRECTORY amp DesktopPidl return 0 Now convert the pidl to a character string return if function fails if SHGetPathFromIDList Des
71. This is the dangling pointer problem A pointer that points to an invalid memory location Memory leaks provoke that the RAM space used by the program is always growing eventu ally provoking a crash if the program runs for enough time for this to become significant In short lived programs this can have no consequences and even be declared as a way of mem ory management The lcc compiler for instance always allocates memory without ever both ering to free it relying upon the operating system to free the memory when the program exits Freeing a piece of RAM twice is much more serious than a simple memory leak It can com pletely confuse the malloc system and provoke that the next allocated piece of RAM will be 142 C programming with Icc win32 the same as another random piece of memory a catastrophe in most cases You write to a vari able and without you knowing it you are writing to another variable at the same time destroy ing all data stored there More easy to find since more or less it always provokes a trap the dangling pointer problem can at any moment become the dreaded show stopper bug that crashes the whole program and makes the user of your program loose all the data he she was working with I would be delighted to tell you how to avoid those bugs but after more than 10 years working with the C language I must confess to you that memory management bugs still plague my pro grams as they plague all other C progra
72. Tst Text label ed Edit field Group box ok Push button a Check box Radio button Z Combo box List box B Horizontal scroll 4 vertical scroll L Rectangle Bl Filled rectangle 2 Icon Month Calendar Ci Tab control it Tree control m Progress control Spin button ef Slider fH DateTime The whole operation of the editor is quite simple The smaller window represents all the controls that you can put in a dialog box entry fields buttons checkboxes and several others You select one button with the mouse and drag it to your dialog box There you drop it at the right position To add an entry field then we just push the edit field icon the third one from the left in the upper row of icons and drag it to our dialog box in the main wedit window After doing this it will look like this m Dialog Title Our entry field becomes the selected item hence the red handles around it After resizing if necessary we need to enter its identi fier i e the symbolic name that we will use in our program to refer to it We will refer then in our program to this entry field with the name IDENTRYFIELD maybe not a very cute name but at least better than some bare number The editor will write a define IDENTRYFIELD 101 in the generated header file The number 101 is an arbitrary constant chosen by the editor We resize the dialog box a bit I like dialogs that aren t bigger than w
73. WH_CLOSE 0 0 break hInstance void Oxl hPrevinstance void 0x1l441e68 lpCmdLine 0x143aa0 20 nCmdShow 4210720 hInst void 0x0 amp auto locals stack events search Stopped DoSearchT ext 208 5 Our program starts running we go to the menu select the search item and Wedit springs into view We hit the breakpoint Well that means at least that we have correctly done things until here the message is being received We enter into the CallDialog procedure using the F8 accelerator We step and after going through the DialogBoxParam procedure we see no dialog and the return result is 1 The debugger display looks like this We see the current line highlighted in yellow and in the lower part we see the values of some variables Some are relevant some are not Luckily the debugger picks up r as the first one Its value is 1 294 C Tutorial Why 1 Wy wedit winexample winexample c fa i Ec j toject Resources Dug Ut M HUND CreatevwinexanpleWndClassWnd void return CreateWindow winexampleWndClass winexample WS_MINIMIZEBOX WS_VISIBLE WS_CLIPSIBLINGS WS_CLIPCHI CW_USEDEFAULT 0 CW_USEDEFAULT 0 NULL NULL hInst NULL int CallDialog int id DLGPROC proc LPARAM parameter int r DialogBoxParfm hIinst MAKEINTRESOURCE id hwndM ide aa static BOOL CALLBACK SearchDlgProc HWND hwnd UINT msg wear _ switch msg case WM_INITDIALOG return TRUE case WM_CLOSE EndD
74. a character string and will fill the fileinfo structure with information about the file it finds if it finds it We can know if findfirst really found something by looking at the return result It will be 1 if there was an error or a unique value otherwise The documentation tell us too that errno the global error variable will be set to ENOENT if there wasn t any file or to EINVAL if the file specification itself contained an error and findfirst couldn t use it Then there is findnext that looks like this int findnext long handle struct _finddata_t fileinfo It uses the unique value returned by findfirst and fills the fileinfo structure if it finds another file that matches the original specification If it doesn t find a file it will return 1 as findfirst If it does find another file it will return zero We see now that a FILE that was uniquely bound to a name is now a possible ambiguous file specification that can contain a _finddata_t whatever that is that can be used to read several FILEs We could formalize this within our program like this typedef struct tagStream char Name struct _finddata_t FindData long handle FILE file STREAM Our function checkargs returns a FILE pointer now It could return a pointer to this STREAM structure we have just defined or NULL if there was an error Our program then Extending a program 125 would loop asking for the next file adding to o
75. a signed short goes from 32768 to 32767 an unsigned short goes from zero to 65535 216 See the standard include file lt 1imits n gt for the ranges of signed and unsigned integer types 1 13 22 Bit fields A bit field is an unsigned or signed integer composed of some number of bits Lcc win will accept some other type than int for a bit field but the real type of a bit field will be always either int or unsigned int For example in the following structure we have 3 bit fields with 1 5 and 7 bits struct S int a 1 int b 5 int c 7 With Icc win the size of this structure will be 4 with no special options With maximum pack ing Zp1 option the size will be two When you need to leave some space between adjacent bit fields you can use the notation unsigned n For example struct S int a 1 int b 5 unsigned 10 int c 7 Between the bit fields a and b we leave 10 unused bits so that c starts at a 16 bit word bound ary 1 13 23 Stdcall Normally the compiler generates assembly code that pushes each argument to the stack exe cutes the call instruction and then adds to the stack the size of the pushed arguments to return the stack pointer to its previous position The stdcall functions however return the stack pointer to its previous position before executing their final return so this stack adjustment is not necessary A closer view 63 The reason for this is a smaller code size since the
76. all this procedures are very similar to each other The other procedure that we need DoSearchText is handled similarly int DoSearchText char txt MessageBox NULL Text to search txt MB_OK return 1 We just show the text to search Not very interesting but 292 C Tutorial We compile link the main application window appears we select the Search menu and we see ZZUyZZuyZZGYZZ ZZ ZZ UYZZGYZZ ZZ OZZUYZZUYZZ GYZZ ZZ UZ Z UYZZ UYZZUYZZ UVZZ UYZZUYZZUYZZ ZZ uyZZuyZZuyZZuy EA a Well we have inverted the parameters to the MessageBox procedure but that s surely not the point Why is the dammed dialog box not showing 130 Well here we need a debugger We need to know what is happening when we call the dia log box We press F5 and we start a debugging session The debugger stops at WinMain C2 wedit winexample winexample c fl case WM_DESTROY PostQuitMessage 0 break default return DefWindowProc hwnd msg wParam lParam OO3 lt G return 0 H x002 lt 00 ee ee E ee int WINAPI WinMain HINSTANCE hInstance HINSTANCE hPrevInst MSG msg HANDLE haAccelTable hInst hInstance if InitApplication return 0 hAccelTable LoaddAccelerators hInst MAKEINTRESOURCE ID if t hwndMain CreatewinexampleWndClassWnd HWND return 0 CreateSBar hwndMain Ready 1 ShowWindow hwndMain SW_SHOW Md hInstance void Oxl hPr
77. an underscore and an upper case letter are reserved by the compiler and should therefore not be used by programmers To be on the safe side it is best to avoid the use of all identifiers beginning with an underscore Microsoft has developed a large set of rules mostly very reasonable ones here http msdn microsoft com library default asp url library en us cpgenref html cpconNamingGuidelines asp 1 13 2 Constants 1 13 2 1 Evaluation of constants The expressions that can appear in the definition of a constant will be evaluated in the same way as the expressions during the execution of the program For instance this will put 1 into the integer constant d static int d 1 This will also put one in the variable d static int d 60 1 1 0 50 C programming with Icc win32 Why The expression 60 1 1 0 is evaluated from left to right It is a boolean expression and its value is 1 if the first expression is different from zero or the value of the second expression if the value of the first one is zero Since 60 is not zero we stop immediately without evaluat ing the second expression what is fortunate since the second one contains an error 1 13 2 2 Integer constants An integer constant begins with a digit but has no period or exponent part It may have a pre fix that specifies its base and a suffix that specifies its type A decimal constant begins with a nonzero digit and consists of a sequence of decimal digits A
78. and using this feature All of them explained in depth in the user s manual This short notice is just a pointer to show you what is possible The implementation of this feature is compatible with the C language that offers a similar facility Many other languages provide this functionality including for instance the venerable FORTRAN language 8 1 36 1 1 How to use this facility Operator overloading is a powerful feature but that doesn t mean that you are exempted from thinking before you write your code Please OK For instance even it is very tempting to do typedef struct _date int year month day hour sec DATE DATE operator DATE d1 DATE d2 DATE operator DATE d1 DATE d2 80 See http www qmw ac uk cgaa260 BUILDING INTR_F90 PRG_UNTS OPOLOAD HTM Opera tor overloading in Fortran90 180 C programming with Icc win32 The operator can t be used for dates There is nothing that can be assigned to 16 July 1970 23 December 1980 The operation has no sense for dates The same applies to multipli cation and division Subtraction is a legal operation for dates but the result type is not a date but a dimensionless number that represents a time interval in days hours etc The only overloaded operator that makes sense then is int operator DATE dl DATE d2 Operator overloading is best done for numbers and similar objects This facility allows you to imple
79. are abstracted under the same concept a FILE as a sequence of bytes to handle The FILE structure is a special opaque structure defined in lt stdio h gt Contrary to other opaque structures its definition is exposed in stdio h but actually its fields are never directly used We have two kinds of input output direct operations and formatted operations In direct oper ations we just enter data from or to the device without any further processing In formatted operations the data is assumed to be of a certain type and it is formatted before being sent to the device As in many other languages to perform some operation with a file you have to setup a connec tion to it by first opening it in some way then you can do input output to it and then even tually you close the connection with the device by closing it Here is a short overview of the functions that use files Name Purpose fopen Opens a file fclose Closes a file fprintf Formatted output to a file fputc Puts a character in a file putchar Puts a character to stdout getchar Reads a character from standard input 33 An opaque structure is a structure whose definition is hidden Normally we have just a pointer to it but nowhere the actual definition 28 C programming with Icc win32 feof Returns true when the current position is at the end of the fi
80. background on the destination DC BitBlt hdcMem 0 0 ptSize x ptSize y hdcTemp 0 0 SRCPAINT Copy the destination to the screen BitBlt hdc xStart yStart ptSize x ptSize y hdcMem 0 0 SRCCOPY Place the original bitmap back into the bitmap sent here BitBlt hdcTemp 0 0 ptSize x ptSize y hdcSave 0 0 SRCCOPY Delete the memory bitmaps DeleteObject SelectObject hdcBack bmBackOld DeleteObject SelectObject hdcObject bmObjectOld DeleteObject SelectObject hdcMem bmMemOld DeleteObject SelectObject hdcSave bmSaveOld Delete the memory DCs DeleteDC hdcMem FAQ 357 DeleteDC hdcBack DeleteDC hdcObject DeleteDC hdcSave DeleteDC hdcTemp The following is an example of how the DrawTransparentBitmap function might be called DrawTransparentBitmap hdc The destination DC hBitmap The bitmap to be drawn xPos X coordinate yPos Y coordinate OxOOFFFFFF The color for transparent pixels white in this example 2 22 5 How do I draw a gradient background DrawBackgroundPattern J Purpose This function draws a gradient pattern that transitions between blue and black This is similar to the background used in Microsoft setup programs void DrawBackgroundPattern HWND hWnd HDC hDC GetDC hWnd Get the DC for the window RECT rectFill Rectangle for
81. be wrong Any pointers that were allocated with malloc will not be released and setjmp longjmp could be the source of a memory leak Within Icc win there is an easy way out since you can use the garbage collector instead of malloc free The garbage collector will detect any unused memory and will released when doing the gc 1 16 2 Register variables and longjmp When you compile with optimizations on the use of setjmp and longjmp can produce quite a few surprises Consider this code include lt set jmp h gt include lt stdio h gt int main void jmp_buf jumper int localVariable 1 1 printf 1 d n localVariable if setjmp jumper 0 return from long jmp localVariable 2 printf 2 d n localVariable long jmp jumper 1 localVariable tt 3 printf 3 Sd n localVariable return 0 Our local Variable starts with the value 1 Then before calling longjmp it is incremented Its value should be two At exit localVariable is incremented again at should be three We would expect the output 1 1 2 2 3 3 And this is indeed the output we get if we compile without any optimizations When we turn optimizations on however we get the output 1 1 2 2 3 2 Why Because localVariable will be stored in a register When longjmp returns it will restore all registers to the values they had when the setjmp was called and if local Variable lives in a reg i
82. calling our DialogBoxParam procedure we would test the value of this variable If it is zero it means that our class wasn t registered We would register our class and set this variable to one so that the next call finds a value different than zero and skips the class regis tration code Libraries 247 We have to tell the IDE to produce a static library now instead of a normal executable file We do this by going into the linker configuration tab and checking the library radio button like this Configuration of Wedit You see the Static library radio button checked The name of the library is the name of the project with the lib extension Now we are ready to change our WinMain We change our WinMain function to be the Get String procedure like this static char buffer 1024 static int classRegistered int APIENTRY GetString char prompt char destbuffer int bufferlen WNDCLASS wc int result HANDLE hinst hinst GetModuleHandle NUI if classRegistered 0 memset amp wc 0 sizeof wc wce lpfnWndProc DefDlgProc wce cbWndExtra DLGWINDOWEXTRA wce hInstance hinst we hCursor LoadCursor NULL IDC_ARROW L wc hbrBackground HBRUSH COLOR_WINDOW 1 wc lpszClassName dialog RegisterClass amp wc classRegistered 1 248 C Tutorial result DialogBoxParam hinst MAKEINTRESOURCE IDD_MAINDIALOG NULL DLGPROC DialogF
83. canceled the operation and to update the progress or activity indicator This is the description of the progress dialog procedure The procedure uses a global variable Cancel to inform the CPU intensive subtask that the user has indicated a desire to terminate the subtask WORD Cancel FALSE This must be global to all modules which call ProgressYield BOOL FAR PASCAL ProgressDlgProc hDlg message wParam lParam HWND hDlg unsigned message WORD wParam DWORD lParam switch message Use other messages to update the progress or activity indicator R case WM_COMMAND switch wParam case ID_CANCEL ID_CANCEL 2 Cancel TRUE default return FALSE default return FALSE The following describes the ProgressYield procedure which should be called after each unit of the CPU intensive subtask is completed The ProgressYield procedure uses the IsDia logMessage function described in the Microsoft Windows Software Development Kit Refer ence Volume 1 IsDialogMessage will convert keyboard messages into selection commands for the corresponding dialog box void ProgressYield HWND hwnd MSG msg Remove all available messages for any window that belong to the current application EJ whil PeekMessage amp msg NULL 0 0 PM_REMOVE Translate and Dispatch the given message if the window handle is null or the given message is no
84. come back to it after calling recursively this function in another dir memset dir 0 sizeof dir getcwd dir sizeof dir 1 This variable holds the current specification we are using q spec First pass We scan here only normal files looping for each of the specifications separated by do Find the first specification Using function pointers 175 p strcehr q Cut the specification at the separator char if p p 0 h FindFirstFile q amp data if h INVALID _HANDLE VALUE do if data dwFileAttributes amp FILE_ATTRIBUTE_DIRECTORY We have found a matching file Call the user s function sprintf fullname s s dir data cFileName if fn fullname return 0 while FindNextFile h amp data FindClose h Restore the input specification It would be surprising for the user of this application that we destroyed the character string that was passed to this function if p p Advance q to the next specification q P while q OK We have done all the files in this directory Now look if there are any subdirectories in it and if we found any recurse hdir FindFirstFile amp dirdata if hdir INVALID_HANDLE_VALUE do if dirdata dwFileAttributes amp FILE_ATTRIBUTE_DIRECTORY This is a directory entry Ignore the and entries if dirdata cFileName 0
85. commands The preprocessor receives its commands with lines beginning with the special character This lines can contain 170 C programming with Icc win32 1 Macros 2 Conditional compilation instructions 3 Pragma instructions 4 The operator 5 Line instructions 1 34 1 1 Preprocessor macros The define command has two forms depending on whether a left parenthesis appears imme diately after the name of the macro The first form without parenthesis is simply the substitu tion of text An example can be define MAXBUFFERSIZE 8192 This means that whenever the preprocessor find the identifier MAXBUFFERSIZE in the pro gram text it will replace it with the character string 8192 The second form of the preprocessor macros is the following define add a b a b This means that when the preprocessor finds the sequence int n add 7 b it will replace this with int n 7 b Note that the left parenthesis MUST be immediately after the name of the macro without any white space blanks tabs in between It is often said that white space doesn t change the meaning of a C program but that is not always true as you can see now If there is white space between the macro name and the left parenthesis the preprocessor will consider that this is a macro with no arguments whose body starts with a left parentheses If you want to delete the macro from the preprocessor table you use the undef lt ma
86. corrected by allowing the implementation to generate a longer string This is a defect because the specification is not self consistent and does not restrict the domain of the argument Suggested Technical Corrigendum Append to 7 23 3 1 2 except that if the value of timeptr gt tm_year is outside the range 2899 8099 and thus the represented year will not fit into four characters it is replaced by up to 4 implementation defined characters Committee Response From 7 1 4 paragraph 1 If an argument to a function has an invalid value such as a value outside the domain of the function or a pointer outside the address space of the program or a null pointer or a pointer to non modifiable stor age when the corresponding parameter is not const qualified or a type after promotion not expected by a function with variable number of arguments the behavior is undefined Thus asctime may exhibit undefined behavior if any of the members of timeptr produce undefined behavior in the sample algorithm for example if the timeptr gt tm_wday is outside the range 0 to 6 the function may index beyond the end of an array As always the range of undefined behavior permitted includes Corrupting memory Aborting the program Range checking the argument and returning a failure indicator e g a null pointer Returning truncated results within the traditional 26 byte buffer There is no consensus to make the suggested change or any change along
87. countchars countchars c 288 We have achieved the first step in the development of a program We have a version of it that in some circumstances can fulfil the specifications that we received 35 There is another construct in this line a comment Commentaries are textual remarks left by the programmer for the benefit of other human readers and are ignored by the compiler We will come back to commentaries in a more formal manner later Input and output 31 But what happens if we just write h lcc examples gt countchars We get the following box that many of you have already seen several times countchars exe Application Error x The instruction at 0x 76415ce referenced memory at 0x68785db4 The memory could not be read Click on OK to terminate the application Click on CANCEL to debug the application Why Well let s look at the logic of our program We assumed without any test that argv 1 will contain the name of the file that we should count the characters of But if the user doesn t sup ply this parameter our program will pass a nonsense argument to fopen with the obvious result that the program will fail miserably making a trap or exception that the system reports We return to the editor and correct the faulty logic Added code is in bold include lt stdio h gt include lt stdlib h gt 1 int main int argc char argv int count 0 chars read FILE infile int c if argc
88. description of the return value and the types of the arguments of a function The general form specifies the return value then the name of the function Then enclosed by parentheses come a comma separated list of arguments with their respective types If the function doesn t have any arguments you should write void instead of the argument list If the function doesn t return any value you should specify void as the return type At each call the compiler will check that the type of the actual arguments to the function is a correct one The compiler cannot guarantee however that the prototypes are consistent across different compilation units For instance if in filel c you declare int fn void then the call fn will be accepted If you then in file2 c you declare another prototype void fn int and then you use fn 6 the compiler cannot see this and the program will be in error crashing mysteriously at run time This kind of errors can be avoided if you always declare the prototypes in a header file 60 C programming with Icc win32 that will be included by all files that use that function Do not declare prototypes in a source file if the function is an external one 1 13 18 Const Constant values can t be modified The following pair of declarations demonstrates the differ ence between a variable pointer to a constant value and a constant pointer to a variable value const int ptr_to_constant
89. do this for you and we need to process the WM_DRAWITEM message Windows sends us a pointer to a DRAWITEMSTRUCT that contains all the necessary information to do the draw ing in the LPARAM parameter This structure is defined as follows Member Description unsigned int CtlType This member can be one of the following values ODT_BUTTON button ODT_COMBOBOX combo box ODT_LISTBOX list box ODT_LISTVIEW List view control ODT_MENU Owner drawn menu item ODT_STATIC static control ODT_TAB Tab control unsigned int Ctl1lID Specifies the identifier of the combo box list box button or static con trol This member is not used for a menu item unsigned int itemID Specifies the menu item identifier for a menu item or the index of the item in a list box or combo box For an empty list box or combo box this member can be 1 This allows the application to draw only the focus rectangle at the coordinates specified by the rcItem member even though there are no items in the control unsigned int itemAction Specifies the drawing action that windows expect us to perform This action is indicated with the following flags ODA_DRAWENTIRE The entire control needs to be drawn ODA_FOCUS The control has lost or gained the keyboard focus The itemState member should be checked to determine whether the control has the focus ODA_SELECT The selection status has changed The itemState mem ber should be checked to determine the new sele
90. filling band RECT rectClient Rectangle for entire client area float fStep How large is each band HBRUSH hBrush int iOnBand Loop index How large is the area you need to fill GetClientRect hWnd amp rectClient Determine how large each band should be in order to cover the client with 256 bands one for every color intensity level fStep float rectClient bottom 256 0f Start filling bands for iOnBand 0 iOnBand lt 256 iOnBand Set the location of the current band SetRect amp rectFill 0 Upper left X int iOnBand fStep Upper left Y rectClient right 1 Lower right X int iOnBand 1 Step Lower right Y Create a brush with the appropriate color for this band hBrush CreateSolidBrush RGB 0O 0 255 iOnBand Fill the rectangle FillRect ADC amp rectFill hBrush Get rid of the brush you created DeleteObject hBrush Give back the DC ReleaseDC hWnd hDC 358 C Tutorial 2 22 6 How do I calculate print margins An application can determine printer margins as follows Calculate the left and top margins e Determine the upper left corner of the printable area calling GetDeviceCaps with the PHYSICALOFFSETX and PHYSICALOFFSETY indices For example Init our pt struct in case escape not supported pt x 0 pt y 0 Locate the upper left corner of the printable area pt x GetDeviceCaps hPrnDC PHYSICALOFFS
91. handle and exit returning the number of matches Now having setup the framework here is the function that process each file static int processfile regexp expression char filename FILE f fopen filename r int namewritten 0 int matches 0 int line 1 char buf 8192 if f NULL return 0 while fgets buf sizeof buf f if regexec expression buf 212 C programming with Icc win32 matches if namewritten printf s n filename namewritten 1 printf 4d s line buf linet fclose f return matches No secrets here We open the file and read each line of it using fgets To each line we apply our regular expression and if there is a match we print that line We print the file name before printing any matches to separate the matches from one file from the matches of the next file in the output We always write the line number and we loop until there are no more lines Note that the test for failure to open the file is maybe unnecessary because we are certain that the file exists since the name is the result of a _findfirst or a _findnext It could be however that the file exists but it is not accessible because it is being used by another program in exclu sive mode or that the access rights are such that we can t read it It is better to avoid crashes so a simple test doesn t make our program much fatter Programming with security in mind 213
92. here The rest is a matter of read ing the docs to find out which events you can handle for each object in the dialog and writing the called functions with the help of the windows documentation But what happens if there is an event that is not foreseen by the framework With most frame works this is quite a problem happily not here You have just to check the button Al in the dialog properties and the framework will generate a call to a default procedure named lt pre fix gt Default at each message There you can handle all events that the operating system sends I have tried to keep the framework open so that unforeseen events can be still treated correctly Another way to customize the framework is to modify the default procedure provided in the library weditres lib The source of that procedure is distributed in the source distributions of 133 Icc win and is relatively easy to modify 133 To find that easily just press F12 and click in its name in the function list 300 C Tutorial 2 14 Customizing controls Under windows you have a set of building blocks at your disposal that is even it is quite rich fixed A plain listbox will look like a listbox and there is no obvious way to modify the appearence of it not even for doing such simple things like writing the text in red or painting the background in brown The reason for this is simple there are infinitely many ways of customizing a control and if Windows
93. html Types 17 3 1 2 1 Pointer to function 3 1 2 2 Pointer to object types 3 1 2 3 Pointer to incomplete types 3 2 Non scalar types 3 2 1 Struct types 3 2 2 Union types 3 2 3 Array types 1 6 3 Integer types The language doesn t specify exactly how big each integer type must be but it has some requirements as to the minimum values a type must be able to contain hence its size The char type must be at least 8 bits the int type must be at least 16 bits and the long type must be at least 32 bits How big each integer type actually is is defined in the standard header limits h for each implementation 1 6 4 Floating types Floating types are discussed in more detail later Here we will just retain that they can repre sent integer and non integer quantities and in general their dynamic range is bigger that inte gers of the same size They have two parts a mantissa and an exponent As a result there are some values that can t be expressed in floating point for instance 1 3 or 1 10 This comes as a surprise for many people so it is better to underscore this fact here More explanations for this later on Floating point arithmetic is approximate and many mathematical laws that we take for granted like a b a is equal to b do not apply in many cases to floating point math 1 6 5 Compatible types There are types that share the same underlying representation For instance in Icc win for the Intel platform in 32 bits
94. i 0 i lt maxit i 1 theta double i CENTER r scale exp theta tan in if r gt cut break x r cos theta CENTER y r sin theta CENTER d randx double rand double RAND_MAX randy double rand double RAND_MAX PlotDotAt hDC xt f randx y f randy RGB 0 0 0 OAarANa oF WN sate for int i 0 i lt maxit i theta double i CENTER theta2 double i CENTER 3 14 r scale exp theta2 tan in 9 if r gt cut break x r cos theta CENTER y r sin theta CENTER randx double rand double RAND_MAX randy double rand double RAND_MAX PlotDotAt hDC xt f randx y f randy RGB 255 0 0 10 We translate both loops into two for statements The exit from those loops before they are fin ished is done with the help of a break statement This avoids the necessity of naming loops when we want to break out from them what could be quite fastidious in the long term I suppose that in the language the author is using loops go until the variable is equal to the number of iterations Maybe this should be replaced by a strictly smaller than but I do not think a point more will do any difference Note the cast of i double i Note too that I always write 50 0 instead of 50 to avoid unnecessary conversions from the integer 50 to the floa
95. i d n i return 0 The output of this program is outer i is 0 i 0 i 1 outer i is 1 i 0 i 1 Note that the scope of the identifiers declared within a for scope ends just when the for state ment ends and that the for statement scope is a new scope Modify the above example as follows to demonstrate this include lt stdio h gt int main void for int i 0 i lt 2 it 1 printf outer i is d n i 2 int i 87 for int i 0 i lt 2 itt 4 printf i d n i 5 6 7 return 0 8 14 C programming with Icc win32 At the innermost loop there are three identifiers called 1 The first i is the outer i Its scope goes from line 1 to 7 the scope of the for statement eThe second i 87 is a local identifier of the compound statement that begins in line 1 and ends in line 7 Compound statements can always declare local variables eThe third i is declared at the innermost for statement Its scope starts in line 4 and goes up to line 6 It belongs to the scope created by the second for statement Note that for each new scope the identifiers of the same name are shadowed by the new ones as you would normally expect in C When you declare variables in the first part of the for expression note that you can add state ments and declarations but after the first declaration only declarations should follow For instance if you have struct f int a b struct f StructF for StructF
96. identifiers that are defined within the block A block scope can nest other blocks The function prototype scope is the list of parameters of a function Identifiers declared within this scope are visible only within it Let s see a concrete example of this static int Counter 780 file scope extern void fn int Counter function prototype scope void function int newValue int Counter Block scope double d newValue label for int i 0 i lt 10 it if i lt newValue char msg 45 int Counter 78 sprintf msg i d n i Counter if i 4 goto label At the point indicated by the arrow the poor Counter identifier has had a busy life 66 An identifier can also represent a macro or a macro argument but here we will assume that the pre processor already has done its work 67 You see the infinite loop here Tell me why is this loop never ending Look at the code again Top down analysis 121 e It was bound to an integer object with file scope e Then it had another incarnation within the function prototype scope e Then it was bound to the variables of the function setCounter as a parameter e That definition was again shadowed by a new definition in an inner block as a local variable The value of Counter at the arrow is 78 When that scope is finished its value will be the value of the parameter called Counter within the function function
97. illustrates steps a through c Get the size of the printable area pt x GetDeviceCaps hPrnDC PHYSICALWIDTH pt y GetDeviceCaps hPrnDC PHYSICALHEIGHT xOffsetOfRightMargin xOffset GetDeviceCaps hPrnDC HORZRES Pex GetDeviceCaps hPrnDC LOGPIXELSX wInchesWeWant yOffsetOfBottomMargin yOffset GetDeviceCaps hPrnDC VERTRES pt y GetDeviceCaps hPrnDC LOGPIXELSY winchesWeWant NOTE Now you can clip all output to the rectangle bounded by xOffset yOffset xOffsetOf RightMargin and yOffsetOfBottomMargin 2 22 7 How do calculate the bounding rectangle of a string of text Get a bounding rectangle for a string of text output to a specified coordinate in a DC using the currently selected font NOTE The reference DC must have a True Type font selected FAQ 359 BOOL GetTextBoundingRect HDC hDCc Reference DC int X X Coordinate int Y Y Coordinate LPSTR lpStr The text string to evaluate DWORD dwhen The length of the string LPRECT lprc Holds bounding rectangle LPPOINT lpPoints iPBYTE lpTypes int i iNumPts Draw the text into a path BeginPath hDC i SetBkMode hDC TRANSPARENT TextOut hDC x y lpStr dwlLen SetBkMode hDC i EndPath hDC How many points are in the path iNumPts GetPath hDC NULL NULL 0 if iNumPts 1 return FALSE Allocate room for the point
98. infile gt file while c EOF count if c gt Frequencies c Frequency c fgetc infile gt file return count Instead of reading directly from the infile argument we use the file member of it That s all Note that infile is a pointer so we use the notation with the arrow instead of a point to access the file member of the structure But there is something wrong with the name of the function It wrongly implies that we are processing a FILE instead of a stream Let s change it to ProcessStream and change the name of the stream argument to instream to make things clearer int ProcessStream STREAM instream CHARS Frequencies int count 0 int c fgetc instream gt file while c EOF count if c gt Frequencies c Frequency c fgetc instream gt file return count This looks cleaner Now we have to change our main function to make it read all the files that match the given name Our new main procedure looks like this int main int argc char argv int count 0 STREAM infile checkargs argc argv if infile NULL return 1 Initialize do count ProcessStream infile Frequencies fclose infile gt file Extending a program 127 infile GetNext infile while infile 0 printf d chars in file n count qsort Frequencies 256 sizeof CHARS compare DisplayOut
99. information about a resource such as its size and type or can be some or all of the resource itself The part of a response that includes some or all of the requested resource is called the response data or the entity body and the response is not complete until all the response data is received 3 3 1 GetHttpUrl The interface for our function should be as simple as possible It will receive two character strings representing the name of the URL to retrieve and the name of the output file where the file should be stored If you are interested in using the resulting code you can skip this sec tion We start by opening an http session The general schema for an http session is like this WinHttpOpen WinHttpConnect WinHttpOpenRequest WinHttpSetCredentials WinHttpSendRequest WinHttp WriteD ata WinHttpReceiveResponse WinHttpQueryData4vailable WinHttpQueryHeaders WinHttp Query AuthSchemes WinHttpCloseHandle Clasic We open a session connect and send requests In this case we are concerned only with retrieving the data i e a GET request WinHttpReadD ata We do then an open we connect and start a request for a resource We read from the headers some info before we read the data it would be nice to check that the resource actually exists and accordingly we read the content of the file or not 390 C Tutorial 3 3 2 Implementation We open a session using the WinHttpOpen API hSessi
100. is useful for detecting memory leaks Suppose you want to make sure a new operation you have just added to your software doesn t leak any memory You just do int mem AllocatedMemory result newOperation parml parm2 if mem AllocatedMemory Here we have detected a memory leak 1 30 8 1 Improving allocate release Of course with this simple code we have just scratched the surface of this problem Several issues are more or less immediately visible 1 We have assumed in our code that there are no alignment problems i e that we can access an integer at any memory address This is not true for many processor that have strict alignment requirements and need to be feeded aligned integers with catastrophic failures if they are not We need to align the start pointer that we return to the user of our allocation functions and we need to align the MAGIC number at the end of the block One portable way to do this is to make a alignment union like this that gives us the alignment requirement union __altypes char c short s int i long long 11 long double 1d AllTypes Memory management strategies 151 2 It may be a better idea to destroy all data in the released block to avoid it being used by mistake later in the program For instance if we set all data to zero any usage of pointers within the released block would trap 3 We could store all allocated block addresses somewhere and make a heap check
101. item we are interested only in the PARAM part of the item More complicated is the procedure for querying the window for information Here is a simple approach void SetTextInStatusBar HWND hParent HWND hwnd RECT rc HANDLE pid char info 4096 pProcessName GetWindowRect hwnd amp rc GetWindowThreadProcessId hwnd amp pid pProcessName PrintProcessNameAndID ULONG pid wsprintf info Handle Ox x Ss left Sd top d right d bottom d height Sd width d Process s hwnd IsWindowVisible hwnd Visible Hidden rc left rc top rc right rc bottom rce bottom rc top re right rc left pProcessName UpdateStatusBar info 0 0 The algorithm here is as follows Query the window rectangle in screen coordinates We get the process ID associated with this window We call a subroutine for putting the name of the process executable file given its process ID We format everything into a buffer We call UpdateStatusBar generated by wedit with this character string we have built The procedure for finding the executable name beginning with a process ID is quite advanced and here we just give it like that static char PrintProcessNameAndID DWORD processID 280 C Tutorial static char szProcessName MAX_PATH HMODULE hMod DWORD cbhNeeded HANDLE hProcess OpenProcess PROCESS_QUERY_INFORMATION PROCESS_VM_READ FALSE processID szProcessName 0 0 if hPr
102. itself i e list and element are the same object their addresses are identical we refuse This is an error in most cases but maybe you would need a circular element list of one element In that case just eliminate this test Note that Insert list NULL will effectively cut the list at the given element since all elements after the given one would be inaccessible Many other functions are possible and surely necessary They are not very difficult to write the data structure is quite simple Double linked lists have two pointers hence their name a Next pointer and a Previous pointer that points to the preceding list element Our data structure would look like this typedef struct _dlList struct _dlList Next struct _dlList Previous Using structures continued 165 void data DLLIST Our Append function above would look like new material in bold LIST AppendD1 DLLIST pListRoot void data DLLIST rvp pListRoot is the list empty if rvp NULL Yes Allocate memory pListRoot rvp GC_malloc sizeof DLLIST rvp gt Previous NULL else find the last element while rvp gt Next rvp rvp gt Next Add an element at the end of the list rvp gt Next GC_malloc sizeof DLLIST rvp gt Next gt Previous rvp rvp rvp gt Next initialize the new element rvp gt Next NULL rvp gt Data data return rvp The Insert fu
103. keybd_event VK_NUMLOCK 0 KEYEVENTF_EXTENDEDKEY 382 C Tutorial 0 Simulate a key releas keybd_event VK_NUMLOCK EYEVENTF_EXTENDEDKEY KEYEVENTF_KEYUP i ONO int main void SetNumLock TRUE To send key strokes to a window you give the focus to the window or control using the SetFo cus API then you simulate the keyboard events you want 2 22 33 How can I encrypt and decrypt a character string The easiest way is to use the String library of lcc win containers lib Using that it is just a matter of include lt strings h gt include lt stdio h gt int main void String s Security is our business Strencrypt s Strdecrypt s printf s n s content If you want to stay within the C framework only here is the code for encrypting and decrypt ing a string You should change the interface of course For the purposes of this function a String is a structure with a count and a pointer to the contents include lt windows h gt include lt wincrypt h gt int Strdecrypt String amp src HCRYPTMSG hMsg unsigned int cbDecoded char pbDecoded this variables should be changed to some parameters if you want to change the interface of this function cbEncodedBlob should contain the length of the blob and ppbEncodedBlob should point to the start of it unsigned cbEncodedBlob Strl
104. lt 2 2 printf Usage countchars lt file name gt n exit EXIT FAILURE 3 infile fopen argv 1 r c fgetc infile while c EOF count c fgetc infile printf d n count return 0 1 We need to include lt stdlib h gt to get the prototype declaration of the exit function that ends the program immediately 2 We use the conditional statement if to test for a given condition The general form of it is if condition statements else statements 3 We use the exit function to stop the program immediately This function receives an integer argument that will be the result of the program In our case we return the error code 1 The result of our program will be then the integer 1 Note that we do not use the integer constant 1 directly but rather use the predefined constants EXIT_SUCCESS defined as 0 or 36 This is the display under Windows NT In other systems like Linux for instance you will get a Bus error core dumped message 32 C programming with Icc win32 EXIT_FAILURE defined as 1 in stdlib h In other operating systems or environments the numeric value of EXIT_FAILURE could be different By using those predefined constants we keep our code portable from one implementation to the other Now when we call countchars without passing it an argument we obtain a nice message h lcc examples gt countchars Usage countchars lt fil
105. many instructions that adjust the stack after the function call are not needed and replaced by a single instruction at the end of the called function Functions with this type of calling convention will be internally decorated by the compiler by adding the stack size to their name after an sign For instance a function called fn with an integer argument will get called fn 4 The purpose of this decorations is to force the pre vious declaration of a stdcall function so that always we are sure that the correct declarations was seen if not the program doesn t link 1 13 24 Break and continue statements The break and continue statements are used to break out of a loop or switch or to continue a loop at the test site They can be explained in terms of the goto statement while condition 0 doSomething if condition 0 break doSomethingE1se is equivalent to while condition 0 doSomething if condition 0 goto labl doSomethingEl1se lab1 The continue statement can be represented in a similar way while condition 0 doSomething if condition 25 continue doSomethingEl1se is equivalent to restart while condition 0 doSomething if condition 25 goto restart doSomethingEl1se The advantage of avoiding the goto statement is the absence of a label Note that in the case of the for statement execution continu
106. memory location for an integer variable that will hold the current argument to be printed This is a local variable i e a variable that can only be used within the enclosing scope in this case the scope of the function main Local variables are declared as any other variables with lt type gt identifier For instance int a double b char c Arrays are declared in the same fashion but followed by their size in square brackets int a 23 double b 45 char c 890 3 We use the for construct i e an iteration The for statement has the following structure e Initialization Things to be done before the loop starts In this example we set the counter to zero We do this using the assign statement of C the sign The general form of this statement is 669 e variable value e Test Things to be tested at each iteration to determine when the loop will end In this case we test if the count is still smaller than the number of arguments passed to the program the integer argc e Increment Things to be updated at each iteration In this case we add 1 to the counter with the post increment instruction counter This is just a shorthand for writing counter counter 1 e Note that we start at zero and we stop when the counter is equal to the upper value of the loop Remember that in C array indexes for an array of size n elements always start at zero and run until n 1 29 4 We use again pr
107. message the main window procedure will receive a WM_SIZE message and we will handle the sizing 126 In page 218 Published by St Martin s Press 1990 ISBN 0 312 06179 X pbk 274 C Tutorial of the tree control there This has the advantage that it will work when the user resizes the main window too 2 10 2 Moving and resizing the child windows We add code to the WM_SIZE message that Wedit already had there to handle the resizing of the status bar at the bottom of the window LRESULT CALLBACK MainWndProc HWND hwnd UINT msg WPARAM wParam LPARAM lParam static HWND hwndTree RECT rc rcStatus switch msg case WM_CREATE hwndTr CreateTr hwnd IDTREEWINDOW break case WM_SIZE SendMessage hWndStatusbar msg wParam lParam InitializeStatusBar hWndStatusbar 1 GetClientRect hwnd amp rc GetWindowRect hWndStatusbar amp rcStatus re bottom rcStatus bottom rcStatus top MoveWindow hwndTree 0 0 rc right rc bottom 1 break We ask windows the current size of the main window with Get ClientRect This proce dure will fill the rectangle passed to it with the width and height of the client area i e not con sidering the borders title menu or other parts of the window It will give us just the size of the drawing surface We have a status bar at the bottom and the area of the status bar must be subtracted from the total area We query this t
108. most customers the UpdateBalance field empty filled with a NULL pointer and the global UpdateBalance procedure will use that field to calculate its results only if there is a procedure there to call True this wastes 4 bytes per cus tomer in most cases since the field is mostly empty but this is a small price to pay the struc ture is probably much bigger anyway 1 20 2 Structure size In principle the size of a structure is the sum of the size of its members This is however just a very general rule since it depends a lot on the compilation options valid at the moment of the structure definition or in the concrete settings of the structure packing as specified with the pragma pack construct Normally you should never make any assumptions about the specific size of a structure Com pilers and Icc win is no exception try to optimize structure access by aligning members of the structure at predefined addresses For instance if you use the memory manager pointers must be aligned at addresses multiples of four if not the memory manager doesn t detect them and that can have disastrous consequences The best thing to do is to always use the sizeof operator when the structure size needs to be used somewhere in the code For instance if you want to allocate a new piece of memory managed by the memory manager you call it with the size of the structure 64 This pragma allows the user to control the sructure layout 114
109. n1 q n w n1 t n d rw i nl n n r w r ne nl 1 K rw ik nl wi q n wk nw iwk KK nl w S l w i n1 q ld r nlwb de c i dnl rw nc nw tkd e rdq w nr xrl n t lt 50 _ a putchar 31 a main 65 _ at 1 main a t _ a 1 0 lt t main 2 2 s a main 0 main 61 a lek dce i bK q w n r3 1 nuwloca O m vpbks fxntdCeghiry a 1 1 4 3 Tatoo This one is in the obfuscated C contest More of this kind of stuff at the URL http www ioccc org int i main for i lt i i i read it hell o world n read j i p write j ptp i j i i Bibliography 225 1 5 Bibliography Here are some books about C I recommend you to read them before you believe what I say about them C Unleashed Richard Heathfield Lawrence Kirby et al Heavy duty book full of interesting stuff like structures matrix arithmetic genetic algorithms and many more The basics are covered too with lists queues double linked lists stacks etc Algorithms in C Robert Sedgewick I have only the part 5 graph algorithms For that part that covers DAGs and many others I can say that this is a no nonsense book full of useful algorithms The code is clear and well presented C a reference manual Fifth edition Samuel P Harbison Guy L St
110. network program By getting the count of the packets trans mitted connections etc you can measure exactly how is the performance of your network application 3 6 Writing ping Ping is a small program that attempts to send an echo request to another machine If the response arrives the other machine is up and running if not well there is a problem with the physical connection somewhere or the other machine is down Simple Lcc win provides a ping function that can be used to ping a host under program control To use that it is just necessary to include the ping h header file The simplest program using ping can be written like this include lt ping h gt include lt stdio h gt int main int argc char argv PingInterface p memset amp p 0 sizeof p p HostName argv l1 if ping amp p printf Host s is up n argv 1 else printf Host s is down n argv 1 3 6 1 How does it work The algorithm followed by the implementation of ping is to open a connection a socket using the raw state i e without using any higher level protocol not even the TCP protocol Using this socket we write an ICMP packet Internet Control Management Protocol into the buffer we are going to send and we wait for the answer When the answer arrives we record how much time it took for the packet to make the round trip Writing ping 399 It sounds simple b
111. number FE_STACKFAULT The floating point stack has overflowed The denormal flag means that a loss of precision is certain the number is too small to be rep resented The stack fault flag means that lcc win generated bad code since all floating point 88 The round functions round their argument to the nearest integer value in floating point format round ing halfway cases away from zero regardless of the current rounding direction Ansi C standard page 232 89 The C standard paragraph 7 6 204 C programming with Icc win32 operations should balance the floating point stack If you ever test positive for this flag do not hesitate to send me a bug report In general the floating point flags can be queried by the program to know if the last operation did complete without problems Here is a small example to show you how this works This program tests a division by zero include lt fenv h gt include lt stdio h gt int main void double a 1 b 0 feclearexcept FE_DIVBYZERO a a b if fetestexcept FE_DIVBYZERO printf You have divided by zero n return 0 First we clear the flag that we are going to use using feclearexcept Then we perform our operation and query if the flag is set using fetestexcept Since we know that the flags are set but not cleared the expression could be very well be a much more complicated sequence of operations The above code would work the same bu
112. objects that have a natural order You can go from a given list member to the next element or to the previous one We have several types of lists the simplest being the single linked list where each member contains a pointer to the next element or NULL if there isn t any We can implement this structure in C like this typedef struct _list struct _list Next Pointer to next element void Data Pointer to the data element LIST We can use a fixed anchor as the head of the list for instance a global variable containing a pointer to the list start LIST Root We define the following function to add an element to the list LIST Append LIST pListRoot void data LIST rvp pListRoot if rvp NULL is the list empty Yes Allocate memory pListRoot rvp GC_malloc sizeof LIST else find the last element while rvp gt Next rvp rvp gt Next Add an element at the end of the list rvp gt Next GC_malloc sizeof LIST rvp rvp gt Next initialize the new element rvp gt Next NULL rvp gt Data data return rvp This function receives a pointer to a pointer to the start of the list Why If the list is empty it needs to modify the pointer to the start of the list We would normally call this function with newElement Append amp Root data Note that loop while rvp gt Next 164 C programming with Icc win32 rvp rvp gt Next This mean
113. of elements in the array corresponded to a character value But once we sort the array this ordering is gone and we have lost the correspondence between each array element and the character it was representing C offers us many solutions to this problem but this is taking us too far away from array han dling the subject of this section We will have to wait until we introduce structures and user types before we can solve this problem 1 18 2 Other qsort applications Suppose you have a table of doubles and you want to get an integer vector holding the indexes of each double precision number in a sorted vector The solution is to make a comparison function that instead of looking at the double array to make its decision receives the indexes vector instead and looks in the values array We establish two global variables 1 a values array holding the double precision data and 2 an indexes array holding the integer indices This are global variables since they should be accessible to the callback function whose inter face is fixed we can t pass more arguments to the comparison function We arrive then at the following program include lt stdio h gt include lt stdlib h gt define N 100 The size of the array 106 C programming with Icc win32 double values N int indexes N This comparison function will use the integer pointer that it receives to index the global values array Then the comparison is do
114. of the loop it will print the totals int main void long long BytesAvailable TotalBytesAvailable 0 long long capacity TotalCapacity 0 long long userFree TotalUserFree 0 long long used TotalUsed 0 long double percent int counter C Start with C drive ignoring floppies char diskname 512 strcpy diskname C printf 6s 15s 15s 15s 6s n Drive Capacity Available Used Free while counter 1 Z diskname 0 counter if GetDiskFreeSpaceEx diskname amp BytesAvailable amp capacity amp userFree percent 100 0L long double BytesAvailable long double capacity used capacity BytesAvailable r printf formats 6s format string in 6 position left justified negative width 15 lld format 64 bit in 15 positions separating digits in groups 6 2Lf format long double Lf in 6 positions with 2 decimals i printf 6s 15 1lld 15 lld 15 11d 6 2L n diskname capacity BytesAvailable used percent TotalBytesAvailable BytesAvailable TotalCapacityt capacity TotalUsed used counter Now print the totals percent 100 0L long double TotalBytesAvailable long double TotalCapacity printf n 6s 15 lld 15 1lld 15 lld 6 2L n Total TotalCapacity TotalBytesAvailable TotalUsed percent return 0 The output of this program can look
115. or a bitmap The following code shows one way to implement a splash screen window define SZ_INIT EXT Initializing application define SZ_LOAD EXT Loading resources define SZ_CLOSE EXT Closing splash window define SZ_SPLASH EXT Splash window define ID_TIMER_CLOSE0x1111 define ID_TIMER_INIT0x1112 define ID_TIMER_LOAD0x1113 define ID_TIMER_DONE0x1114 ATOM MyRegisterClass HINSTANCE hInstance BOOL InitInstance HINSTANCE hInstance int nCmdShow LRESULT CALLBACK WndProc HWND hWnd UINT message WPARAM wParam LPARAM lParam HINSTANCE hInst NULL TCHAR SplashWndClass 28 int APIENTRY WinMain HINSTANCE hInstance HINSTANCE hPrevinstance LPSTR lpCmdLine int nCmdShow MSG msg lstrcpy SplashWndClass TEXT SplashWindow MyRegisterClass hInstance Perform application initialization if InitInstance hInstance nCmdShow return FALSI Gl Main message loop while GetMessage amp msg NULL 0 0 TranslateMessage amp msqg DispatchMessage amp msg return msg wParam FUNCTION MyRegisterClass PURPOSE Registers the window class COMMENTS This function and its use is only necessary if you want this code to be compatible with Win32 systems prior to the 362 C Tutorial
116. or decrement of a position If we pass to qsort an array of 56 double preci sion numbers this argument will be 8 i e the size of a double precision number and the preceding argument will be 56 i e the number of elements in the array Argument 4 is a function int f const void Well this is quite hard really We are in the first pages of this introduction and we already have to cope with gibberish like this We have to use recursion now We have again to start reading this from left to right more or less We have a function pointer f that points to a function that returns an int and that takes as arguments a void i e a pointer to some unspecified object that can t be changed within that function const This is maybe quite difficult to write but quite a powerful feature Functions can be passed as arguments to other functions in C They are first class objects that can be used to specify a function to call Why does qsort need this Well since the qsort function is completely general it needs a helper function that will tell it when an element of the array is smaller than the other Since qsort doesn t have any a priori knowledge of the types of the elements of the passed array it needs a helper function that returns an integer smaller than zero if the first element is smaller than the next one zero if the elements are equal or bigger than zero if the elements are bigger Let s apply this to a smaller exampl
117. own vir tual keyboard and mouse driver to receive these keyboard and mouse events To optimize performance it is good practice for applications to detect whether they are run ning in a Terminal Services client session For example when an application is running on a remote session it should eliminate unnecessary graphic effects like 1 Splash screens Transmitting a splash screen to a Terminal Services client consumes extra network bandwidth and forces the user to wait before accessing the application 2 Animations which consume CPU and network bandwidth 3 Direct input or output to the video display You can detect if you are running in a remote session by using the following code BOOL IsRemoteSession void return GetSystemMetrics SM_REMOTESESSION 2 17 15 Windows Here is a short overview of the types of controls available to you Etc 321 Control Description Edit Single or multi line text editor Checkbox For a set of multiple choices Listbox For displaying lists Combobox A list an edit control Static Group boxes static text filled rectangles Used for labels grouping and separation Push buttons Used to start an action Radio buttons Used for choosing one among several possible choices Scroll bars Used for scrolling a view Animation controls Display AVI files Date and Time Used to input dates Headers Allow the user t
118. parameter passed to each function is a handle to an open key This key must be opened before the function call and closed afterward QueryKey Enumerates the subkeys of key and the associated _ values then copies the information about the keys and values into a pair of edit controls and list boxes hDig Dialog box that contains the edit controls and list boxes hKey Key whose subkeys and values are to be enumerated void QueryKey HWND hDlg HANDLE hKey CHAR achKey MAX_PATH CHAR achClass MAX_PATH buffer for class name DWORD cchClassName MAX_PATH size of class string DWORD cSubKeys number of subkeys DWORD cbMaxSubKey longest subkey size DWORD cchMaxClass longest class string DWORD cValues number of values for key DWORD cchMaxValue longest value name DWORD cbMaxValueData longest value data DWORD cbhSecurityDescriptor size of security descriptor FILETIME ftLastWriteTime last write time DWORD i j DWORD retCode retValue CHAR achValue MAX_VALUE_NAME DWORD cchValue MAX_VALUE_NAME CHAR achBuff 80 Get the class name and the value count RegQuerylInfokey hKey key handle achClass buffer for class name amp cchClassName size of class string NULL reserved 310 C Tutorial amp cSubKeys number of subkeys amp cbMaxSubKey longest subkey size amp cch
119. parts Now suppose that we want to handle several files With this organization it is straightforward to arrange for this in a loop ProcessFile receives an open FILE and a Frequencies array both can be easily changed now A modular program is easier to modify than a monolithic one We see too that the function that process the files leaves them open We could streamline more main if we got rid of that in the ProcessFile function but I find it personally better that the same function that opens a file closes it too so that the reader can see if the fopen fclose calls match 1 24 Extending a program Let s suppose then that we want to investigate all frequencies of characters in a directory choosing all files that end in a specific extension for instance c In principle this is easy we pass to ProcessFile a different open file each time and the same Frequencies array We develop a GetNextFile function that using our c character string will find the first file that meets this name specifications foo c for example and then will find all the other files in the same directory that end with a c extension How do we do this Well looking at the documentation we find that we have two functions that could help us findfirst and findnext The documentation tells us that findfirst has a prototype like this long findfirst char spec struct _finddata_t fileinfo This means that it receives a pointer to
120. pass a non zero terminated string to this apparently harmless routine you activate a randomly firing machine gun that will start destroying your program s data in a random fashion The absence of a zero byte in a string is fatal for any C program In a tutorial this can t be too strongly emphasized 1 17 6 paste You have got two text files and you want to merge them in a single file separated by tabula tions For instance if you have a filel with this contents line 1 line2 and you got another file2 with this contents line 10 line 11 you want to obtain a file linel line 10 line 2 line 11 Note that both file can be the same A solution for this could be the following program include lt stdio h gt include lt string h gt 55 If remembering which headers contain which definitions bothers you as it bothers me just use the lt stdheaders h gt header file included with Icc win That file is just an include of all standard header files 94 C programming with Icc win32 include lt stdlib h gt ii We decide arbitrarily that lines longer than 32767 chars will make this program fail define MAXLINELEN 32767 int main int argc char argv J We need two FILE pointers and two line buffers to hold each line from each file We receive in argc the number of arguments passed 1 and in the character array argv the names of the two files FILE 1 2 char buf1 MAXLINELEN bu 2 MAXLINELEN
121. piece of software to read a textual representation first translating it directly into a sequence of numbers that the printed circuit understands This is optionally done by assembling several pieces of the program together as a unit 1 3 5 3 Runtime The operating system loads the prepared sequence of instructions from the disk into main memory and passes control to the entry point This is done in several steps First the main executable file is loaded and then all the libraries the program needs When everything has been mapped in memory and all the references in each part have been resolved the OS calls the initialization procedures of each loaded library If everything goes well the OS gives control to the program entry point An overview of the standard libraries 9 1 4 An overview of the standard libraries These headers and the associated library functions are found in all C99 compliant compilers Header Purpose assert h Diagnostics for debugging help complex h Complex numbers definitions See page 206 ctype h Character classification isalpha islower isdigit ermo h Error codes set by the library functions fenv h Floating point environment Functions concerning the precision of the calculations exception handling and related items See page 192 float h Characteristics of floating types float double long double qfloat See page 192 inttype
122. port and passive mode We pass NULL as user name and password This means that we always use the anonymous login 394 C Tutorial hConnect InternetConnect hOpen host INTERNET_INVALID_PORT_NUMBER NULL NULL INTERNET_SERVICE_FTP INTERNET_FLAG_ PASSIVE 0 if hConnect OK We arrive at the interesting part We retrieve the file using INTERNET_FLAG_RELOAD what means a download is forced of the requested file object or directory listing from the origin server not from the cache Besides this we always use binary mode for all transfers 41 fret FtpGetFil hConnect infile outfile FALSE Do not fail if local file exists INTERNET_FLAG_ RELOAD FTP_TRANSFER_TYPE_BINARY 0 if fret 0 fret GetLastError else fret 0 Cleanup InternetCloseHandl hConnect else fret GetLastError InternetCloseHandle hOpen return fret int main void return GetFtpUrl ftp cs virginia edu pub lcec win32 README README To give you an idea when the first FTP protocol implementations under windows 3 0 were monster programs of several thousand lines Of course those thousands of lines are still there in the code of those FtpGetFile primitives The advantage is that you do not have to worry about it To link this program you should use the wi
123. pre processor The first phase of the compilation process is the pre processing phase This consists of scan ning in the program text all the preprocessor directives i e lines that begin with a charac ter and executing the instructions found in there before presenting the program text to the compiler We will interest us with just two of those instructions The first one is the define directive that instructs the software to replace a macro by its equivalent We have two types of macros Parameterless For example define PI 3 1415 Following this instruction the preprocessor will replace all instances of the identifier PI with the text 3 11415 Macros with arguments For instance define s2 a b a a b b 2 0 When the preprocessor finds a sequence like s2 x y It will replace it with x x y y 2 0 The problem with that macro is that when the preprocessor finds a statement like S2 x 6 0 y 4 8 It will produce x 6 0 x 6 0 yt 6 0 y 6 0 2 0 What will calculate completely another value 7 0 x 7 0 y 12 0 2 0 To avoid this kind of bad surprises it is better to enclose each argument within parentheses each time it is used define s2 a b a a b b 2 0 This corrects the above problem but we see immediately that the legibility of the macros suf fers quite complicated to grasp with all those redundant parentheses around Another problem arises when you wa
124. process void int error_code if error_happened long jmp ErrorEnv error_code With all respect I have for Harbison and Steele and their excellent book this example shows how NOT to use setjmp longjmp The ErrorEnv global variable is left in an undefined state after the function exits with zero When you use this facility utmost care must be exercised to avoid executing a longjmp to a function that has already exited This will always lead to catastrophic consequences After this function exists with zero the contents of the global ErrorEnv variable are a bomb that will explode your program if used Now the process function is entirely tied to that variable and its validity You can t call process from any other place A better way could be include lt set jmp h gt jmp_buf ErrorEnv int guard void Return 0 if successful else longjmp code jmp_buf pushed_env memcpy push_env ErrorEnv sizeof jmp_buf int status set jmp ErrorEnv if status 0 process memcpy ErrorEnv pushed_env sizeof jmp_buf return status 86 C programming with Icc win32 int process void int error_code 0 if error_code longjmp ErrorEnv error_code This way the contents ErrorEnv are left as they were before and if you setup in the first lines of the main function int main void if set jmp ErrorEnv Do not pass any other code return ERROR_FAILURE Just a
125. program windows opens a window with a black background by default and initializes the standard input and standard output of the program before it starts If the program is marked as a windows program nothing is done and you can t use the text output or input library functions For historical reasons this window is called sometimes a DOS window even if there is no MSDOS since more than a decade The programs that run in this console window are 32 bit programs and they can open a window if they wish They can use all of the graphical features of windows The only problem is that an ugly black window will be always visible even if you open a new window You can change the type of program Icc win will generate by checking the corresponding boxes in the Linker tab of the configuration wizard accessible from the main menu with Project then Configuration Under other operating systems the situation is pretty much the same Linux offers a console and even the Macintosh has one too In many situations typing a simple command sequence is much faster than clicking dozens of menus options till you get where you want to go Besides an additional advantage is that console programs are easier to automate and make them part of bigger applications as independent components that receive command line arguments and pro duce their output without any human intervention 1 3 4 An overview of the compilation process When you press F9
126. rcpy function how ever expects a large enough destination buffer and a well formed source string If one of those requirements is not met a catastrophe happens strcpy will start destroying memory without any restriction Always check for those two conditions before using it This is easier said than done though Consider this code void func char p char buf 10 1 memset buf 0 sizeof buf limit string to 10 chars sprintf buf 10s p printf Hello s n buf Where is the error here We see that the destination buffer is cleaned with memset setting it to all zeroes We see that the size of the destination buffer is 10 1 i e the programmer takes into account the terminat ing zero of the destination string We see too that the sprintf format string indicates a field of 10 positions Since the eleventh position is already set to zero with memset the destination buffer should be always a correct string of at most 10 characters finished with zero Well let s test our assumptions We make a test program like this include lt stdio h gt include lt string h gt int main void char buf 30 214 C programming with Icc win32 int i memset buf 0 sizeof buf for i 0 i lt 14 i buf i a printf 3d i func buf return 0 t lcc mc45 test gt tbhuf 0 Hello a 1 Hello aa tbuf exe has encountered a problem and needs to close 2 Hello aaa We are
127. refers to the way the caller and the called function agrees as to who is going to adjust the stack after the call Parameters are passed to functions by pushing them into the system stack Normally it is the caller that adjusts the stack after the call returns With the stdcall calling convention it is the called function that does this It is slightly more efficient and contributes to keeping the code size small 101 API means Application Programmer Interface i e entry points into the windows system for use by the programmers like you and me Introduction to windows programming 231 hinstPrev Again this is a mysterious HANDLE to a previous instance of the program Again an unused parameter that will always contain zero maintained there for compatibil ity reasons with older software IpCmdLine This one is important It is actually a pointer to a character string that contains the command line arguments passed to the program Note that to the contrary of main there isn t an array of character pointers but just a single character string containing all the com mand line nCmdShow This one contains an integer that tells you if the program was called with the instruction that should remain hidden or should appear normally or other instructions that you should use when creating your main window We will ignore it for now OK OK now that we know what those strange parameters are used or not used for we can see what t
128. some part of the declaration For instance struct SomeType We know now that SomeType is a struct but since the contents aren t specified we can t use directly that type The use of this is precisely to avoid using the type encapsulation Many times you want to publish some interface but you do not want people using the structure allo cating a structure or doing anything else but pass those structure to your functions In those situations an opaque type is a good thing to have 1 6 7 Qualified types All types we have seen up to now are unqualified To each unqualified type corresponds one or more qualified type that adds the keywords const restrict and volatile The const keyword means that the programmer specifies that the value of the object of this type will not change during its lifetime The value of the object is constant The restrict keyword applies to pointer types and it means that there is no alias for this object i e that the pointer is the only pointer to this object within this function or local scope For instance void f int restrict p int restrict q while q p q Copy ptt Increment qtt During the execution of this function the restrict keyword ensures that when the object pointed to by p is accessed this doesn t access also the object pointed by q This keyword enables the compiler to perform optimizations based on the fact that p and q point to different objects
129. sometimes infinite delays occur This problem is avoided if the child process flushes the IO buffers after each call to a C run time IO function Only the child pro cess can flush its C run time IO buffers A process can flush its C run time IO buffers by call ing the fflush function NOTE Windows 95 and Windows 98 require an extra step when you redirect the standard handles of certain child processes 2 22 16 How to modify the width of the list of a combo box The combo box in Windows is actually a combination of two or more controls that s why it s called a combo box To make the combo box list wider or narrower you need the handle of the list box control within the combo box This task is difficult because the list box is actually a child of the desk top window for CBS_DROPDOWN and CBS_DROPDOWNLIST styles If it were a child of the ComboBox control dropping down the list box would clip it to the parent and it wouldn t display A combo box receives WM_CTLCOLOR messages for its component controls when they need to be painted This allows the combo box to specify a color for these controls The HIWORD of the lParam in this message is the type of the control In case of the combo box Windows sends it a WM_CTLCOLOR message with the HIWORD set to CTLCOLOR_LISTBOX when the list box control needs to be painted The LOWORD of the lParam contains the handle of the list box control Once you obtain the handle to the list box control wind
130. supply a corresponding pointer to a suitable sized location 3 Leading blanks are ignored except for the c character directive 4 The f format means float to enter a double you should write 31 5 Scanf ignores new lines and just skips over them However if we put a n in the input format string we force the system to skip a new line 6 Calls to scanf can t be intermixed with calls to getchar to the contrary of calls to printf and putchar 7 When scanf fails it stops reading at the position where it finds the first input character that doesn t correspond to the expected sequence If you are expecting a number and the user makes a mistake and types 465x67 scanf will leave the input pointing to the x that must be removed by other means Because of this problem it is always better to read one line of input and then using sscanf in the line buffer rather than using scanf directly with user input 80 C programming with Icc win32 Here are some common errors to avoid int integer short shortint char buffer 80 char str buffer providing the variable instead of a pointer to it sscanf d sscanf d integer amp integer wrong right providing a pointer to the wrong type or a wrong format to the right pointer sscanf Sd sscanf Shd amp shortint amp shortint wrong right providing a pointer to a string
131. system a message is sent to the window procedure of the concerned window For instance when you move the mouse over the surface of a window the system sends a message called WM_MOUSEMOVE to the win dows procedure informing it of the event There are quite a lot of messages and it would be horrible to be forced to reply to all of them in all the windows you create Fortunately you do not have to You just treat the messages that interest you and pass all the others to the default windows procedure 102 PLEASE never do this if you use the garbage collector 232 C Tutorial There are several types of default procedures for MDI windows we have MDIDefWin dowProc for normal windows we have DefWindowProc and for dialog boxes our case here we have the DefDlgProc procedure When creating a class of windows it is our job to tell windows which procedure should call when something for this window comes up so we use the class registration structure to inform it that we want that all messages be passed to the default dialog procedure and we do not want to bother to treat any of them We do this with wce lpfnWndProc DefDlgProc As we saw with the qsort example functions are first class objects in C and can be passed around easily We pass the address of the function to call to windows just by setting this field of our structure This is the most important thing conceptually that we do here Of course there is some other stuff
132. system in a convenient way In that system lines are separated by only ONE character the new line character When the MSDOS system was developed dozens of years later than UNIX people decided to separate the text lines with two characters the carriage return and the new line character This provoked many problems with software that expected only ONE char as line separator To avoid this problem the MSDOS people decided to provide a compatibility option for that case fopen would by default open text files in text mode i e would translate sequences of r n into n skipping the r Conclusion Instead of opening the file with fopen argv 1 r we use fopen argv 1 rb 1 e we force NO translation We recompile relink and we obtain H lcc examples gt countchars countchars c 493 H lcc examples gt dir countchars c 07 01 00 11 50p 493 countchars c 1 File s 493 bytes Yes 493 bytes instead of 492 before since we have added a b to the arguments of fopen Still we read the docs about file handling and we try to see if there are no hidden bugs in our program After a while an obvious fact appears we have opened a file but we never closed it i e we never break the connection between the program and the file it is reading We correct this and at the same time add some commentaries to make the purpose of the program clear Module H LCC EXAMPLE
133. the DuplicateHandle function and is responsible for cleanup when the object handle is closed 2 17 7 Inter Process Communications You can use the following primitives e Atoms An atom table is a system defined table that stores strings and corresponding identifiers An application places a string in an atom table and receives a 16 bit integer called an atom that can be used to access the string The system maintains a global atom Etc 319 table that can be used to send information to from one process to another instead of sending a string the processes send the atom id e Clipboard This is the natural way to do inter process communications under windows Copy and Paste e Mailslots A mailslot is a pseudofile it resides in memory and you use standard Win32 file functions to access it Unlike disk files however mailslots are temporary When all handles to a mailslot are closed the mailslot and all the data it contains are deleted A mailslot server is a process that creates and owns a mailslot A mailslot client is a process that writes a message to a mailslot Any process that has the name of a mailslot can put a message there Mailslots can broadcast messages within a domain If several processes in a domain each create a mailslot using the same name the participating processes receive every message that is addressed to that mailslot and sent to the domain Because one process can control both a server mailslot handle and the c
134. the calling program that message should disappear 244 C Tutorial The debugger tab is in the upper left corner When we select it we arrive at the following tab Configuration of Wedit these are the command line arguments h lcc examples dialogslcc h lcc examples dialog lec dialog exe E Note the first line Command line arguments to pass to program There we write the string that we want shown in the dialog box When now we press Ctrl F5 we see our dialog box like this these are the command line arguments Nice we can pass our dialog box a prompt string This makes our dialog box more useful as a general input routine Remember that the objective of this series of sections was to introduce you a general routine to input a character string from the user We are getting nearer Still there is one more problem that we haven t solved yet We have a buffer of a limited length i e 1024 characters We would like to limit the text that the user can enter in the dialog box so that we avoid overflowing our buffer We can do this with the message EM_SETLIMITTEXT We have to send this message to the control when we start the dialog box so that the limit will be effective before the user has an occasion of overflowing it We add then SendDlgItemMessage hDlg IDENTRYFIELD EM_SETLIMITTEXT 512 0 Libraries 245 2 3 Libraries What we would like is a way of using this dialog box in
135. the compiler will generate a warning when this happens 1 3 14 Careful with integer wraparound Consider this code bool func size t cbSize if cbSize lt 1024 we never deal with a string trailing null char buf malloc cbSize 1 memset buf 0 cbSize 1 do stuff free buf return true else return false Everything looks normal and perfect in the best of all worlds here We test if the size if smaller than a specified limit and we then allocate the new string But what happens if cbSize is zero Our call to malloc will ask for 0 1 bytes and using 32 bit arithmetic we will get an integer wrap around to OxfffffffFf or 1 We are asking then for a string of 4GB The program has died in the spot 96 I got this example from the excellent column of Michael Horward in the msdn security column Pitfalls of the C language 221 1 3 15 Problems with integer casting In general the compiler tries to preserve the value but casting from signed to unsigned types can produce unexpected results Look for instance at this sequence char c 0x80 128 now we cast it to short short s short c now s Oxff 80 still 128 unsigned short us unsigned short s us 0xff 80 which is 65408 In general you should not try to mix signed unsigned types in casts Casts can occur automatically as a result of the operations performed The operators addi tion bitwise negation
136. the screen a print preview If a screen font is available that exactly matches or at least very closely corresponds to the chosen printer font then the process is very straightforward and consists of seven steps 354 C Tutorial e Retrieve a Device Context DC or an Information Context IC for the printer e Call EnumFontFamilies to obtain a LOGFONT structure for the selected printer font The nFontType parameter to the EnumFontFamilies callback function specifies if a given font is a device font e Geta DC for the screen e Convert the lfHeight and lfWidth members of the LOGFONT structure from printer resolution units to screen resolution units If a mapping mode other than MM_TEXT is used round off error may occur e Call CreateFontIndirect with the LOGFONT structure e Call SelectObject GDI will select the appropriate screen font to match the printer font e Release the printer device context or information context and the screen device context If a screen font that corresponds to the selected printer font is not available the process is more difficult It is possible to modify the character placement on the screen to match the printer font to show justification line breaks and page layout However visual similarity between the printer fonts and screen fonts depends on a number of factors including the num ber and variety of screen fonts available the selected printer font and how the printer driver describes the
137. the size of the dialog boxes but they will not switch HIWORD wParam Handle the messages from the controls here exactly as you would in a dialog box break return 0 look very good if they were designed with different sizes When you have designed all dialog boxes and written all dialog box procedures you have all data necessary to call the PropertySheet API This API takes a complicated set of parameters in a custom structure One way to fill this structures is the following define NUMBEROFPAGES 16 static void DoPropertySheet HWND hwndOwner PROPSHEETPAGE psp NUMBEROFPAGES PROPSHEETHEADER psh int i memset psp 0 sizeof psp First we fill the PROPSHEETPAGE array with some items that will be common to all pages This is not necessary and maybe you will find it useful to fill individually this settings for i 0 i lt NUMBEROFPAGES i psp i dwSize sizeof PROPSHEETPAGE psp i dwFlags PSP_USETITLE PSP_DEFAULT psp i hInstance hInst Now we starting filling each page with the unique information it needs We fill the resource ID the callback procedure and the title i 0 psp i pszTemplate MAKEINTRESOURCE IDD_GENERALSETTINGS psp i pfnDlgProc EditInfo psp i pszTitle General itt Repeat for all pages psp i pszTemplate MAKEINTRESOURCE IDD_COMPILER psp i pfnDlgProc
138. the user s choices and ensures that the user selects a valid key combi nation Not supported in the resource editor IP address control Allows to input an IP address Not currently supported in the resource editor Month calendar Allows the user to choose a month or a calendar date The notifica tions use the prefix MCN_XXX Pager control A pager control is a window container that is used with a window that does not have enough display area to show all of its content The pager control allows the user to scroll to the area of the window that is not currently in view Not supported in the editor Progress bar A progress bar is a window that an application can use to indicate the progress of a lengthy operation It consists of a rectangle that is grad ually filled with the system highlight color as an operation pro gresses This control sends no notifications but receives messages that use the PBM_XXX prefix Window controls 271 Control Notifications Tab controls A tab control is analogous to the dividers in a notebook or the labels in a file cabinet By using a tab control an application can define multiple pages for the same area of a window or dialog box Each page consists of a certain type of information or a group of controls that the application displays when the user selects the corresponding tab The notifications specific to this control use the TCN_XXX pre fix Trackbar control A tr
139. this case the programmer decides that the number of pages will never exceed 31 so it can be safely stored in this small amount of memory We access the data stored in a structure with the following notation lt structure name gt field name or lt structure name gt field name We use the second notation when we have a pointer to a structure not the structure itself When we have the structure itself or a reference variable we use the point Here are some examples of this notation void fn void coordinate c coordinate pc coordinate amp rc c c x 67 Assigns the field x c y 78 Assigns the field y pe amp c We make pc point toc pc gt x 67 We change the field x to 67 pe gt y 33 We change the field y to 33 re x 88 References use the point notation Structures can contain other structures or types After we have defined the structure coordinate above we can use that structure within the definition of a new one struct DataPoint struct coordinate coords int Data This structure contains a coordinate structure To access the x field of our coordinate in a DataPoint structure we would write struct DataPoint dp dp coords x 78 Structures can be contained in arrays Here we declare an array of 25 coordinates struct coordinate coordArray 25 To access the x coordinate from the 4 member of the array we would write coordArray 3 x 89
140. this case the style indicates the appearance DS_MODALFRAMB that this window is visible has a caption and a system menu 3 The CAPTION statement indicates just what character string will be shown in the caption 4 In a similar way the FONT statement tells the system to use Helv 5 The following statements enumerate the controls of the dialog box and their descriptions are enclosed in a BEGIN END block We have two of them a push button that is the default push button and a normal pushbutton 6 the Cancel button Both of them have a certain text associated with them a set of coords as all controls and an ID that in the case of the OK button is the predefined symbol IDOK with the numerical value of 1 and in the case of the Cancel button IDCANCEL numerical value 2 To convert this set of instruction in this language into a binary resource file that windows can interpret we use a compiler called a resource compiler Microsoft s one is called rc Borland s one is called brc and Icc win s one is called Irc All of them take this resource language with some minor extensions depending on the compiler and produce a binary resource file for the run time interpreter of windows The resource compiler of Icc win is explained in detail in the technical documentation and we will not repeat that stuff again here For our purposes it is enough to know that it is compatible with the other ones The binary resour
141. this line Memory management and memory layout 141 1 29 Memory management and memory layout We have until now ignored the problem of memory management We ask for more memory from the system but we never release it we are permanently leaking memory This isn t a big problem in these small example applications but we would surely run into trouble in bigger undertakings Memory is organized in a program in different areas 1 The initial data area of the program Here are stored compile time constants like the character strings we use the tables we input as immediate program data the space we allocate in fixed size arrays and other items This area is further divided into initialized data and uninitialized data that the program loader sets to zero before the program starts When you write a declaration like int data 78 the data variable will be stored in the initialized data area When you just write at the global level int data the variable will be stored in the uninitialized data area and its value will be zero at program start 2 The stack Here is stored the procedure frame i e the arguments and local variables of each function This storage is dynamic it grows and shrinks when procedures are called and they return At any moment we have a stack pointer stored in a machine register that contains the machine address of the topmost position of the stack 3 The heap Here is the space that we obtain with malloc or equiv
142. to a function call with the big difference that the arguments of the function call is evaluated once but in the macro can be evaluated several times For instance we have the macro square define square a a a If we use it like this b square a After expansion this will be converted into b a a and the variable a will be incremented twice 174 C programming with Icc win32 1 35 Using function pointers A very common programming problem is to recursively explore a certain part of the file sys tem to find files that have a certain name for instance you want to know all the files with the c extension in a directory and in all subdirectories To build such a utility you can do 1 Build a list or table containing each file found and return those results to the user 2 For each file that is found you call a user provided function that will receive the name of the file found The user decides what does he she want to do with the file Note that solution 2 includes solution 1 since the user can write a function that builds the list or table in the format he wants instead of in a predefined format Besides there are many options as to what information should be provided to the user Is he interested in the size of the file Or in the date Who knows You can t know it in advance and the most flexible solution is the best We can implement this by using a function pointer that will be called by the
143. to have a right mouse menu or a dialog box with much more information etc This is just a blueprint to get you started however The whole code for this program is in the appendix 4 282 C Tutorial 2 11 Numerical calculations in C Well we have a beautiful window with nothing in it Blank It would look better if we would draw something in it isn t it By the way this is an introduction to C not to windows What can we draw Let s draw a galaxy In his wonderful book Computers Pattern Chaos and Beauty Clifford A Pickover writes We will approximate a galaxy viewed from above with logarithmic spirals They are eas ily programmable in a computer representing their stars with just dots One arm is 180 degrees out of phase with the other To obtain a picture of a galactic distribution of dots simply plot dots at r according to r el tan r el a tan where rl and r2 correspond to the intertwined spiral arms The curvature of the galactic arms is controlled by which should be about 0 2 radians for realistic results In addi tion O0 lt lt 1000 radians For greater realism a small amount of random jitter may be added to the final points He is kind enough to provide us with a formal description of the program in some computer language similar to BASIC Here it is Algorithm How to produce a galaxy Notes The program produces a double logarithmic spiral The purpose of the random number
144. to its allocator function is done 4 If you have only one reference to a block the block will be retained If you have stored somewhere a pointer to a block no longer needed it can be very difficult indeed to find it 5 The garbage collector of lcc win is a conservative one i e if something in the stack looks like a pointer it will be assumed that this is a pointer fail safe and the memory block referenced will be retained This means that if by chance you are working with numeric data that contains numbers that can be interpreted as valid memory addresses more memory will be retained than strictly necessary The collector provides special APIs for allocating tables that contain no pointers and whose contents will be ignored by the collector Use them to avoid this problems 1 30 7 Mixed strategies Obviously you can use any combination of this methods in your programs But some methods do not mix well For instance combining malloc free with automatic garbage collection exposes you to more errors than using only one strategy If you pass to free a pointer allocated with GC_malloc chaos will reign in your memory areas To the contrary the stack allocation strategy can be combined very well with all other strategies since it is specially adapted to the allocation of small buffers that make for many of the calls to the allocator functions 1 30 8 A debugging implementation of malloc Instead of using directly malloc free here are two impleme
145. to run this program Suppose that we have entered the text of the program in the file args c We do the following h lec projects args gt lec args c h lec projects args gt lcclnk args obj We first compile the text file to an object file using the lcc compiler Then we link the result ing object file to obtain an executable using the linker Icclnk Now we can invoke the program just by typing its name h lec projects args gt args Argument 0 args We have given no arguments so only argv 0 is displayed the name of the program in this case args Note that if we write h lcc projects args gt args exe Argument 0 args exe We can even write h lcc projects args gt h lcec projects args exe Argument 0 h lcc projects args exe But that wasn t the objective of the program More interesting is to write h lcc projects args gt args foo bar zzz Argument 0 args Argument 1 foo Argument 2 bar Argument 3 zzz The program receives 3 arguments so argc will have a value of 4 Since our variable count will run from 0 to argc 1 we will display 4 arguments the zeroth the first the second etc 1 4 2 1 Implementation details The arguments are retrieved from the operating system by the code that calls main Some operating systems provide a specific interface for doing this others will pass the arguments to the startup Since C can run in circuit boards where there is no operating system a
146. understand the code above doesn t test the result of setting the signal han dler A more robust version looks like this include lt signal h gt include lt stdio h gt include lt stdlib h gt For exit snip for brevity int main void char p NULL void oldhandler int oldhandler signal SIGSEGV traphandler if oldhandler SIG_ERR printf Impossible to establish a signal handler n exit EXIT_FAILURE p 0 signal SIGSEGV oldhandler return 0 This code tests if the return value of the signal call is OK Besides before the function exists the old handler will be restored The software signals that lcc win supports are described in the standard header file lt sig nal h gt They include SIGSEGV for illegal addresses SIGFPE floating point exceptions and others In general the signal mechanism is barely supported by the operating system under Windows 1 36 6 2 Using the signal mechanism What can we do within our rescue function Not much We can t call any library functions since they could call signal too and they are not reentrant Besides when we return from the signal handling function we will end up crashing anyway since the signal mechanism will continue at the point where the program failed Since signal disables the specific signal that was raised the second time we trap the program will crash 190 C programming with Icc win32 A way out of this d
147. variables to the parent environment Under Windows there is no export directive as in Unix systems To propagate the value of an environment variable to the rest of the system use the following registry key HKEY_CURRENT_USER Environment You can modify system environment variables by editing the following registry key HKEY_LOCAL_MACHINE SYSTEM CurrentControlSet Control Session Manager Environment Note that any environment variable that needs to be expanded for example when you use SYSTEM must be stored in the registry as a REG_EXPAND_SZ registry value Any val ues of type REG_SZ will not be expanded when read from the registry The problem with this method however is that changes will be effective only after the next logoff probably not exactly what you want To effect these changes without having to log off broadcast a WM_SETTINGCHANGE mes sage to all windows in the system so that any applicable applications such as Program Man ager Task Manager Control Panel etc can perform an update SendMessageTimeout HWND_BROADCAST WM_SETTINGCHANGE 0 LPARAM Environment SMTO_ABORTIFHUNG 5000 amp dwReturnValue In theory this will work but there is a problem with Windows 95 Under that system there is no other way to set those variables than rebooting the system 2 21 13 Restarting the shell under program control In many cases it can be necessar
148. wParam LPARAM lParam HDC HDC COLORREF oldcolor switch msg case WM_INITDIALOG LoadListboxBitmaps hwnd other initializations can follow case WM_DRAWITEM DrawListboxLine hwnd LPDRAWITEMSTRUCT 1Param return 1 We processed this message case WM_NCDESTROY DestroyListboxBitmaps hwnd other cleanup tasks can go here Our procedure to draw each line of the dialog box can look like this long DrawListboxLine HWND hwndDlg LPDRAWITEMSTRUCT lpdis HBITMAP hbmpPicture hbmpOld int y state HDC hdcMem TEXTMETRIC tm RECT rcBitmap COLORREF oldcolor char tchBuffer 200 If there are no list box items skip this message if lpdis gt itemID 1 return 0 304 C Tutorial switch lpdis gt itemAction case ODA_SELECT case ODA_DRAWENTIRE Windows DOES NOT erase the background of owner draw list boxes Erase the background to start with a coherent state FillRect lpdis gt hDC amp lpdis gt rcItem GetStockObject WHITE_BRUSH We get the handle of the bitmap to draw from the item data slot in each list box line The initialization procedure sets this hbmpPicture HBITMAP SendMessage lpdis gt hwndItem LB_GETITEMDATA lpdis gt itemID LPARAM 0 We select the image in a memory DC then we select it This is a standard technique for copying a bitmap into the screen hdcMem CreateCompatib
149. will we use the DLL DLLs can be loaded into the program s address space with the API LoadLibrary This API will do what the program loader does when loading a program that contains a reference to a DLL If the load succeeds the API will return us a handle to the library if not it will return us an INVALID_HANDLE as defined in windows h After loading the DLL we can get the address of any exported function within that DLL just by calling another windows API GetProcAddress This API receives a valid DLL handle and a character string containing the name of the function to find and will return an address that we can store in a function pointer Let s do this include lt windows h gt 1 include lt stdio h gt 2 int APIENTRY pfnGetString char char int 3 int main int argc char argv char buffer 1024 HANDLE dlliHandle LoadLibrary 4 h lcc examples dialog lcc dialog dll if dllHandle INVALID _HANDLE_ VALUE 5 fprintf stderr Impossible to load the dll n exit 0 pfnGetString int APIENTRY char char int GetProcAddress dllHandle _GetString 12 6 if pfnGetString NULL fprintf stderr Impossible to find the procedure GetString n exit 1 if pfnGetString Enter a string buffer sizeof buffer printf String is s n buffer else printf User cancelled n return 0 We go step by step
150. with Icc win but the book is more complete and up to date The Standard C Library P J Plauger This book shows you an implementation with the source code of the standard C library done by somebody that is in the standards committee and knows what he is speaking about One of the best ways of learning C is to read C This will give you a lot of examples of well written C and show you how a big project can be structured The C Standard John Wiley and Sons This is the reference book for the language It contains the complete C standard and the ratio nale explaining some fine points of the standard Buffer Overflows Attacks and Defenses for the Vulnerability of the Decade Crispin Cowan Perry Wagle Calton Pu Steve Beattie and Jonathan Walpole Department of Computer Science and Engineering Oregon Graduate Institute of Science amp Technology URL http downloads securityfocus com library discex00 pdf Introduction to windows programming 227 Windows Programming 2 1 Introduction to windows programming OK up to now we have built a small program that receives all its input from a file This is more or less easy but a normal program will need some input from the user input that can t be passed through command line arguments or files At this point many introductory texts start explaining scanf and other standard functions to get input from a command line interface This can be OK but I think a normal program under wi
151. would need to protect asctime from buffer overflows in the worst case This is very easy to calculate We know that in all cases sd can t output more characters than the maximum numbers of characters an integer can hold This is INT_MAX and taking into account the possible negative sign we know that Number of digits N 1 ceil log10 double INT_MAX For a 32 bit system this is 11 for a 64 bit system this is 21 In the asctime specification there are 5 d format specifications meaning that we have as the size for the buffer the expression 26 5 N bytes In a 32 bit system this is 26 55 81 This is a worst case oversized buffer since we have already counted some of those digits in the original calculation where we have allowed for 3 2 2 2 4 13 characters for the digits A tighter calculation can be done like this Number of characters besides specifications d or s in the string 6 Number of d specs 5 Total 6 5 11 61 terminating zero 62 The correct buffer size for a 32 bit system is 62 1 28 1 2 Buffer overflows are not inevitable As we have seen above a bit of reflection and some easy calculations allows us to determine how much we need exactly Most buffer overflows come from people not doing those calcula tions because C is full of buffer overflows anyway attitude What is absolutely incredible however is to find a buffer overflow in the text of the last official C standard An international s
152. would provide an API for each one the windows API would not fit in a computer no matter what The solution provided by the system is a general interface that gives you enough elements to be able to do whatever you want to do You can 1 customize the appearance of a control by making some of its parts owner draw i e drawed by yourself 2 Process some special windows messages that allow you to change the font the background color and other characteristics by modifying the settings of a passed device context HDC In both cases the interface is quite simple Windows sends a message to the procedure of the parent window of the control to ask it to draw a specific part of the control Some or all of the control behavior is retained but the appearance can be changed as you like 2 14 1 Processing the WM_CTLCOLORXXX message We can start with a simple example that draws a listbox in a special way Let s use the second method first since it is easier Suppose we want to display the text in a listbox in red color In the dialog procedure which owns the list box or in the windows procedure if it is a list box created independently you receive the WM_CTLCOLORLISTBOX message In the wparam parameter you receive an HDC that you can customize using SetTextColor to draw the text with the color you wish To inform windows that you have processed this message you should return a handle to a brush that will be used to paint the backgrou
153. zero byte If for whatever reason the passed string does not have a zero byte this program will go on scanning memory until a zero byte is found by coincidence or it will crash when attempting to reference inexistent memory 1 17 3 ispowerOfTwo Given a positive number find out if it is a power of two Algorithm A power of two has only one bit set in binary representation We count the bits If we find a bit count different than one we return 0 if there is only one bit set we return 1 Implementation We test the rightmost bit and we use the shift operator to shift the bits right shifting out the bit that we have tested For instance if we have the bit pattern 1 0 0 1 shifting it right by one gives O 1 0 0 the rightmost bit has disappeared and at the left we have a new bit shifted in that is always zero int ispowerOfTwo unsigned int n unsigned int bitcount 0 while n 0 if n amp 1 bitcount t t n n gt gt 1 if bitcount 1 return 1 return 0 51 The expression p 0 could have been written in the form while p using the implicit test for a non zero result in any logical expression Any expression will be considered true if its value is anything but zero It is better however to make comparisons explicit Simple programs 91 Our condition here is that n must be different than zero i e there must be still some bits to count to go on We test the rightmost bi
154. 0 long double 7fff fffffffTf ffffffff 7fff 80000000 00000000 ffff 80000000 00000000 We have actually two types of NANs quiet NANSs and signalling NANS A Quiet NaN when used as an operand in any floating point operation quietly that is without causing any trap or exception produces another quiet NaN as the result which in turn propa gates A Quiet NaN has a 1 set in the most significant bit position in the mantissa field A Signaling NaN has no business inside an FPU Its very presence means a serious error Sig naling NaNs are intended to set off an alarm the moment they are fetched as an operand of a floating point instruction FPUs are designed to raise a trap signal when they touch a bit pat tern like that Quiet NaNs are produced when you do things like try to divide by zero or you pass incorrect arguments to a standard FPU function for instance taking the square root of 1 Modern FPUs have the ability to either produce a quiet NaN or raise a signal of some sort when they encounter such operands on such instructions They can be initialized to do either of the two options in case the code runs into these situations We will see this in more details in the exceptions section further down 1 37 2 What can we do with those numbers then Let s do some experiments with this formats 1 37 2 1 Range OK We have seen how floating point numbers are stored in memory To give us an idea of the range a
155. 0158682 I2 0 0580389 12 0 0129767 I22 0 124796 I3 0 0431387 13 0 0120398 T23 0 5805 I4 0 0343063 14 0 0112295 I24 2 94417 I5 0 0284684 15 0 0105192 I25 14 6808 I6 0 0243249 16 0 00990385 I26 73 4427 Ty 0 0212326 17 0 00930427 I27 367 176 I8 0 0188369 18 0 00903421 128 1835 92 19 0 0169265 19 0 00746051 I10 0 0153676 120 0 0126975 We see that now we can go up to the 19th iteration with apparently good results We see too that the increased precision has only masked a fundamental flaw of the algorithm itself The manner the calculation is done produces a five fold increase in the error term at each iteration This is an example of a numerically unstable algorithm EXERCISE 2 Explain the following output include lt stdio h gt int main void float a 0 7 if 0 7 gt a else printf OK n Output 222222 1 0 1 Complex numbers The C99 edition of the standard introduced complex numbers into the language Complex numbers have a real and an imaginary part According to which concrete number representa tion is used to store those parts they can be 1 float Complex 2 double _Complex 3 long double _Complex 4 Lec win introduces qfloat Complex too In Icc win all complex types except qfloat Complex will be subsumed into the long double complex type This implementation can be changed later but in any case it is better that you are aware of t
156. 4 bits need a much more complicated schema since arguments are not passed in the stack but in predetermined registers This forces the compiler to save all possible registers in a stack area and retrieve the arguments from there The issue is further complicated because some arguments are passed in some register sets integer arguments for instance are passed in a different set as floating point arguments and the compiler should keep pointers to different stack areas 1 13 7 Assignment An assignment expression has two parts the left hand side of the equal s sign that must be a value that can be assigned to and the right hand side that can be any expression other than void int a 789 a is assigned 789 array 345 array 123 897 An element of an array is assigned Struct field sqrt b 9 0 A field of a structure is assigned p gt field sqrt bt 9 0 A field of a structure is assigned through a pointer Within an assignment there is the concept of L value i e any assignable object You can t for instance write 5 8 The constant 5 can t be assigned to It is not an L value the L comes from the left hand side of the equals sign of course In the same vein we speak of LHS and RHS as abbreviations for left hand side and right hand side of the equals sign in an assignment 56 C programming with Icc win32 The rules for type compatibility in assignment are also used when examining
157. 5 data printf Unable to send n goto end if Receive amp session 5 buf printf Unable to receive n goto end buf session BytesReceived 0 printf Received d bytes 5s n session BytesReceived buf end CloseSession amp session Simple isn t it A server looks like this include lt stdio h gt include netutils h int main int argc char argv Session session char buf 8192 memset amp session 0 sizeof session session port 25876 session Host 127 0 0 1 if ServerConnect amp session return 0 printf Connected n memset buf 0 sizeof buf if Receive amp session sizeof buf 1 buf return 0 printf received request n printf data is s n buf if Send amp session 5 data return 0 CloseSession amp session Basically those procedures implement all the steps described above for client and server sides They are the building blocks for implementing the FTP or HTTP protocols we saw above To use this functions include netutils lib in the linker command line and include netutils h to get the prototypes and structure declarations 404 C Tutorial
158. 511209926324736e 025 26 4 03291573376593 6e 026 27 1 088886923454107e 028 28 3 0488839051318128e 029 29 8 8417606614675607e 030 30 2 6525290930453747e 032 31 8 2228384475874814e 033 32 2 631308303227994e 035 33 8 6833178760213554e 036 34 2 952328838437621e 038 Max factorial is 34 This measures the range of numbers stored in the float format i e the capacity of this format to store big numbers We modify slightly our program by replacing the float numbers by double numbers and we obtain this 1 1 2 2 3 6 4 24 Numerical programming 197 168 2 5260757449731988e 302 169 4 2690680090047056e 304 170 7 257415615308004e 306 Max factorial is 170 The range of double precision floats is much greater We can go up to 170 quite a big num ber Even greater as expected is the range of long doubles where we obtain 1751 3 674156538617319512e 4920 1752 6 437122255657543772e 4923 1753 1 128427531416767423e 4927 1754 1 979261890105010059e 4930 Max factorial is 1754 Changing the declarations of the numbers to qfloats and increasing the printing precision increases even more the range 3207 2 68603536247213602472539298328381221236937795484607e 9853 3208 8 61680144281061236731906069037446957728096447914618e 9856 3209 2 76513158299792550867268657554116728734946150135801e 9860 Max factorial is 3209 The range increases by more than 3 000 orders of magnitude 1
159. 5535 consists of eight 1s in binary notation since 65535 2 6 1 If the test fails this means that the least significant bit can t be in the lower 16 bits He increases the counter by 16 and shifts right the number to skip the 8 bits already known to contain zero If the test succeeds this means that there is at least a bit set in the lower 16 bits Nothing is done and the program continues to test the lower 16 bits He uses the same reasoning with the 16 bits in x that now contain either the high or the lower word of x 255 is 28 1 This is applied then recursively At each step we test 16 then 8 then 4 then 2 and at the end the last bit 95 This is based in a discussion of comp lang c 218 C programming with Icc win32 int main void int a b a 10 a gt 10 b 20 b 30 Error in this line printf d b This will provoke an error If we rewrite the above line like this a gt 10 b 20 b 30 the error disappears Why The explanation is that the first line is parsed as a gt 10 b 20 b 30 because of the established precedence of the operators The assignment operator is one of the weakest binding operators in C 1 e its precedence is very low The correct way to write the expression above is b a lt 10 20 10 1 3 7 Extra Semi colon in Macros The next code fragment illustrates a common error when using the preprocessor to define con stants define MAXVAL 10 note the semi
160. 601 te 79 Thope this happens to you too Time and Date functions 161 To convert from the ANSI C time format to the Windows time format you can use the follow Function Purpose CompareFileTime Compares two 64 bit file times DosDateTimeToFileT ime Converts MS DOS date and time values to a 64 bit file time FileTimeToDosDateTime Converts a 64 bit file time to MS DOS date and time values FileTimeToLocalFileTime Converts a file time based on the Coordinated Universal Time UTC to a local file time FileTimeToSystemTime Converts a 64 bit file time to system time format GetFileTime Retrieves the date and time that a file was created last accessed and last modified GetLocalTime Retrieves the current local date and time GetSystemTime Retrieves the current system date and time GetSystemT imeAdjustment Determines whether the system is applying periodic time adjustments to its time of day clock at each clock interrupt along with the value and period of any such adjustments GetSystemT imeAsFileTime Obtains the current system date and time The information is in Coordinated Universal Time UTC format GetTickCount Retrieves the number of milliseconds that have elapsed since the system was started It is limited to the resolution of the system timer GetTimeZonel nformation Retrieves the current time zone parameters These parameters control t
161. ADER_NAMF_BY_INDEX swzHeaders amp dwSize WINHTTP_NO_HEADER_INDEX 392 C Tutorial We got the headers Now we parse them to find the return code in them The standard HTTP specifies a response like HTTP 1 1 200 OK Date Fri 07 May 2004 09 08 14 GMT Server Microsoft IIS 6 0 P3P CP ALL IND DSP COR ADM CONo CUR CUSo IVAo IVDo PSA PSD TAI T OUR SAMo CNT COM INT NAV ONL PHY PRE PUR UNI X Powered By ASP NET Content Length 39601 Content Type text html Expires Fri 07 May 2004 09 08 14 GMT Cache control private zal ER O We are interested in the first line that contains the return code for the operation We just skip the HTTP 1 1 and get it memset szHeaders 0 dwSize wcstombs szHeaders swzHeaders dwSize char p szHeaders while p ptt while p ptt sscanf p d amp rc if re 404 reContext Status 404 goto cleanup The next thing to do is to open the output file If we can t open it there is no point in going further We close the session and return an error code rcContext OutputFile fopen outfile wb if rcContext OutputFile NULL WinHttpCloseHandle hSession return 2 Now we have everything We have an open file ready to receive the data a correct answer from the server that tells that the file exists so we have just to loop getting the data chunks unti
162. C compiler myself Note that we have taken the a and b elements of a plain int not the struct that contains them The operator works on any Ivalue in this early C and all the structure member names must be unique no other struct can have members named a and b We can and people did also write things like struct rkreg unsigned rkcsr rkdar rkwc read disk sector s 0777440 gt rkdar addr 0777440 gt rkwe bytecount 2 0777440 gt rkcsr RK_READ RK _GO Note that the gt operator works on any value not just pointers Since this early C did not look at the left hand side of the and gt operators it really did require different operators to achieve different effects These odd aspects of C were fixed even before the very first C book came out but as with the wrong precedence for the bitwise amp and l operators the historical bag gage went along for the ride 1 13 36 Indirection The operator is the contrary of the address of operator above It expects a pointer and returns the object the pointer is pointing to For instance if you have a pointer pint that points to an integer the operation pint will yield the integer value the pointer pint is pointing to The result of this operator is invalid if the pointer it is de referencing is not valid In some cases de referencing an invalid pointer will provoke the dreaded window This pr
163. C programming with Icc win32 GC_malloc sizeof struct DataPoint 67 This will allocate space for 67 structures of type DataPoint as defined above Note that we could have written GC_malloc 804 since we have struct DataPoint struct coordinate coords int Data We can add the sizes Two integers of 4 bytes for the coordinate member makes 8 bytes plus 4 bytes for the Data member makes 12 that multiplies 67 to make 804 bytes But this is very risky because of the alignment mentioned above Besides if you add a new member to the structure the sizeof specification will continue to work since the compiler will correctly recalculate it each time If you write the 804 however when you add a new member to the structure this number has to be recalculated again making one more thing that can go wrong in your program In general it is always better to use compiler calculated constants with sizeof instead of using hard wired numbers When designing a data type layout it is important to have padding issues in mind If we define a structure like this struct s char a int b char c it will use 12 bytes in most 32 bit compilers If we rearrange the members like this struct s char a char c int b it will use only 8 bytes of memory a reduction of 33 in size 1 20 3 Defining new types Structures are then a way of augmenting the type system by defining new types using already defi
164. CLOSE DestroyWindow hWnd break ID TI TextOu lstrlen SZ_INIT break ID_TI TextOu T case R_INIT t hDC E SZ_INIT case ER_LOAD t HDC rce rig SZ_LOAD lstrlen SZ_LOAD break ID TI TextOu F ER_DONE t hDC case EORELG SZ_CLOSE T lstrlen SZ_CLOS Gl T tOsright 200 L rc bottom 20 ht 200 rc bottom 20 ht 200 rc bottom 20 364 C Tutorial break ReleaseDC hWnd hDC break default return DefWindowProc hWnd message wParam lParam return 0 2 22 13 How do append text to an edit control Windows based applications often use edit controls to display text These applications some times need to append text to the end of an edit control instead of replacing the existing text There are two different ways to do this in Windows Use the EM_SETSEL and EM_REPLACESEL messages Use the EM_SETSEL message with the clipboard functions to append text to the edit control s buffer The EM_SETSEL message can be used to place a selected range of text in a Windows edit control If the starting and ending positions of the range are set to the same position no selec tion is made and a caret can be placed at that position To place a caret at the end of the text in a Windows edit control and set the focus to the edit control do the following HWND hEdit GetDlgItem hDlg ID_EDIT int ndx GetWi
165. CP IP subsystem for network programming e CommonControls doc This explains the new controls added to windows after 1995 Note that Wedit will detect if the documentation is installed and will allow you to see the doc umentation of any function just with pressing the F1 key This is a nice feature especially for beginners Install a full version if you aren t an expert A version without the documentation it is a pain since you have to go fishing for that information each time you want to call an API not a very exciting perspective But if you want to get serious about windows programming you should download the Micro soft Software Development Kit SDK from the msdn site and install it in your machine Wedit will automatically recognize the msdn library or the SDK if installed and will call them instead of using the win32 hlp file 2 25 Bibliography Here are some books about programming in Windows I recommend you to read them before you believe what I say about them 2 25 1 Books Programming Windows Charles Petzold Microsoft Press This is a very easy to read introduction to the windows API that covers in depth all aspects of windows programming You can download an electronic version of this book at the site of the author www cpetzold com Windows Network Programming Ralph Davis Addison Wesley 386 C Tutorial This is a very extensive introduction to this side of programming If you want an in depth cov era
166. E O OL This pseudo code appends text to the end of the edit control Note that the data in the clip board must be in CF_TEXT format 2 22 14 How do I determine the color settings Here is a small code snippet that will show the current screen color settings incl incl incl lude lt wi lude lt st lude lt st ndows h gt dio h gt dbool h gt int main void HDC hDC INE int Bits bool If nf swit case case case case case case prin Rele hDC GetDC HWND_DESKTOP BitsPerPixel GetDeviceCaps hDC BITSPIXEL Planes GetDeviceCaps hDC PLANES PerPixel Planes UsesPalettes bool GetDeviceCaps hDC RASTERCAPS amp RC_PALETTE UsesPalettes printf System uses palettes n ch BitsPerPixel 32 printf 32 bit true color break 24 printf 24 bit true color break 16 printf 16 bit high color break 8 printf 256 color mode break 4 printf 16 color mode break 1 printf Monochrome mode break t n aseDC HWND_DESKTOP hDC FAQ 365 2 22 15 How do I spawn a process with redirected stdin and stdout The CreateProcess API through the STARTUPINFO structure enables you to redirect the standard handles of a child console based process If the dwFlags member is set to STARTF_USESTDHANDLES then the following STARTUPINFO members specify the stan
167. E 3 An alternative version of the above program is include lt stdio h gt int main void volatile double oneplus 2 epsilon 1 while 1 epsilon 2 gt 1 epsilon 2 oneplus 1 epsilon epsilon oneplus 1 printf DBL_EPSILON is g n epsilon return 0 Explain why this program prints DBL_EPSILON is 0 in Icc win 1 0 0 1 Rounding When in C you convert a floating point number into an integer the result is calculated using rounding towards zero To see this in action look at this simple program include lt stdio h gt void fn double a printf int g d int g d n a int a a int a int main void for double d 1 2 d lt 2 0 d 0 3 fn d return 0 This leads to the following output note the lack of precision 0 3 can t be exactly represented in binary int 1 5 1 int 1 5 1 int 1 2 1 int 1 2 1 int 0 9 0 int 0 9 0 int 0 6 0 int 0 6 0 int 0 3 0 int 0 3 0 int 1 11022e 016 0 int 1 11022e 016 0 int 0 3 0 int 0 3 0 int 0 6 0 int 0 6 0 int 0 9 0 int 0 9 0 int 1 2 1 int 1 2 1 int 1 5 1 int 1 5 1 Using the floating point environment 203 int 1 8 1 int 1 8 1 To round away from zero you can use define Round x x gt 0 long x 0 5 long x 0 5 This will give nonsense results if there is an over
168. ENTRYFIELD return 1 We add this call in the procedure InitializeApp We test and it doesn t work We still have to click in the edit field to start using it Why Because when we read the documentation of the WM_INITDIALOG message it says WM_INITDIALOG hwndFocus HWND wParam handle of control to receive focus lInitParam lParam initialization parameter Parameters hwndFocus Value of wParam Identifies the control to receive the default keyboard focus Windows assigns the default keyboard focus only if the dialog box procedure returns TRUE Well that is it We have to return FALSE and our SetFocus API will set the focus to the con trol we want We change that and it works Another bug is gone 108 Note that the SetFocus API wants a window handle To get to the window handle of a control in the dialog box we use its ID that we took care of defining in the dialog editor Basically we 106 You put the cursor under the WM_INITDIALOG identifier and press F1 107 This example shows you how to get rid of those problems and the kind of problems you will encounter when programming under Windows The only solution in most cases is a detailed reading of the documentation Fortunately Windows comes with a clear documentation that solves most problems 108 All the notifications messages from edit fields begin with the EN_ prefix meaning Edit field Notification Introduction to windows programming
169. ETX pt y GetDeviceCaps hPrnDC PHYSICALOFFSETY Determine the number of pixels required to yield the desired margin x and y offsets by calling GetDeviceCaps using the LOGPIXELSX and LOGPIXELSY flags Figure out how much you need to offset output to produce the left and top margins for the output in the printer Note the use of the max macro It is possible that you are asking for margins that are not possible on this printer For example the HP LaserJet has a 0 25 unprintable area so we cannot get margins of 0 1 xOffset max 0 GetDeviceCaps hPrnDC LOGPIXELSX nIinchesWeWant pt x yOffset max 0 GetDeviceCaps hPrnDC LOGPIXELSY nIinchesWeWant pt y When doing all the output you can either offset it by the above values or call SetViewportOrg to set the point 0 0 at the margin offset you calculated SetViewportOrg hPrnDC xOffset yOffset all other output here e Calculate the bottom and right margins Obtain the total size of the physical page including printable and unprintable areas calling GetDeviceCaps with the PHYSICALWIDTH and PHYSICALHEIGHT indices in Windows NT e Determine the number of pixels required to yield the desired right and bottom margins by calling GetDeviceCaps using the LOGPIXELSX and LOGPIXELSY flags e Calculate the size of the printable area with GetDeviceCaps using the HORZRES and VERTRES flags The following code fragment
170. FOF_NOCONFIRMATION sh wFunc FO_DELETE sh pFrom buf sh pTo NULL if bDelete sh fFlags amp FOF_ALLOWUNDO else sh fFlags FOF_ALLOWUNDO return SHFileOperation amp sh ifdef TEST Test program include lt gc h gt tinclude lt sys stat h gt H OSE the command line typedef struct tagFileList struct tagFileList Next char Name FILELIST pre declare functions usage void void help void char GetCurrentDir void char MakeAbsolute char relname confirm LPCTSTR pFileName LPCTSTR GetErrorMsg int err BOOL global command line switches send to Recycle Bin for GC_malloc For stat This list structure holds the names of the files given in BOOL BOOL bPrompt FALSE bQuiet FALSE BOOL bDisplayOnly FALSE prompt at each file don t display messages display results only don t erase BOOL bZap FALSE test if file exists delete don t recycle int fileexists LPCTSTR pFilename struct stat st return stat pFilename amp st 0 Adds to the list of file a new name Allocates memory with the garbage collector FILELIST AddToList FILELIST start char name FILELIST newlist int main int argc newlist GC_malloc newlist gt Nam FAQ 375 sizeof FILELIST GC_malloc strlen name 1
171. FS for magneto optical storage media mainly DVD ROM UDF is included in the DVD specification and is more flexible than CDFS 2 17 5 Graphics GDI is the lowest level the basic machinery for drawing It provides you e Bitmap support e Brush support for painting polygons e Clipping that allows you to draw within the context of your window without worrying that you could overwrite something in your neighbor s window Filled shapes polygons ellipses pie rectangle lines and curves e Color management palettes etc e Coordinate spaces and transforms e Text primitives for text layout fonts captions and others e Printing But higher levels in such a vast field like graphics are surely possible Lcc win offers the stan dard jpeg library of Intel Corp to read write and display jpeg files Under windows you can do OpenGIl an imaging system by Silicon Graphics or use DirectX developed by Microsoft 2 17 6 Handles and Objects An object is implemented by the system with a standard header and object specific attributes Since all objects have the same structure there is a single object manager that maintains all objects Object attributes include the name so that objects can be referenced by name secu rity descriptors to rule access to the information stored in those objects and others for instance properties that allow the system to enforce quotas The system object manager allows mapping of handles from one process to another
172. GetFile else printf Remote file s gt local file s szFilel szFile2 if InternetCloseHandl hConnect ErrorOut InternetCloseHandle else ErrorOut InternetConnect InternetCloseHandle hOpen return 0 This program is about 400 bytes of code and 200 bytes of data for character strings When linked it is only 4K long The whole hard part of networking is hidden behind the windows interface provided by the wininet lib library and the wininet h header file Basically to get a file from a remote machine using the FTP File Transfer Protocol you need to open a connection to the remote server send it the path of the file to retrieve and that is it The rest is some logic for opening and initializing the wininet library and taking care of possi ble errors Please be aware that all this supposes that you have a working TCP IP network connection and that the lower layers of the network are working Besides note that the paths given here may change etc etc Network programming is covered in more detail in chapter 3 2 18 4 Opening a web site or an HTML file using the default browser The ShellExecute API will call the registered default browser when invoked like this 1 Opening an HTML file in the local hard drive ShellExecute Handle open d website index htm NULL NULL SW_SHOWDEFAULT 2 Opening a web site
173. If that is the case the compiler emits a record for the linker telling it that this object is defined elsewhere 27 Note that when you do not provide for a declaration and use this feature definition is a declaration you can only use the defined object after it is defined A declaration placed at the beginning of the program module or in a header file frees you from this constraint You can start using the identifier immediately even if its definition comes much later or even in another module 22 C programming with Icc win32 int a 1024 1024 16 but the values you assign must be compile time constants i e values that the compiler can fig ure out when doing its job Pointers are declared using an asterisk int a This means that a will contain the machine address of some unspecified integer di You can save some typing by declaring several identifiers of the same type in the same decla ration like this int a b 7 c h Note that c is a pointer to an integer since it has an asterisk at its left side This notation is somehow confusing and forgetting an asterisk is quite common Use this multiple declara tions when all declared identifiers are of the same type and put pointers in separate lines The syntax of C declarations has been criticized for being quite obscure This is true there is no point in negating an evident weakness In his book Deep C secrets Peter van der Lin den writes a simple algorithm to re
174. M Having done that we use the macro for inserting an item into the tree The root item created we should then scan the siblings and child windows of the desktop Since the desktop is the root of all windows it has no siblings so we start at its first child The GetWindow function gives us a handle to it 2 10 5 Scanning the window tree We call our Scan function with the handle of the tree control the handle to the just inserted item and the window handle of the first child that we just obtained The Scan function looks like this void Scan HWND hTree HTREEITEM hTreeParent HWND Start HWND hwnd Start hwndl TV_INSERTSTRUCT TreeCtrlitem HTREEITEM htiNewNode char bufTxt 256 bufClassName 256 Output 1024 276 C Tutorial while hwnd NULL SendMessage hwnd WM_GETTEXT 250 LPARAM bufTxt GetClassName hwnd bufClassName 250 wsprintf Output Ss Ss bufTxt bufClassName memset amp TreeCtrlitem 0 sizeof TreeCtrliItem TreeCtrlitem hParent hTreeParent TreeCtrlitem hIinsertAfter TVI_LAST TreeCtrlitem item mask TVIF_TEXT TVIF_PARAM TreeCtrlItem item pszText LPSTR Output TreeCtrlitem item 1Param LPARAM hwnd htiNewNode TreeView_InsertItem hTree amp TreeCtrliItem if hwnd1 GetWindow hwnd GW_CHILD NULL Scan hTree htiNewNode hwndl1 hwnd Get Window hwnd GW_HWNDNEXT
175. M for instance and it is maybe not compatible with some other compilers It is compatible with Microsoft compilers and maybe Borland since all of them use the same binary approach to this problem imposed by the windows API 7 Using some other mechanism of structured exception handling Many other libraries exists for structured exception handling sometimes using setjmp longjmp sometimes using the signal mechanism or some other conventions If you find yourself working with some code that does this either you use it without any modifications or you just drop it Trying to fix modify this kind of code is best left to very experienced programmers 8 Using GetLastError to get information about the error This would seem evident but in their infinite wisdom the windows API designers decided to provide different error codes for the same failures in the different versions of the operating system Under windows 95 98 the error codes would be different than the error codes for the same failure under windows NT 2000 When you mix all those error handling strategies in a single program as you have to do to pro gram with the API the resulting mix can be very entertaining Consider this extern BOOL DoSomething void Uses the boolean strategy BOOL ok DoSomething if FAILED ok WRONG return The macro FAILED tests if the HRESULT is less than zero Here is the definition define FAILED S HRESULT S lt
176. M like this typedef struct tagStream char Name long handle FILE file STREAM and we take care to erase any references to that member We eliminate the memcpy calls and that s all Our program is smaller uses less memory and what is essential does the same thing quicker than the older version since we spare the copying It is very important to learn from the beginning that software gains not only with the lines of code that you write but also with the lines of code that you eliminate 1 26 Traditional string representation in C In C character strings are represented by a sequence of bytes finished by a trailing zero byte For example if you got char Name lcc win32 You will have in memory something like this l Cc c z w i n 3 2 0 108 99 99 45 119 105 110 51 50 0 70 The standard files defined by the standard are stdin or standard input to read from the current input device the stdout or standard output and the stderr stream to show errors Initially stdin is bound to the keyboard stdout and stderr to the screen Traditional string representation inC 131 We will have at each of the position of the string array a byte containing a number the ASCII equivalent of a letter The array will be followed by a zero byte Zero is not an ASCII charac ter and can t appear in character strings so it means that the string finishes there This design is quite
177. MaxClass longest class string amp cValues number of values for this key amp cchMaxValue longest value name amp cbMaxValueData longest value data amp cbSecurityDescriptor security descriptor amp ftLastWriteTime last write time SetDlgItemText hDlg IDE_CLASS achClass SetDlgItemInt hDlg IDE_CVALUES cValues FALSE SendMessage GetDlgItem hDlg IDL_LISTBOX LB_ADDSTRING 0 LONG Enumerate the child keys until RegEnumKeyEx fails Then get the name of each child key and copy it into the list box SetCursor LoadCursor NULL IDC_WAIT for i 0 retCode ERROR_SUCCESS retCode ERROR_SUCCESS i retCode RegEnumKeyEx hKey i achKey AX_PATH NULL NULL NULL amp ftLastWriteTime if retCode DWORD ERROR_SUCCESS SendMessage GetDlgItem hDlg IDL_LISTBOX LB_ADDSTRING 0 LONG achKey SetCursor LoadCursor NULL IDC_ARROW Enumerate the key values SetCursor LoadCursor NULL IDC_WAIT if cValues for j 0 retValue ERROR_SUCCI jJ lt cValues j ti n n x cchValue MAX_VALUE_NAME achValue 0 0 retValue RegEnumValue hKey j achValue amp cchValue NULL NULL amp dawType NULL amp bData NULL amp bcData if retValue DWORD ERROR_SUCCI
178. NULL hInstance NULL if hWnd Gl return FALS ShowWindow hWnd nCmdShow UpdateWindow hWnd return TRU LRESULT CALLBACK WndProc HWND lParam hWnd UINT message WPARAM wParam FAQ 363 LPARAM switch message case WM_NCCALCSIZE CAPTURE THIS MESSAGE AND RETURN NULL return NULL case WM_CREATE SetTimer hWnd ID_TIMER_INIT 1000 NULL SetTimer hWnd ID _TIMER_LOAD 2000 NULL SetTimer hWnd ID_TIMER_DONE 4000 NULL SetTimer hWnd ID_TIMER_CLOSE 5000 NULL break case WM_PAINT PAINTSTRUCT ps 0 RECT rc 0 HDC hDC BeginPaint hWnd amp ps GetClientRect hWnd amp rc InflateRect amp rc 2 2 Rectangle hDC rec left rce top rec right rec bottom InflateRect amp rc 15 15 HFONT hFont CreateFont 35 35 0 0 0 0 0 0 0 0 0 0 0 TEXT Arial HFONT hOldFont HFONT SelectObject hDC hFont DrawText hDC SZ_SPLASH lstrlen SZ_SPLASH amp rc DT _WORDBREAK SelectObject nDC hOldFont EndPaint hWnd amp ps break case WM_DESTROY PostQuitMessage 0 break case WM_TIMER HDC hDC GetDC hWnd RECT rc te LOS 4S GetClientRect hWnd amp rc KillTimer hWnd Param switch m py wW wParam F case ID_TIMER_
179. Param 120 You may wonder what that variable msg stands for It is a structure of type MSG that is defined in windows h as follows typedef struct tagMSG HWND hwnd UINT message WPARAM wParam LPARAM lParam DWORD time POINT pt MSG PMSG NPMSG LPMSG Note that in C you can append as many names to a pointer to a structure as you like and in windows this is used a lot The reason is an historical one In windows 16 bits there were several types of pointers near 16 bit pointers far long pointers of 32 bits and generally the near pointers were prefixed with NP the 32 bit ones with LP This was retained for compatibility reasons until today even if there are only 32 bit pointers now This structure contains then the following fields e hwnd The handle of the specific window to which the message is directed e message A 16 bit value identifying the message e wparam A 32 bit value identifying the first message parameter Its meaning depends on the message being sent e Param A 32 bit value identifying the second message parameter e time A 32 bit value identifying the time when the event that provoked this message happened e pt This is a POINT structure containing the coordinates of the mouse in the instant the event happened that provoked this message 262 C Tutorial return 0 Having all this menues in place is nice but if you are used to use the keyboard som
180. Programming with loc win by Jacob Navia and Q Software Solutions GmbH Acknowledgements Thanks to all people that have contributed to this work Thanks to the many people that sent me those bug reports that allowed me to improve the software To all that sent me messages of encouragement Thanks specially to Friedrich Dominicus J ohn Findlay and Mike Caetano among many other people that collaborated to make Icc win what it is today 2000 2006 Jacob Navia and Q Software Solutions GmbH This document is part of the Icc win documentation Distribution in any form is explicitly not allowed Chapter 1 Introduction to C 1 Why learn C 1 Program organization 2 Hello 3 Program input 4 What are function parameters 5 Console mode programs and windows programs 6 An overview of the compilation process 6 The run time environment 7 An overview of the standard libraries 9 The stdheaders h include file 9 Passing arguments to a program 10 Iteration constructs 13 for 13 while 14 do 14 Types 15 What is a type 15 Types classification 16 Integer types 17 Floating types 17 Compatible types 17 Incomplete types 18 Qualified types 18 Casting 18 The basic types 19 Declarations and definitions 20 Variable declaration 21 Function declaration 23 Function definitions 24 Scope of identifiers 24 Linkage and duration of objects 24 Variable definition 25 Statement syntax 25 Errors and warnings 25 Input and output 27 Pred
181. RegisterClassEx function that was added to Windows 95 It is important to call this function so that the application will get well formed small icons associated with it ATOM MyRegisterClass HINSTANCE hInstance WNDCLASSEX wcex wcex cbSize sizeof WNDCLASSEX wcex style CS_HREDRAW CS_VREDRAW wcex lpfnWndProc WNDPROC WndProc wcex cbClsExtra 0 wcex cbWndExtra 0 wcex hInstance hiInstance wcex hIcon NULL wcex hCursor LoadCursor NULL IDC_ARROW wceex hbrBackground HBRUSH COLOR_WINDOW 1 wcex lpszMenuName NULL wcex lpszClassName SplashWndClass wcex hIconsm NULL return RegisterClassEx amp wcex Fy me FUNCTION InitInstance HANDLE int PURPOSE Saves instance handle and creates main window JE VvV n this function we save the instance handle in a global ariable and create and display the main program window BOOL InitInstance HINSTANCE hInstance int nCmdShow HWND hWnd RECT rect int splashwidth 350 int splashheight 350 hInst hInstance Store instance handle in this global variable SystemParametersInfo SPI_GETWORKAREA 0 LPVOID amp rect 0 hWnd CreateWindowEx WS_EX_TOOLWINDOW SplashWndClass NULL WS_OVERLAPPED rect right rect left splashwidth 2 rect bottom rect top splashheight 2 splashwidth splashheight NULL
182. S countchars c Author Jacob Project Tutorial examples State Finished Creation Date July 2000 Description This program opens the given file and 34 C programming with Icc win32 prints the number of characters in it include lt stdio h gt include lt stdlib h gt int main int argc char argv The skeleton of the commentary above is generated automatically by the IDE Just right click int count 0 FILE infile int c if arge lt 2 printf Usage countchars lt file name gt n exit EXIT_FAILURE infile fopen argv 1 rb if infile NULL printf File s doesn t exist n argv 1 exit EXIT_FAILURE c fgetc infile while c EOF count c fgetc infile fclose infile printf d n count return 0 somewhere in your file and choose edit description Summary e A program is defined by its specifications In this example counting the number of characters in a file e A first working version of the specification is developed Essential parts like error checking are missing but the program works for its essential function e Error checking is added and test cases are built e The program is examined for correctness and the possibility of memory leaks unclosed files etc is reviewed Comments are added to make the purpose of the program clear and to allow other people know what it does without being forced to re
183. SE result We have to clean up the structure note that this is a local variable so its contents are as yet undefined We use the primitive memset and set all members of the structure to zero This is a common idiom in C clear all memory before using and assign to it a known value Since the default value of many structure members is zero this easies the initialization of the structure since we do not have to explicitly set them to NULL or zero We start the filling of the relevant members We need to put the owner window handle in the hwndOwner member We get the handle of the current active window using a call to a win dows API The shell needs place to store the display name of the chosen path Note that this is not what we want the full path but just the last item in the path i e the last directory Why this is so Because the user could choose a path like My documents and in this case we could detect that the user has chosen a standard well known name for the directory But we do not use Advanced windows techniques 327 this feature and just give the shell some place in our result variable Since we overwrite this data later this is harmless and avoids a new variable 3 We set the IpszTitle member to the value we passed in This is a text that will be displayed at the top of the user interface window that appears and should remain the user what kind of folder he she is looking for As flags w
184. ScanWord int firstchar FILE f int i 1 index for the word buffer c 0 Character read char idbuf MAXIDLENGTH 1 Buffer for the word idbuf 0 firstchar We have at least one char c fgetc f Read the next one while isWordStart c c gt 0 amp amp c lt 9 idbuf it c Store it in the array if i gt MAXIDLENGTH Check for overflow fprintf stderr Identifier too long n return 0 Returning zero will break the loop in the calling function c fgetc f Scan the next char idbuf i 0 Always zero terminate EnterWord idbuf Enter into the table return 1 OK to go on We hold the index into our array in the identifier i for index It starts at one since we receive already the first character of a word Note that we test with this index if we are going to over flow our local table idbuf We said before that error checking should be abstracted when designing the program but as any rule that one has exceptions If we were going to leave a lot of obvious errors in many functions around we would need a lot of work later on to fix all those errors Fundamental error checking like a buffer overrun should always be in our minds from the beginning so we do it immediately Note that this test is a very simple one 1 31 1 The organization of the table Now we have no choice but to start thinking about that EnterWord function All the eas
185. SetValueEx hkey Path 0 REG_EXPAND_SZ buf siz ERROR_SUCCESS RegCloseKey hKey return ERROR_ACCESS_DENIED RegCloseKey hkey Send a message to all windows telling them that the Path environment variable has changed SendMessageTimeout HWND_BROADCAST WM_SETTINGCHANGE 0 LPARAM Environment SMTO_ABORTIFHUNG 5000 amp dwReturnValue return dwReturnValue 2 22 19 How do I add a menu item to the explorer right click menu When you press the right mouse button within the explorer window there is a pop up menu that shows you a series of options like Explore Open etc To add an entry to this menu you just add your new menu item name to HKEY_CLASSES_ROOT Directory shell YourItemName The value of this key should be a text string containing the menu item name Then you add a subkey called command that specifies the command to be executed To take a concrete and simple example we want to start a command shell in the directory where the mouse is pointing to We prepare a text file to add this keys using notepad or another text edi tor EGEDIT4 HKEY_CLASSES_ROOT Directory shell CmdHere CMD amp Prompt Here HKEY_CLASSES_ROOT Directory shell CmdHere command G WINDOWS System32 cmd exe k cd S1 R e e FAQ 371 We call the program regedit wi
186. The maximum value for the number of devices that can be simultaneously con nected is given by the macro FOPEN_MAX defined in stdio h Under systems with a graphical user interface GUI you do not have these devices available or they are avilable but not visible Most of those systems allow you to open a command line window that acts like a primitive system console with a text mode interface When you use those command line windows your program has this standard devices available 34 The text mode window is often called Dos window even if it has nothing to do with the old MSDOS operating system It is a window with black background by default where you can see only text no graphics Most of the examples following use this window To start it you just go to Start then Run and type the name of the command shell cmd exe Input and output 29 1 9 2 The typical sequence of operations To establish a connection with a device we use the fopen function that returns a pointer to a newly allocated FILE structure or NULL if the connection with the device fails for whatever reason Once the connection established we use fwrite fread to send or receive data from to the device When we do not need the connection any more we break the connection by closing the file include lt stdio h gt int main int argc char argv unsigned char buffer 2048 unsigned int byteswritten bytesread Error c
187. This clock will overflow in something like 2 000 years so be prepared for windows 4 000 int int int int int int Time and Date functions 159 tm_mday tm_mon tm_year tm_wday tm_yday tm_isdst The fields are self explanatory The structure timeb is defined in the directory include sys as follows struct t imeb time_t time unsigned short pad0 unsigned long lpado unsigned short millitm Fraction of a second in ms unsigned short padl unsigned long lpad1 Difference minutes moving westward between UTC and local time short timezone unsigned short pad2 unsigned long lpad2 Nonzero if daylight savings time is currently in effect for the local time zone short dstflag We show here a small program that displays the different time settings include include include include include void mai lt time h gt lt stdio h gt lt sys types h gt lt sys timeb h gt lt string h gt n char tmpbuf 128 ampm AM time_t ltime struct _timeb tstruct struct tm today gmt xmas 0 0 12 25 11 Display operating system style date and time strt ime tmpbuf printf OS time t t t t s n tmpbuf strdate tmpbuf printf OS date t t t t s n tmpbuf Get UNIX style time and display as number and string time amp ltime printf Time in seconds since UTC 1 1 70 t ld n printf UNIX time and date
188. Tutorial 2 16 The Registry The registry stores data in a hierarchically structured tree Each node in the tree is called a key Each key can contain both sub keys and values Sometimes the presence of a key is all the data that an application requires other times an application opens a key and uses the values associated with the key A key can have any number of values and the values can be in any form Registry values can be any of the following types e Binary data e 32 bit numbers e Null terminated strings e Arrays of null terminated strings The array ends with two null bytes e Expandable null terminated strings These strings contain variables like SPATH or Swindir that are expanded when accessed 2 16 1 The structure of the registry To view and edit the registry you can use the system tool regedit When it starts it shows the basic structure of the root trees amp Registry Editor File Edit view Favorites Help a SS My Computer a Sy HKEY_CLASSES_ROOT E HKEY_CURRENT_USER h E HKEY_LOCAL MACHINE E Data value not set REG_SZ E HKEY_USERS E HKEY_CURRENT_CONFIG My Computer HKEY_CLASSES_ROOT 1 HKEY_CLASSES_ROOT Registry entries under this key define types or classes of documents and the properties associated with those types Shell and COM applications use the information stored under this key File viewers and user interface extensions store their OLE class identifie
189. ULL printf tError s lpMsgBuf LocalFree lpMsgBuf Show the information for the ip address table MIB_IPADDRTABLE pIPAddrTable DWORD dwSize struct in_addr IPAddr char striIPAddr pIPAddrTable malloc sizeof MIB_IPADDRTABLI dwSize 0 IPAddr S_un S_addr ntohl pIPAddrTable gt table 1 dwAddr strIPAddr inet_ntoa IPAddr rc GetIpAddrTable pIPAddrTable amp dwSize 0 if rc ERROR_INSUFFICIENT_BUFFER free pIPAddrTable plIPAddrTable malloc dwSize Pl Ve dwRetVal GetIpAddrTable pIPAddrTable amp dwSize 0 if dwRetVal NO_ERROR printf Call to GetIpAddrTable failed nError d n GetLastError return 1 Now show the information printf Address x n pIPAddrTable gt table 0 dwAddr unsigned int mask pIPAddrTable gt table 0 dwMask printf Mask d 0 d d n Oxff amp mask Oxf f amp mask gt gt 8 Oxff amp mask gt gt 16 0xff amp mask gt gt 24 printf Index Sld n pIPAddrTable gt table 0 dwIndex printf BCast Sld n pIPAddrTable gt table 0 dwBCastAddr printf Reasm Sld n pIPAddrTable gt table 0 dwReasmSize Get the statistics about IP usage MIB_IPSTATS pStats pStats MIB_IPSTATS malloc sizeof MIB_IPSTATS if dwRetVal GetIpStatistics pStat
190. Wins printf t tPrimary Wins Server t s n pAdapter gt PrimaryWinsServer IpAddress String printf t tSecondary Wins Server t s n pAdapter gt SecondaryWinsServer IpAddress String else printf tHave Wins No n pAdapter pAdapter gt Next We query now the interface information IP_INTERFACE_INFO pInfo pinfo IP_INTERFACE_INFO malloc sizeof IP_INTERFACE_INFO rc GetInterfacelInfo piInfo amp ulOutBufLen if rc ERROR_INSUFFICIENT_BUFFER free pinfo pinfo IP_INTERFACE_INFO malloc ulOutBufLen printf ulLen ld n ulOutBuflLen else printf GetInterfaceInfo failed with error d n GetLastError return 1 dwRetVal GetInterfacelInfo piInfo amp ulOutBufLen if dwRetVal NO_ERROR printf Adapter Name S n piInfo gt Adapter 0 Name printf Adapter Index ld n pInfo gt Adapter 0 Index printf Num Adapters ld n pInfo gt NumAdapters Instead of printing a more or less meaningless error message we can use FormatMessage to give a more comprehensible description of the problem if dwRetVal LPVOID lpMsgBuf Querying the network parameters if FormatMessage FORMAT MESSAGE ALLOCATE BUFFER FORMAT_MESSAGE_FROM_SYSTEM FORMAT _ MESSAGE _IGNORE_INSERTS NULL dwRetVal MAKELANGID LANG_NEUTRAL SUBLANG_DEFAULT LPTSTR amp lpMsgBuf 0 N
191. You can sort an array using the qsort function 1 19 Pointers and references Pointers are one of the hard subjects of the C language They are somehow mysterious quite difficult for beginners to grasp and their extensive use within C makes them unavoidable Pointers are machine addresses i e they point to data It is important to have clear this distinc tion pointers are NOT the data they point to they contain just a machine address where the data will be found When you declare a pointer like this FILE infile you are declaring reserve storage for a machine address and not a FILE structure This machine address will contain the location where that structure starts This allows us to pass a small machine address around instead of a big FILE structure that has dozens of fields The big advantage of pointers is that they are efficient But as anything they are error prone There is no free lunch The contents of the pointer are undefined until you initialize it Before you initialize a pointer its contents can be anything it is not possible to know what is in there until you make an assignment A pointer before is initialized is a dangling pointer i e a pointer that points to nowhere A pointer can be initialized by 1 Assign it a special pointer value called NULL i e empty 2 Assignment from a function or expression that returns a pointer of the same type In the frequencies example we initialize our infile poin
192. _WIN32_NT 2 21 2 Translating the value returned by GetLastError into a readable string This utility function uses the system FormatMessage to do the bulk of the work of caring about locale settings like language setup etc BOOL GetFormattedError LPTSTR dest int size DWORD dwLastError GetLastError if dwLastError return 0 BYTE width 0 DWORD flags flags FORMAT MESSAGE MAX WIDTH _MASK amp width flags FORMAT_MESSAGE_FROM_SYSTEM flags FORMAT_MESSAGE_IGNORE_INSERTS return 0 FormatMessage flags NULL dwLastError MAKELANGID LANG_NEUTRAL SUBLANG DEFAULT dest size NULL 2 21 3 Clearing the screen in text mode The following code will clear the screen in text mode include lt windows h gt Standard error macro for reporting API errors define PERR bSuccess api if bSuccess printf s Error d from s on line d n __FILE__ GetLastError api __LINE_ void cls HANDLE hConsole COORD coordScreen 0 0 Home the cursor here BOOL bSuccess DWORD cCharsWritten CONSOLE_SCREEN_BUFFER_INFO csbi to get buffer info DWORD dwConSize number of character cells in the current buffer get the number of character cells in the current buffer bSuccess GetConsoleScreenBufferInfo hConsole amp csbi
193. a 6 int i 0 i lt 10 i t is allowed but NOT for int i 0 StructF a 67 i lt 10 i Syntax error 1 5 2 while The while construct is much more simple It consists of a single test that determines if the loop body should be executed or not There is no initialization part nor increment part The general form is while test statement block Any for loop can be transformed into a while loop by just doing init while test statement block increment 1 5 3 do The do construct is a kind of inverted while The body of the loop will always be executed at least once At the end of each iteration the test is performed The general form is do statement block while test Using the break keyword can stop any loop This keyword provokes an exit of the block of the loop and execution continues right afterwards The continue keyword can be used within any loop construct to provoke a jump to the end of the statement block The loop continues normally only the statements between the continue keyword and the end of the loop are ignored Types 15 1 6 Types A machine has no concept of type everything is just a sequence of bits and any operation with those sequences can be done even if it is not meaningful at all for example adding two addresses or multiplying two character strings A high level programming language however enforces the concept of types of da
194. a separate key Storing the data in binary form allows an application to store data in one value that would otherwise be made up of several incompatible types 312 C Tutorial 2 16 4 Interesting keys The registry is an endless source of useful tips There is for instance a nice site that provides Functionality Key Change the Location of System and HKEY_CURRENT_USER Software Microsoft Win Special Folders dows CurrentVersion Explorer User Shell Folders Configure CoolSwitch Application HKEY_CURRENT_USER Control Panel Desktop Swapping Value Name CoolSwitch CoolSwitchColumns CoolSwitch is a feature available Cools witek Rows within Windows to quickly switch between tasks and programs by using the Alt TAB keys Value Data 0 disabled 1 enabled Modify the value named CoolSwitch and set it to 0 to disable task switching or 1 to enable it Data Type REG_SZ String Value To change the size of the CoolSwitch popup modify the val ues named CoolSwitchColumns and CoolSwitchRows Logoff or restart Windows for the changes to take effect Change the Registered Owner and Windows 95 98 Organization HKEY_LOCAL_MACHINE SOFTWARE Microsoft Win dows CurrentVersion Windows NT 2000 XP HKEY_LOCAL_MACHINE SOFTWARE Microsoft Win dows NT Current Version Change the version of the Icc win HKEY_CURRENT_USER software lcc compiler to a new location or to an older newer version Di
195. ackbar is a window that contains a slider and optional tick marks When the user moves the slider using either the mouse or the direc tion keys the trackbar sends notification messages to indicate the change The notifications used are only the NU_CUSTOMDRAW and the NUV_REALEASEDCAPTURE messages Tree views A tree view control is a window that displays a hierarchical list of items such as the headings in a document the entries in an index or the files and directories on a disk Each item consists of a label and an optional bitmapped image and each item can have a list of sub items associated with it By clicking an item the user can expand or collapse the associated list of subitems The notifications sent use the TVN_XXX prefix Up down control An up down control is a pair of arrow buttons that the user can click to increment or decrement a value such as a scroll position or a num ber displayed in a companion control The value associated with an up down control is called its current position An up down control is most often used with a companion control which is called a buddy window The documentation for all this controls is very detailed and it would be impossible to repro duce here Note that many of the controls not directly supported in the resource editor can be created by hand by just calling the CreateWindow procedure Most of them are not spe cially useful in the context of a dialog box T
196. ad the program text 1 9 4 1 9 4 1 Each open file descriptor has a current position i e the position in the data stream where the next write or read operation will be done To know where the file pointer is use the fte11 Other input output functions The current position function To set the current position to some specific index use the fseek function Here is an example of the usage of those functions We write a function that will return the length of a given file The algorithm is very simple 1 Set the file pointer at the end of the file Input and output 35 2 Read the position of the file cursor This is the size of the file Easy isn t it unsigned int FileLength char FileName FILE f fopen FileName rb 1 int result if f NULL return 3 if fseek f 0 SEEK_END 2 fclose f return 2 result ftell f 3 fclose f return result 4 1 We open the file Note that we open it in binary mode because ftell and fseek will NOT work with files opened in text mode where the sequence r n is translated into only one character 2 The fseek function will position the file pointer The first argument is the file descriptor pointer the second is the distance from either the beginning the current position or the end of the file In our example we use the position from the end of the file SEEK_END If the function fails for some reason we return 2
197. ad them He proposes chapter 3 the following The Precedence Rule for Understanding C Declarations Rule 1 Declarations are read by starting with the name and then reading in precedence order Rule 2 The precedence from high to low is 2 A Parentheses grouping together parts of a declaration 2 B The postfix operators 2 B 1 Parentheses indicating a function prototype and 2 B 2 Square brackets indicating an array 2 B 3 The prefix operator the asterisk denoting pointer to Rule 3 If a const and or volatile keyword is next to a type specifier e g int long etc it applies to the type specifier Otherwise the const and or volatile keyword applies to the pointer asterisk on its immediate left Using those rules we can even understand a thing like char const next int a int b We start with the variable name in this case next This is the name of the thing being declared We see it is in a parenthesized expression with an asterisk so we conclude that next is a pointer to well something We go outside the parentheses and we see an asterisk at the left and a function prototype at the right Using rule 2 B 1 we continue with the prototype next is a pointer to a function with two arguments We then process the asterisk next is a pointer to a function with two arguments returning a pointer to Finally we add the char const to get next is a pointer to a function with two argu
198. adapt memory consumption to the actual needs of the program The static buffers could be either over dimensioned wasting memory space or not enough to hold the data needed Since the static buffers must be patterned after the biggest possible input they will be over dimensioned for the average case 2 Unless programming is adapted to this strategy it is difficult to reuse memory being used in different buffers to make space for a temporary surge in the space needs of the program 1 30 2 Stack based allocation The C standard allows for this when you write int fn int a char workspace 10000 In this case the compiler generates code that allocates 10000 bytes of storage from the stack This is a refinement of the static buffers strategy Under the windows operating system the stack is IMB in normal programs but this can be increased with a special linker option A variant of this strategy allows for dynamic allocation Instead of allocating a memory block of size siz with malloc we can write char workspace siz and the compiler will generate code that allocates siz bytes from the program stack Advantages 1 Very fast allocation and deallocation To allocate a memory block only a few assembly instructions are needed Deallocation is done without any extra cost when the function where the variables are located exits Drawbacks 1 There is no way to know if the allocation fails If the stack has reached its ma
199. add a fourth scope for function labels that are visible anywhere within a function without any restriction of block scopes 1 7 5 Linkage and duration of objects The linkage of an object is whether it is visible outside the current compilation unit or not Objects that are marked as external or appear at global scope without the keyword static are visible outside the current compilation unit Note that an identifier that doesn t refer to an object can have global scope but not be visible outside the current compilation unit Enumera tions for instance even if they have global scope are not exported to other modules In general we have the public objects visible in all modules of the program and the private ones marked with the keyword static and visible only in the current compilation unit 31 There is a strong commitment from the part of the compiler writers to maintain the code that was written in the language and to avoid destroying programs that are working When the standards committee proposed the prototypes all C code wasn t using them yet so a transition period was set up Compilers would accept the old declarations without prototypes and just emit a warning Some people say that this period should be over by now it is more than 10 years that we have prototypes already but still new compilers like Icc win are supporting old style declarations Errors and warnings 25 The duration of an object mea
200. ain without arguments and with arguments and arguments lt args gt return x 1 This is a qualifier that applies to functions If double inline present it can be understood by the compiler as overPi double a inline a specification to generate the fastest function call possible generally by means of replicating return a 3 14159 the function body at each call site This is the entry point of each program There should be a single function called main in each int main void main conforming C program There are two possible int main int argc char argv 38 Lcc win recognizes but doesn t yet implement the keyword restrict An overview of the whole language 45 1 11 3 Pre processor commentary Double slashes introduce comments up to the end of the line see Comments on page 64 comment commentary Slash star introduces a commentary until the sequence star slash is seen see Comments on page 64 comment defined id If the given identifier is defined return 1 else return 0 if defined max define id text Replace all appearances of the given identifier by the corresponding expression See Preprocessor commands on page 169 define TAX 6 Define a macro with n arguments When define max a b define macro a b used the arguments are lexically a lt b replaced within the macro S
201. aking the changes the environment variables will reflect the previous not the current values The changes do not take effect until you log off and then log back on To effect these changes without having to log off broadcast a WM_SETTINGCHANGE mes sage to all windows in the system so that any interested applications such as Program Man ager Task Manager Control Panel and so forth can perform an update For example on Windows NT the following code fragment should propagate the changes to the environment variables used in the Command Prompt SendMessageTimeout HWND_BROADCAST WM_SETTINGCHANGE 0 LPARAM Environment SMTO_ABORTIFHUNG 5000 amp dwReturnValue None of the applications that ship with Windows 95 including Program Manager and the shell respond to this message Thus while this article can technically be implemented on Windows 95 there is no effect except to notify third party applications The only method of changing global environment variables on Windows 95 is to modify the autoexec bat file and reboot 2 22 18 How do I add a new directory to the PATH variable permanently The problem with the standard function putenv is that once the program that called it is fin ished the environment reverts to its default state Here is a utility that will add a new directory to the Path environment variable permanently The algorithm modifies the registry key HKEY_CURRENT_USER Environment P
202. al 2 21 19 Accessing the disk drive directly without using a file system To open a physical hard drive for direct disk access raw I O in a Windows based application use a device name of the form PhysicalDriveN where N is 0 1 2 and so forth representing each of the physical drives in the system To open a logical drive direct access is of the form X where X is a hard drive partition letter floppy disk drive or CD ROM drive You can open a physical or logical drive using the CreateFile application programming inter face API with these device names provided that you have the appropriate access rights to the drive that is you must be an administrator You must use both the CreateFile FILE_SHARE_READ and FILE_SHARE_WRITE flags to gain access to the drive Once the logical or physical drive has been opened you can then perform direct I O to the data on the entire drive When performing direct disk I O you must seek read and write in multi ples of sector sizes of the device and on sector boundaries Call DeviceloControl using IOCTL_DISK_GET_DRIVE_GEOMETRY to get the bytes per sector number of sectors sectors per track and so forth so that you can compute the size of the buffer that you will need Note that a Windows based application cannot open a file by using internal Windows NT object names for example attempting to open a CD ROM drive by opening Device CdRom0 does not work because this is not a v
203. al and binary 5 left to right logical or binary 4 left to right Pas conditional binary 2 right to left H k lt lt gt gt assignment binary 2 right to left amp sequential evaluation binary 1 left to right The printf family 75 1 14 The printf family The functions fprintf printf sprintf and snprintf are a group of functions to output formatted text into a file fprintf printf or a character string sprintf The snprintf is like sprintf func tion but accepts a count of how many characters should be put as a maximum in the output string Function Prototype fprintf int fprintf FILE stream const char fmt printf int printf const char fmt sprintf char outputstring const char fmt snprintf int snprintf char out size_t maxchars const char fmt The printf function is the same as fprintf with an implicit argument stdout i e the standard output of the program that in most cases is the console window fprintf stdout hello n lt gt printf hello n The value returned by all this functions is EOF End Of File usually 1 if an error occurred during the output operation Otherwise all went OK and they return the number of characters written For sprintf the returned count does not include the terminating zero appended to the output string The fmt argument is a character string or control s
204. alent routines This is also a dynamic data area it grows when we allocate memory using malloc and shrinks when we release the allocated memory with the free library function There is no action needed from your side to manage the initial data area or the stack The com piler takes care of all that The program however manages the heap i e the run time system expects that you keep book exactly and without any errors from each piece of memory you allocate using malloc This is a very exhausting undertaking that takes a lot of time and effort to get right Things can be easy if you always free the allocated memory before leaving the function where they were allo cated but this is impossible in general since there are functions that precisely return newly allocated memory for other sections of the program to use There is no other solution than to keep book in your head of each piece of RAM Several errors all of them fatal can appear here e You allocate memory and forget to free it This is a memory leak e You allocate memory and you free it but because of a complicated control flow many ifs whiles and other constructs you free a piece of memory twice This corrupts the whole memory allocation system and in a few milliseconds all the memory of your program can be a horrible mess e You allocate memory you free it once but you forget that you had assigned the memory pointer to another pointer or left it in a structure etc
205. alid Win32 device name You can use the QueryDosDe vice API to get a list of all valid Win32 device names and see the mapping between a par ticular Win32 device name and an internal Windows NT object name An application running at a sufficient privilege level can define redefine or delete Win32 device mappings by calling the DefineDosDevice API 2 21 20 Retrieving the Last Write Time The following example uses the GetFileTime function to retrieve the last write time for a file It converts the time to local time based on the current time zone settings and creates a date and time string that can be shown to the user BOOL GetLastWriteTime HANDLE hFile LPSTR String FILETIME ftCreate ftAccess ftWrite SYSTEMTIME stUTC stLocal Retrieve the file times for the file if GetFileTime hFile amp ftCreate amp ftAccess amp ftWrite return FALSE Convert the last write time to local time FileTimeToSystemTime amp ftWrite amp stUTC SystemTimeToTzSpecificLocalTime NULL amp StUTC amp stLocal Build a string showing the date and time sprintf String 02d 02d d 02d 02d stLocal wDay stLocal wMonth stLocal wYear stLocal wHour stLocal wMinute Some Coding Tips 345 return TRUE 2 21 21 Retrieving the file name from a FILE pointer The algorithm consists of several steps 1 Take care of trivial cases the predefined files st
206. all it anywhere you want it will always return the exception code of the last exception that was executed or zero if there weren t any 184 C programming with Icc win32 Another useful function is void RaiseException unsigned code unsigned flags unsigned nbArgs unsigned args We can use it to call the exception handling mechanism in the same way as a real exception would Example include lt stdio h gt include lt seh h gt int main void char p 10 unsigned code __try p 0 printf No exceptions n RaiseException Oxdeadbeef 0 0 NULL _ except code GetExceptionCode EXCEPTION_EXECUTE_HANDLER printf Ooops there was a problem with this program n printf Error code x n code return 0 This will print No exceptions Ooops there was a problem with this program Error code Oxceadbeef Note that the system will change the exception code from 0xdeadbeef to Oxceadbeef Why The explanation is in the MSDN site 83 I quote To make sure that you do not define a code that conflicts with an existing exception code set the third most significant bit to 1 The four most significant bits should be set as shown in the following table Bits Recommended Description setting 31 30 11 These two bits describe the basic status of the code 11 error 00 success 01 informational 10 warning 29 1 Client bit Set to 1 for user defined codes 28 0 Reserved
207. alloc sizeof mem MEM_ALLOC_SIZE if mem NULL fprintf stderr No more memory at line d n line exit EXIT_FAILURE 156 C programming with Icc win32 mem gt used 0 memoryused MEM ALLOC_ SIZE mem gt size MEM ALLOC SIZE result mem gt memory mem gt used mem gt used siz memset result siz 0 memoryused siz return result We use a Static pointer to a MEMORY structure to hold the location of the current memory chunk being used Since it is static it will be initialized to NULL automatically by the compiler and will keep its value from one call to the next We test before using it if the chunk has enough room for the given memory size we want to allocate or if it is NULL i e this is the very first word we are entering If either of those if true we allocate a new chunk and initialize its fields Otherwise we have some room in our current chunk We increase our counters and return a pointer to the position within the memory field where this chunk starts We clean the mem ory with zeroes before returning it to the calling function Note that we do not keep any trace of the memory we have allocated so it will be impossible to free it after we use it This is not so bad because the operating system will free the memory after this program exists The downside of this implementation is that we can t use this pro gram within another one that would call our word counting routine We h
208. allocation problems plague also other languages like C that use a similar schema than C Memory management and memory layout 143 1 29 1 Functions for memory allocation malloc Returns a pointer to a newly allocated memory block free Releases a memory block calloc Returns a pointer to a newly allocated zero filled memory block realloc Resizes a memory block preserving its contents alloca Allocate a memory block in the stack that is automatically destroyed when the function where the allocation is requested exits In some other compilers this function may be absent GC malloc Allocates a memory block managed by the memory manager In some other compilers this function may not be present 1 29 2 Memory layout under windows A 32 bit address can be used to address up to 4GB of RAM From this potential address space windows reserves for the system 2GB leaving the other 2GB for each application These addresses of course are virtual since not all PCs have 2GB of real RAM installed To the windows memory manager those numbers are just placeholders that are used to find the real memory address Each 32 bit address is divided in three groups two containing 10 bits and the third 12 bits 22 21 12 11 0 3 The translation goes as follows The higher order bits 31 21 are used to index a page of memory called the page directory Each process contains its own page directory filled with 1024 numb
209. amp amp dirdata cFileName 1 0 dirdata cFileName 1 We change the current dir to the subdir and recurse chdir dirdata cFileName ScanFiles spec fn Restore current directory to the former one chdir dir while FindNextFile hdir amp dirdata FindClose hdir return 1 This function above could be used in a program like this static int files used to count the number of files seen This is the callback function It will print the name of the file and increment a counter int printfile char fname printf s n fname files return 1 main expects a specification and possibly a starting directory If no starting directory is given it will default to the current directory 176 C programming with Icc win32 Note that many error checks are absent to simplify the code No validation is done to the result of the chdir function for instance int main int argc char argv char spec MAX PATH char startdir MAX PATH if argc 1 printf scan files expects a file spec n return 1 memset startdir 0 sizeof startdir memset spec 0 sizeof spec strncpy spec argv 1 sizeof spec 1 if argc gt 2 strcpy startdir argv 2 if startdir 0 0 getcwd startdir sizeof startdir 1 chdir startdir files 0 ScanFiles spec printfile printf d files n files return 0
210. an t hold this value the result is that the initialization will not work at all 40 1 13 2 4 Character string constants For character string constants they are enclosed in double quotes If immediately before the double quote there is an L it means that they are double byte strings Example L abc This means that the compiler will convert this character string into a wide character string and store the values as double byte character string instead of just ASCII characters To include a double quote within a string it must be preceded with a backslash Example The string the string is enclosed in quotes Note that strings and numbers are completely different data types Even if a string contains only digits it will never be recognized as a number by the compiler 162 is a string and to convert it to a number you must explicitly write code to do the transformation 39 Qfloats are an extension of Icc win 40 lcc win will emit a warning overflow in floating constant but other compilers may not A closer view 51 Within the string the following abbreviations are recognized Abbreviation Meaning Value n New line 10 r carriage return 12 b backspace 8 v vertical tab 11 t tab 9 f form feed 12 e escape 27 a bell 7 backslash Add a double quote S Insert at the current position the Any since any digit can be x lt hex digits gt character with t
211. ancient and dates to the beginning of the C language It has several flaws as you can immediately see e There is no way to know the length of a string besides parsing the whole character array until a zero byte is found e Any error where you forget to assign the last terminated byte or this byte gets overwritten will have catastrophic consequences e There is no way to enforce indexing checks The most frequently used function of this library are strlen that returns an integer containing the length of the string Example int len strlen Some character string Note that the length of the string is the number of characters without counting the trailing zero The physical length of the string includes this zero byte however and this has been and will be the source of an infinite number of bugs strcmp that compares two strings If the strings are equal it returns zero If the first is greater in the lexicographical sense than the second it returns a value greater than zero If the first string is less than the second it returns some value less than zero The order for the strings is based in the sequence of characters in the current character set a b stremp a b a lt b stremp a b lt 0 a gt b stremp a b gt 0 strcpy copies one string into another strcpy dst src copies the src string into the dst string This means it will start copying characters from the beginning of the src locati
212. and at first it looks like a normal exception Consider this program include include include include lt windows h gt lt seh h gt lt stdio h gt lt intrinsics h gt void StackOverflow int depth char blockdata 90000 printf Overflow d n depth StackOverflow depth 1 int main int argc char argv for try StackOverflow 0 _ except EXCEPTION_EXECUTE_HANDLER printf Exception handler 1x n GetExceptionCode return 0 When run this program will print Overflow Overflow Overflow Overflow Overflow Overflow Overflow Overflow Overflow Overflow Overflow 0 1 2 3 4 5 6 7 8 9 10 Exception handler C00000FD Overflow Overflow Overflow Overflow Overflow Overflow Overflow Overflow Overflow Overflow Overflow 0 Po WANA U BWNHEe 0 We see that the first time the handler is invoked but the second time there is no handler invoked the program exits abruptly without any further messages The reason for this behavior is that if a thread in your application causes an EXC EPTION_STACK_OVERFLOW then your thread has left its stack in a damaged state This is in Advanced C programming with Icc win 187 contrast to other exceptions such as amp EXCEPTION_ACCESS_VIOLATION or EXCEPTION_INT_DIVIDE_BY_ZERO where the stack is not damaged This is because the stack is set to an ar
213. appear when you right click in a button Those dialog boxes have generally a standard or Properties part that allows you to change things like the element s text or other simple properties and a part that is visible only when you have selected the C code generation That part is normally labeled events and appears at the right That label tells us which kind of events the framework supports window messages There are many events that can possibly happen of course but the framework handles only those Push button 1 Properties LoginDlgId0k MS Sans Serif Font size Clicked We see at the right tab a typical messages part We have some buttons to choose the mes sages we want to handle the function name prefix we want for all callback procedures for this element and other things like the font we want to use when the elements are displayed We see again that Dlg400 but this allows us to explain how those names are generated actually The names of the generated functions are built from the prefix of the dialog box then the prefix for the element and then a fixed part that corresponds to the event name We edit the prefix again following this convention Push button 1 x Properties Events LoginDlgId0k MS Sans Serif Font size Clicked The Selected message is on so the framework will generate a call to a function called D1g SearchOnOkSeelected Happily for us we do not have to
214. are their prototype to the compiler so that the right code will be generated for them An unprototyped function returning a double will surely result in incorrect results Opaque data structures are hidden from client code code that uses them by providing just a void pointer to them This way the client code is not bound to the internal form of the Filling the blanks 287 structure and the designers of the system can modify it without affecting any code that uses them Most of the windows data structures are used this way an opaque HANDLE is given that discloses none of the internals of the object it is pointing to 2 12 Filling the blanks Input goes through dialog boxes under windows They are ubiquitous so let s start to fill our skeleton with some flesh Let s suppose for the sake of the example that we want to develop a simple text editor It should read some text draw it in the screen and provide some utilities like search replace etc First we edit our menu and add an edit item We open the directory window and select the menu B 63 Menus o e IDMAINMENU J Strings Accelerator We arrive at the menu editor If we open each branch of the tree in its left side it looks like this DMAINMENL 128 This type of interface requires an action from the part of the user to indicate when it is finished modifying the name and desires to apply the changes Another possibility w
215. are there anyway Build huge tables of data Use virtual memory reserve contiguous address space etc Registry A global database for configuration options Services Run processes in the background without being bothered by a console window or any other visible interface Shell programming Manage files folders shortcuts and the desktop Terminal services Terminal Services provides functionality similar to a terminal based centralized host or mainframe environment in which multiple terminals connect to a host computer A user can log on at a terminal and then run applications on the host computer accessing files databases network resources and so on Each terminal session is independent with the host operating system managing conflicts between multiple users contending for shared resources Windows Yes Windows is about windows You get a huge variety of graphical objects from the simple check box to sophisticated tree displaying stuff An enormous variety of things that wait for you ready to be used 1 Media Control Interface 2 17 1 Clipboard The data in the clipboard is tagged with a specific format code To initiate the data transfer to or from the clipboard you use OpenClipboard GetClipboardData allows you to read it SetClipboardl Data to write it etc You implement this way the famous Cut Copy and Paste commands that are ubiquitous in most windows applicatio
216. arg2 We just return the difference between both numbers If arg is bigger than arg2 this will be a positive number if they are equal it will be zero and if arg is smaller than arg2 it will be a negative number just as qsort expects Right before we display the results then we add the famous call we have been working so hard to get to 61 The compiler emits a record for the linker telling it to put there the address of the global if the argument is a global variable or will emit the right instructions to access the address of a local using the frame pointer This has been working for a while now 104 C programming with Icc win32 qsort Frequencies 256 sizeof int compare We pass the Frequencies array its size the size of each element and our comparison function Here is the new version of our program for your convenience New code is in bold include lt stdio h gt include lt stdlib h gt int Frequencies 256 Array of frequencies int compare const void argl const void arg2 Compare both integers return int argl int arg2 int main int argc char argv int count 0 FILE infile int c if arge lt 2 infile fopen argv 1 rb if infile NULL c fgetc infile while c EOF fclose infile printf d chars in file n count qsort Frequencies 256 sizeof int compare for count 0 count lt 256 count
217. as a much more sophisticated help engine A more advanced window 261 The WinMain procedure is the right place for initializing other things like CoInitialize if you are going to use COM or WSAStartup if you are going to use the sockets layer etc The command line parameters are available in the lpCmdLine parameter The messages for the main window are handled in the MainWndProc function that is passed as the message handling function when registering the window class The standard version looks like this each event is mapped to a case in a big switch of possible events LRESULT CALLBACK MainWndProc HWND hwnd UINT msg WPARAM wParam LPARAM lParam switch msg case WM_SIZE Windows has been resized Resize any child windows here SendMessage hWndStatusbar msg wParam lParam InitializeStatusBar hWndStatusbar 1 break case WM_MENUSELECT The user is browsing the menu Here you can add code to display some text about the menu item being browsed for instance return MsgMenuSelect hwnd msg wParam lParam The WM_COMMAND message reports an item of the menu has been selected case WM_COMMAND HANDLE WM COMMAND hwnd wParam lParam MainWndProc_OnCommand break This message reports that the window will be destroyed Close the application now case WM_DESTROY PostQuitMessage 0 break All other messages go to the default procedure provided by Windows default return DefWindowProc hwnd msg wParam l
218. ase this fixed fields will be membbers of a larger structure and they will be always at the same position The controls that use this interface were introduced into windows later in 1995 than the first ones that were present in all the earlier versions of windows They are the following Control Notifications Animation control An animation control is a window that displays an Audio Video Interleaved AVI clip An AVI clip is a series of bitmap frames like a movie Animation controls can only display AVI clips that do not contain audio This control is currently not supported by the resource editor Date and time They allow the user to input a date or a time The notifications use picker controls the prefix DTN_XXX Header controls A header control is a window that is usually positioned above col umns of text or numbers It contains a title for each column and it can be divided into parts The user can drag the dividers that separate the parts to set the width of each column The notifications use the prefix HDN_XXX Not currently supported in the resource editor Hot key controls A hot key control is a window that enables the user to enter a combi nation of keystrokes to be used as a hot key A hot key is a key com bination that the user can press to perform an action quickly For example a user can create a hot key that activates a given window and brings it to the top of the z order The hot key control displays
219. at allows to compress and decompress data to save space It is writ ten by Jean Loup Gailly and Mark Adler 1 1 8 Structured Query Language SQL This is a database library based on the public domain sqlite package It is a very complete implementation of SQL with a good interface to the C language It comes with a documenta tion adapted to the windows environment accessible through the Icc win IDE 1 1 9 Safer C Library Microsoft proposed to replace many of the standard C functions with this library and pre sented a proposal to the C standards committee Even if it is not complete and the design is flawed it is a step in the right direction We show here an example of a library usage consult the documentation for a full description 1 1 10 The regular expressions library A grep clone A regular expression is a string that describes or matches a set of strings according to certain syntax rules Regular expressions are used by many text editors and utilities to search and manipulate bodies of text based on certain patterns The task at hand is then to build a program that will accept a regular expression pattern and a set of files in the form of a specification like c and will print in the standard output all lines that match the regular expression with their line number We have then two tasks 1 The first one is to find all files that match a possibly ambiguous file specification like for in
220. ath The code looks like this include lt windows h gt This function returns 1 if its argument is a directory zero otherwise static int IsDirectory char fname char tmpbuf MAX_PATH 2 p int a if fname memset tmpbuf 0 sizeof tmpbuf strncpy tmpbuf fname 1 strlen fname 2 p tmpbuf lse p fname a GetFileAttributes p if a gt 0 amp amp a amp FILE_ATTRIBUTE_DIRECTORY return 1 return 0 int AddToPath char newpath HKEY hkey int siz len unsigned long dwType dwReturnValue char p FAQ 369 char buf 8192 8K path length should suffice Open the environment block for the current if RegOpenKeyExA HKEY_CURRENT_USER Enviro KEY_QU T nment 0 RY_VALUE KEY_SET_VALUE amp hkey return ERROR_ACCESS_DENIED Query th value of the current path siz sizeof buf dwType REG_EXPAND_SZ if RegQueryValuel ERROR_SUCCESS We can t open this key probably because we have no to the environment or to the registry access T user ERROR_SUCCESS EXA hkey path 0 amp dwType buf amp siz return RegCloseKey hkey ERROR_ACCESS_DENIED Check for weird situations if siz lt 0 This could be the
221. athFromIDList ItemIDList result 12 if result 0 r 1 13 pMalloc gt lpVtbl gt Free pMalloc ItemIDList 14 pMalloc gt lpVtbl gt Release pMalloc 15 return Small isn t it Let s see the gory details We need a local variable that will hold a pointer to a shell defined function that will allocate and release memory The shell returns us a result that needs memory to exist We need to free that memory and we have to take care of using the same function that the shell uses to allocate memory This pointer to an interface the malloc interface will be in our local variable pMal loc The shell needs information about the environment and some pointers to put the results of the interaction with the user We will see more of this when we fill this structure below The shell uses a lot of stuff and we have to take care to avoid filling our brain with unending details What is an ITEMLIST Actually I haven t even bothered to read the docs about it since the only use I found is to pass it around to other shell functions The result of the function is initialized to zero i e we will set this result to 1 only and only if there is a valid path in the buffer OK Here we start The first thing to do then is to get the pointer to the shell allocator If any thing goes wrong there there is absolutely nothing we can do and the best thing is to return immediately with a FAL
222. ave a memory leak built in into our software A way out of this is very easy though We could just convert our mem structures into a linked list and free the memory at the end of the program 1 31 3 Displaying the results After all this work we have a program that will compile when run but is missing the essential part showing the results to the user Let s fix this We need to sort the words by frequency and display the results We build a table of pointers to word list structures and sort it But to know how big our table should be we need to know how many words we have entered This can be done in two ways Either count the number of words in the table when building the report or count the words as we enter them Obviously the second solution is simpler and requires much less effort We just declare a global integer variable that will hold the number of words entered into the table so far int words 0 We increment this counter when we enter a new word i e in the function NewWordList 77 We will need a comparison function for the qsort library function too int comparewords const void wl const void w2 WORDLIST pwl WORDLIST wl pw2 WORDLIST w2 76 Note that we allocate MEM_ALLOC_SIZE bytes If we want to change to more or less bytes we just change the define line and we are done with the change Counting words 157 if pwl gt Count pw2 gt Count return strcmp pwl g
223. ave this problem as an exercise to the reader 258 C Tutorial e Initialize the application register the window classes etc e Start the message pump e Process events until a predefined event generally the closing of the main window provokes the stop of the message pump e Cleanup This was the standard way of windows programming until the C wizards decided that this message pump was too ugly to be shown to programmers and hid it behind an application object Later several years later things changed again and the ATL environment made the famous message pump visible again 118 Texts started appearing explaining the surprised programmers what was WinMain and that message pump that was again the non plus ultra of modernity 9 Luckily for people pro gramming in C all those fads were invisible Since C programming emphasizes low level knowledge of what is going on the message pump has always been there and we knew about it Messages are sent to window objects that are members of a class of similar objects or window class The procedure SendMessage can also send messages to a window object as if they would have been sent by the system itself We send for instance the message EM_SETLIMITTEXT to an entry field to set the maximum number of characters that the entry field will process The system relies on the window procedure passing all messages that it doesn t handle to the default messag
224. bad pointer would not only destroy the data of the application where it belonged but destroyed data of other applications making the whole system unstable But this means too that applications can t share data by sending just pointers around A pointer is meaningful only in the application where it was created Special mechanisms are needed and provided by Windows to allow sharing of data between applications 75 This discussion is based upon the article of Randy Kath published in MSDN Memory management strategies 145 1 30 Memory management strategies Each program needs some workspace to work in How this space is managed allocated recy cled verified makes a memory allocation strategy Here is a short description of some of the most popular ones 1 30 1 Static buffers This is the simplest strategy You reserve a fixed memory area buffer at compile time and you use that space and not a byte more during the run time of the program Advantages 1 Itis the fastest possible memory management method since it has no run time overhead There is no memory allocation nor recycling that incurs in run time costs 2 In memory starved systems embedded systems micro controller applications etc it is good to know that there is no possibility of memory fragmentation or other memory space costs associated with dynamic allocation Drawbacks 1 Since the amount of memory allocated to the program is fixed it is not possible to
225. basic idea is to use a table of function pointers as a decision table This can be done like this include lt stdio h gt include lt stdlib h gt typedef void callback int void zero int void greaterZero int We define a table of two functions that represent a boolean decision Using function pointers 177 indexed by either zero or one callback callbackTable 2 zero greaterZero void zero int a exit EXIT_SUCCESS This terminates recursion void greaterZero int a printf d n a callbackTable a gt 0 a recurse with a 1 int main int argc char argv assume correct arguments n gt 0 greaterZero atoi argv 1 return 0 Error checking can be added to the above program in a similar way This is left as an exercise for the interested reader Of course the utility of function tables is not exhausted by this rather artificial example Deci sion tables can be used as a replacement of dense switch statements for instance When you are very interested in execution speed this is the fastest way of making multi way branches Instead of writing switch a case 1 some code break case 2 break you could index a table of functions each function containing the code of each case You would construct a function table similar to the one above and you would go to the correct case function using Table a The best is of co
226. before the dialog is visible in the screen Here is done the initialization of the dialog box data structures or other things The wizard inserts here a call to a procedure for handling this message 2 WM_COMMAND This message is sent when one of the controls or child windows if you want to be exact has something to notify to the dialog a button has been pressed a check box has been pressed data has been entered in an entry field etc Since we can have several controls we use again a switch statement to differentiate between them Switch statements can be nested of course 3 WM_CLOSE This message arrives when the user has pressed the close button in the system menu or has typed the Alt F4 keyboard shortcut to close the dialog Now the whole purpose of this exercise is to input a character string The text is entered by the user in our entry field It is important from a user s perspective that when the dialog box is displayed the cursor is at the beginning of the entry field It could be annoying to click each time in the entry field to start editing the text We take care of this by forcing the focus to the entry field Under windows there is always a single window that has the focus 1 e receives all the input from the keyboard and the mouse We can force a window to have the focus using the SetFo cus API static int InitializeApp HWND hDlg WPARAM wParam LPARAM lParam SetFocus GetDlgItem hDlg ID
227. ber is 123 45 and the imaginary part is 67 89 The con stant I represents 0 0 1 0i or csqrt 1 and is defined in complex h 208 C programming with Icc win32 1 1 The libraries of lcc win Lcc win comes with many useful libraries already compiled and ready to use Name include Binary lib file Regular expressions regexp h regexp lib Perl regular expressions pcre h pere lib Console routines tcconio h tcconio lib Statistics stats h stats lib SQL library sqlite3 h sqlite3 lib Linear algebra matrix h matrix lib Network utilities netutils h netutils lib Advanced math functions specialfns h libc lib Safer C library libc lib Zlib functions zlib h zlib lib 1 This library will be included automatically it is not necessary to add it at link time 1 1 1 The regular expressions libraries The C language started under the Unix operating system and that system provided since quite a long time a regular expressions library For reasons unknown to me that library wasn t included in the language Lcc win provides it with the implementation proposed by Henry Spencer from the university of Toronto Another regular expression package is the one compatible with the PERL language This library was written by Philippe Hazel from the University of Cambridge 1 1 2 Console formatting routines This library was developped by Daniel Guerrero Miralles and emulates the old Turbo C com piler func
228. beyond the end of the string you are modifying Some other compilers like gcc will store those strings in read memory marked as read only what will lead to an exception if you try to modify this Lcc win doesn t do this for different reasons but even if you do not get a trap it is a bad practice that should be avoided A common beginner error is char a hello char b world strcat a b In this case you are adding at the end of the space reserved for the character array hello another character string destroying whatever was stored after the a character array 220 C programming with Icc win32 1 3 12 Indefinite order of evaluation Consider this code fn pointer gt member pointer amp buffer 0 This will work for some compilers gcc lcc win and not for others The order of evaluation of arguments in a function call is undefined Keep this in mind If you use a compiler that will evaluate the arguments from left to right you will get a trap or a nonsense result 1 3 13 A local variable shadows a global one Suppose you have a global variable say buf If you declare a local variable of the same name at an inner scope the local variable will take precedence over the global one i e when you write unsigned char buf BUFSIZ int fn int a char buf 3 buf BUFSIZ 1 0 Error the local variable is accessed not the global one Giving the command line option shadows to
229. bit Leave set to 0 83 http msdn microsoft com library default asp url library en us vccore98 html core_raising software_exceptions asp Advanced C programming with Icc win 185 You can set the first two bits to a setting other than 11 binary if you want although the error setting is appropriate for most exceptions The important thing to remember is to set bits 29 and 28 as shown in the previous table End quote Note that nowhere will be said that the actual code will be changed by the operating system Just recommendations But anyway Follow this schema and you may be happy with it 1 36 5 4 Giving more information A 32 bit integer can be too little data for describing what happened Additional data can be channeled through the exception arguments using the RaiseException API You can pass up to 15 arguments when you raise an exception For instance here we will pass the name of the function that provoked the error in the first parameter include lt stdio h gt include lt seh h gt int fn void unsigned argstable 1 argstable 0 unsigned func_ RaiseException 0xe0000001 0 1 argstable return 0 Not reached int main void unsigned code __try fn _ except code GetExceptionCode EXCEPTION_EXECUTE_HANDLER EXCEPTION_POINTERS ex GetExceptionInformation printf Error code x n code printf In function s n char ex gt
230. bitrarily small value when the program is first loaded just 4096 bytes 1 page The stack then grows on demand to meet the needs of the thread This is implemented by plac ing a page with PAGE_GUARD access at the end of the current stack When your code causes the stack pointer to point to an address on this page an exception occurs The system then does the three following things 1 Remove the PAGE_GUARD protection on the guard page so that the thread can read and write data to the memory 2 Allocate a new guard page that is located one page below the last one 3 Rerun the instruction that raised the exception If a thread in your program grows the stack beyond its limit 1MB with normal programs the step 1 above will succeed but the step 2 will fail The system generates an exception and the first try block is executed This is OK but the stack has been left without a guard page Since the second time that we get a stack overflow there is no more stack left the program will pro voke an access violation when it attempts to use the stack within the code of the exception handling procedure __except_handler3 that receives the exception from windows This will provoke the dreaded double fault exception that terminates immediately the program no ques tions asked Note that not even the this program has attempted an illegal operation dialog box appears The correct way of handling stack overfl
231. ble amp msg TranslateMessage amp msqg DispatchMessage amp msqg Returns the wParam of the WM_QUIT message return msg wParam We have the same schema that we saw before but this time with some variations We start the application registering the window class etc we load the keyboard accelerators we create the window the status bar we show our window and then we enter the message loop until we receive a WM_QUIT that breaks it We return the value of the wParam parameter of the last message received WM_QUIT of course Simple isn t it Now let s look at it in more detail The InitApplication procedure initializes the WNDCLASS structure with a little more care now since we are not using our DefDialogProc any more there are a lot of things we have to do ourselves Mostly that procedure uses the standard settings static BOOL InitApplication void WNDCLASS wc memset amp wc 0 sizeof WNDCLASS The window style we style CS_HREDRAW CS_VREDRAW CS_DBLCLKS we lpfnWndProc WNDPROC MainWndProc 260 C Tutorial wc hInstance hInst The color of the background we hbrBackground HBRUSH COLOR_WINDOW 1 we lpszClassName winexampleWndClass The menu for this class wc lpszMenuName MAKEINTRESOURCE IDMAINMENU default cursor shape an arrow we hCursor LoadCursor NULL IDC_ARROW defau
232. bout WinMain and that statement LoadAccelerators Well let s go back to that piece of code again After loading the accelerators the status bar is created at the bottom of the window and then at last we show the window Note that the window is initially hidden and it will be shown only when all things have been created and are ready to be shown This avoids screen flicker ing and saves execution time It would be wasteful to redraw the window before we created the status bar since we would have to do that again after it is created We will speak about status bar later since that is not crucial now What really is important is the message loop that begins right after we call Show Window whil GetMessage amp msg NULL 0 0 if TranslateAccelerator msg hwnd hAccelTable amp msg TranslateMessage amp msqg DispatchMessage amp msqg This loop calls the API GetMessage If that returns TRUE we call the API to translate the accelerators This API will convert a sequence of keystrokes into a WM_COMMAND mes sage as it was sent by a menu if it finds a correspondence between the keystrokes and the accelerator table that we loaded just a few lines above If TranslateAccelerator doesn t find any correspondence we go on by calling TranslateMessage that looks for sequences of key pressing and key up messages and does the dirty work of debouncing the keyboard handling repeat sequences etc At last we dispatch our
233. can be either zero or one char 1 Character or small integer type Comes in two fla vours signed or unsigned short 2 Integer or unicode character stored in 16 bits Signed or unsigned int 4 Integer stored in 32 bits Signed or unsigned long 4 Identical to int In lcc win64 this is 32 bits too In Linux 64 bits versions it is 64 bits pointer 4 All pointers are the same size in Icc win long long 8 Integer stored in 64 bits Signed or unsigned float 4 Floating point single precision Approx 7 digits double 8 Floating point double precision Approx 15 digits long double 12 Floating point extended precision Approx 19 digits float _Complex 32 Complex numbers Each _Complex is composed of double _Complex 32 two parts real and imaginary part Each of those long double _Complex 32 parts is a floating point number Include lt complex h gt when using them 1 The actual type of the Boolean type should be bool but in the standard it was specified that this type wouldn t be made the standard name for now for compatibility reasons with already running code If you want to use bool you should include the header stdbool h These are the basic types of ANSI C Lcc win offers you other types of numbers To use them you should include the corresponding header file they are not built in into the compiler They are built using a property of this compiler that allows you to define your own kind of Type Head
234. case DLL PROCESS_DETACH UnregisterClass dialog hDLLInst break case DLL THREAD ATTACH break case DLL THREAD DETACH break return TRUE This function like our dialog function or many other functions under windows is a callback function i e a function that is called by the operating system not directly from our code Because of this fact its interface the arguments it receives and the result it returns is fixed The operating system will always pass the predefined arguments to it and expect a well defined result The arguments that we receive are the following 1 We receive a HANDLE to the instance of the DLL Note that we have to pass to several functions this handle later on so we will store it away in a global variable 2 We receive a DWORD an unsigned long that contains a numerical code telling us the reason why we are being called Each code means a different situation in the life cycle of the DLL We have a code telling us that the we were just loaded DLL_PROCESS_ATTACH another to inform us that we are going to be unloaded DLL_PROCESS_DETACH another to inform us that a new thread of execution has been started DLL_THREAD_ATTACH and another to tell us that a thread has finished DLL_THREAD_DETACH 3 The third argument is reserved by the system for future use It is always zero The result of LibMain should be either TRUE the DLL has been correctl
235. case when the PATH RegCloseKey hkey return ERROR_BAD_ENVIRONMENT Verify that the argument is a directory if IsDirectory newpath RegCloseKey hkey return ERROR_BAD_PATHNAM Gl is just not set Check that this entry is not already in the Path If the argument is enclosed by or Tel EOS OR is at the beginning of the path string return zero no problems p buf do p stristr p newpath if p char q p 1 char pEnd p strlen newpath but do not add the entry a second time If newpath is exactly the first entry q points to invalid memory Check for the case wher if p buf amp amp q amp amp pEnd 0 p RegCloseKey hkey return 0 else if p buf amp amp pEnd p buf 370 C Tutorial RegCloseKey hkey return 0 else ptt while p If needed add a before adding the new entry if buf siz 1 amp amp newpath 0 if siz lt sizeof buf 1 Streat buf siztt else RegCloseKey hkey return ERROR_NOT_ENOUGH_MEMORY len strlen newpath Check that our buffer will not overflow if len siz gt sizeof buf RegCloseKey hkey return HRROR_NOT_ENOUGH_MEMORY strcat buf newpath siz strlen buf if Reg
236. cases even when all of the items of the list box are visible and some white space is left at the bot tom The basic idea is to subtract each line height from the total height of the client area of the list box int ntop nCount nRectheight nVisiblelItems RECT re itemrect First get the index of the first visible item ntop SendMessage hwndList LB_GETTOPINDEX 0 0 Then get the number of items in the list box nCount SendMessage hwndList LB_GETCOUNT 0 0 Get the list box rectangle GetClientRect hwndList amp rc Get the height of the list box s client area nRectheight rec bottom rc top This counter will hold the number of visible items nVisibleItems 0 Loop until the bottom of the list box or the last item has been reached Some Coding Tips 341 while nRectheight gt 0 amp amp ntop lt nCount Get current line s rectangle SendMessage hwndList LB_GETITEMRECT ntop DWORD amp itemrect Subtract the current line height nRectheight nRectheight itemrect bottom itemrect top nVisibleItemst Increase item count Ntopt Move to the next line 2 21 10 Starting a non modal dialog box Non modal dialog boxes behave as independent top level windows They can be started using the CreateDialog function HWND CreateDialog HINSTANCE hInstance handle to application instance LPCTSTR lpTemplate Ident
237. ccess the members of an unnamed union structure without having to write t u sign t u e etc 200 C programming with Icc win32 number t t f 1 178 125 pfloat t return 0 This will produce the output Sign 0 exponent 134 127 7 fraction 01100100010000000000000 To calculate the fraction we do fraction 01100100001 1 2 1 4 1 8 1 16 1 32 1 64 t 1 1 1024 rFOoOOrRRO F F OF This is 0 25 0 125 0 015625 0 0009765625 0 3916015625 Then we add 1 to 0 3916015625 obtaining 1 3916015625 This number we multiply it by 2 7 128 1 3916015625 128 178 125 1 37 2 4 Rounding modes When the result of a computation does not hit directly a number in our representation grid we have to decide which number in the grid we should use as the result This is called rounding We have the following rounding modes 1 Round to the nearest grid point This is the default setting when a program compiled with Icc win starts executing 2 Round upwards Choose always the next higher grid point in the direction of positive infinity 3 Round downwards Choose always the next lower grid point in the direction of negative infinity 4 Round to zero We choose always the next grid point in the direction of zero If the number is positive we round down if it is negative we round up This rounding modes are defined in the standard header file fenv h as Rounding direction macros
238. ce files generated by the resource compiler are passed to the linker that con verts them into resource specifications to be included in the executable Note that actually you do not need to know this language because the IDE has a resource edi tor that can be used to build graphically using drag and drop the dialog box But the emphasis here is to introduce you to the system so that you know not only what button should you push but why you should push that button too But we wanted originally to make a dialog box containing an edit field We are far away from our objective yet Introduction to windows programming 235 We come back to Wedit after closing our text file dialog rc and we go to the Design menu bar and press Open new 105The resource editor opens up and we see the following display has wedit listbox resource listbox _ 5 x le x Text Diao Tie Dialog 1000 z Ty co FF 3 ii ae El EM ES Oo E Dialog Title Near the top left border you see a button like this If you click in that button the controls palette opens 105 Why should introductory texts be clear Why not make obfuscated sentences There is even an obfuscated C contest Who writes the most incomprehensible program Quite a challenge With the documentation you can do even better you write docs that are so incomprehensible that nobody reads them 236 C Tutorial Controls palette Controls
239. ceive data Send and receive data Disconnect Disconnect 3 7 1 Common steps for server and client 3 7 1 1 Initializing All Winsock applications must be initialized to ensure that Windows sockets are supported on the system To initialize Winsock you should call the WSAStartup function giving it the ver sion number you want to use and the address of a WSADATA structure where windows writes information about the type of network software that is running A typicall call would be WSADATA wsadata if WSAStartup MAKEWORD 2 1 amp wsaData 0 return GetLastError The cryptic MAKEWORD 2 1 means we want at least version 2 1 of the network software Note that the library included with Icc win doesn t need this step since it will perform it auto matically if it detects that the network wasn t initialized 3 7 1 2 Creating a socket Once initilized we can create a socket trough which we are going to send and receive the data We call for this the socket function SOCKET Socket socket AF_INET SOCK_STREAM IPPROTO_TCP The error report of the socket call is a return value of INVALID_SOCKET A typical sequence would be if Socket INVALID_SOCKET Client Server programming using sockets 401 printf Error ld n WSAGetLastError Note that under the UNIX operating system socket descriptors are equivalent to file handles This is
240. ch and some buttons to indicating case sensitivity etc We close the menu editor and we start a new dialog 129 A debugger is a program that starts another program the program to be debugged or debuggee and can execute it under the control of the user that directs the controlled execution All C development systems offer some debugger and Icc win is no exception The debugger is described in more detail in the user s manual and it will not be described here Suffice to note that you start it with F5 or Debugger in the compiler menu you can single step at the same level with F4 and trace with F8 The debugger shows you in yellow the line the program will execute next and marks breakpoints with a special symbol at the left Other debuggers may differ from this of course but the basic operations of all of them are quite similar Note that Icc win is binary compatible with the debugger of Microsoft you can debug your programs using that debugger too To be able to use the debugger you need to compile with the g2 flag on That flag is normally set by default It directs the compiler to generate information for the debugger to enable it to show source lines and variable values The compiler generates a whole description of each module and the structures it uses called debug information This information is processed by the linker and written to the executable file If you turn the debugging flag off the debugger will not
241. ch an option is falling into the featurism that pervades all modern software Learn when to stop 1 18 Using arrays and sorting Suppose we want to display the frequencies of each letter in a given file We want to know the number of a s of b and so on One way to do this is to make an array of 256 integers one integer for each of the 256 possible character values and increment the array using each character as an index into it When we see a b we get the value of the letter and use that value to increment the corresponding posi tion in the array We can use the same skeleton of the program that we have just built for counting characters modifying it slightly gt include lt stdio h gt include lt stdlib h gt int Frequencies 256 Array of frequencies int main int argc char argv Local variables declarations int count 0 FILE infile int c if arge lt 2 56 Yes code reuse is not only possible in object oriented programming 98 C programming with Icc win32 printf Usage countchars lt file name gt n exit EXIT_FAILURE infile fopen argv 1 rb if infile NULL printf File s doesn t exist n argv 1 exit EXIT_FAILURE c fgetc infile while c EOF count Frequencies c c fgetc infile fclose infile printf d chars in file n count for count 0 count lt 256 count if Frequencies count 0 printf
242. clares a reference to the integer a Here we have an integer that within this scope will be called a Its machine address will be stored in a pointer to this integer called pa This pointer will be able to access the data of a i e the value stored at that machine address by using the operator When we want to access that data we write pa 8944 This means store at the address contained in this pointer pa the value 8944 We can also write int m 698 pa This means add to 698 the contents of the integer whose machine address is contained in the pointer pa and store the result of the addition in the integer m We have a reference to a that in this scope will be called ra Any access to this compiler maintained pointer is done as we would access the object itself no special syntax is needed For instance we can write ra rat78 79 Note that with references the operator is not needed The compiler will do automatically this for you It is obvious that a question arises now why do we need references Why can t we just use the objects themselves Why is all this pointer stuff necessary Well this is a very good question Many languages seem to do quite well without ever using pointers the way C does The main reason for these constructs is efficiency Imagine you have a huge database table and you want to pass it to a routine that will extract some information
243. colon at the end 1 if value gt MAXVAL break The compiler will report an error The problem is easily spotted when the macro substitution is performed on the above line Using the definition for MAXVAL the substituted version reads if value gt 10 break The semi colon in the definition was not treated as an end of statement indicator as expected but was included in the definition of the macro MAXVAL The substitution then results in a semi colon being placed in the middle of the controlling expression which yields the syntax error Remember the pre processor does only a textual substitution of macros 1 3 8 Watch those semicolons Yes speaking about semicolons look at this if x j gt 25 x j 25 The semicolon after the condition of the if statement is considered an empty statement It changes the whole meaning of the code to this if x j gt 25 x j 25 The x j 25 statement will be always executed 1 3 9 Assuming pointer size is equal to integer size Today under Icc win the sizeof void is equal to the sizeof int This is a situation that will change in the future when we start using the 64 bit machines where int can be 32 bits but Pitfalls of the C language 219 pointers would be 64 bits This assumption is deeply rooted in many places even under the windows API and it will cause problems in the future Never assume that a pointer is going to fit in an integer if po
244. contains the case for all other values that do not appear explicitly in the switch It is a good practice to always add this keyword to all switch state ments and figure out what to do when the input doesn t match any of the expected values If the input value doesn t match any of the enumerated cases and there is no default statement no code will be executed and execution continues after the switch Conceptually the switch statement above is equivalent to if pet CAT printf This is a cat else if pet DOG printf This is a dog else if pet MOUSE printf This is a mouse else printf Unknown animal Both forms are exactly equivalent but there are subtle differences Switch expressions must be of integer type The if form doesn t have this limitation In the case of a sizeable number of cases the compiler will optimize the search in a switch statement to avoid comparisons This can be quite difficult to do manually with if s Cases of type other than int or ranges of values can t be specified with the switch statement contrary to other languages like Pascal that allows a range here Switch statements can be nested to any level i e you can write a whole switch within a case statement but this makes the code unreadable and is not recommended 1 13 28 Inline This instructs the compiler to replicate the body of a function at each call site For instance int inline f int a
245. cording to the specifi cations it finds in the executable file The dialog box procedure is the parent window of all the controls that appear in it When an event happens that possible needs that the control notifies the application about it the control sends a notification message For instance when the user types a character into an edit field the edit control sends a notification to the parent window specifying the character received Notifications can be sent in the form of a WM_COMMAND message or in the form of a WM_NOTIFY message Window controls 269 The following controls send a WM_COMMAND message to notify the parent window of an event Control Notifications Button Notifies the parent window when it has been selected See the doc umentation for the BN_XXX messages Combobox These controls are a combination of a list box and an edit field so the notifications it sends are a combination of both See the docu mentation for CBN_XXX messages Edit These controls are used for text input They notify the parent when a character has been received or in general when the text has been modified See the EN_XXX messages Listbox These controls display a variable length list They notify the parent window when an item has been selected or clicked Scrollbar These controls let the user choose the amount of scrolling that should be done for the information being displayed They notify the parent window when the
246. cro name gt command This is useful for avoiding name clashes Remember that when you define a macro the name of the macro will take precedence before everything else since the compiler will not even see the identifier that holds the macro This can be the origin of strange bugs like int fn int a some code If you have the idea of defining a macro like this define fn 7987 the definition above will be transformed in int 7987 int a A closer look at the pre processor 171 not exactly what you would expect This can be avoided by undefining the macros that you fear could clash with other identifiers in the program 1 34 1 2 Conditional compilation Very often we need to write some kind of code in a special situation and some other kind in another situation For instance we would like to call the function initUnix when we are in a UNIX environment and do NOT call that function when in other environments Besides we would like to erase all UNIX related instructions when compiling for a windows platform and all windows related stuff when compiling for Unix This is achieved with the preprocessor ifdef UNIX lines for the Unix system else lines for other non unix systems endif This means If the preprocessor symbol UNIX is defined include the first set of lines else include the second set of lines There are more sophisticated usages with the elif directive ifdef UNIX Unix st
247. ct 23 FillRect nDC amp m_rect hbBkBrush 24 x y 0 25 for int ix 0 ix lt len ix 26 GetCharBmpOffset amp rc char Text ix CharacterWidth 27 CharacterXSpacing CharacterHeight CharacterYSpacing 28 BitBlt hDC x y CharacterWidth CharacterXSpacing 29 CharacterHeight CharacterYSpacing dcMemory rc left 30 rc top SRCCOPY 31 x CharacterWidth CharacterXSpacing 32 charcount 33 if charcount MaxXCharacters amp amp MaxYCharacters 1 34 break 39 else if charcount MaxXCharacters amp amp MaxYCharacters gt 1 36 37 if linecount MaxYCharacters 38 break 39 x charcount 0 40 y CharacterHeight CharacterYSpacing 41 linecount 134 The exact values are RGB 63 181 255 RGB 23 64 103 and RGB 0 0 0 Building custom controls 307 EndPaint hwnd amp ps SelectObject dcMemory oldBitmap DeleteDC dcMemory DeleteObject bmp DeleteObject hbBkBrush OAarATNA ON FWD ey DB DB DB DB YB WW The first thing our procedure does is to obtain a device context from Windows 2 This device context is already clipped to the area we should draw We suppose that the text of the Icd is stored in the variable Text and we get its length 3 To make the translation from the colors in the bitmap to the colors of our lcd window we use the primitive CreateMappedBitmap that translates a bitmap with a set of source color
248. ctangular windows In previous versions of Windows and Windows NT it was possible to create only rectangular windows To simulate a non rectangular window required a lot of work on the application developer s part Besides handling all drawing for the window the application was required to perform hit testing and force underlying windows to repaint as necessary to refresh the trans parent portions of the window Windows 95 and Windows NT version 3 51 greatly simplify this by providing the SetWin dowRgn function An application can now create a region with any desired shape and use Set WindowRgn to set this as the clipping region for the window Subsequent painting and mouse messages are limited to this region and Windows automatically updates underlying windows that show through the non rectangular window The application need only paint the window as desired For more information on using SetWindowRgn see the Win32 API documentation 2 22 11 How dol implement a non blinking caret Although Windows is designed to blink the caret at a specified interval a timer function and SetCaretBlinkTime can be used to prevent Windows from turning the caret off by following these three steps e Call SetCaretBlinkTime 10000 which instructs Windows to blink the caret every 10 000 milliseconds 10 seconds This results in a round trip time of 20 seconds to go from OFF to ON and back to OFF or vice versa e Create a timer using SetTimer
249. ction if that function expects a reference and you pass it a reference the compiler will arrange for you passing only the address of the data pointed to by the reference 110 C programming with Icc win32 1 20 Structures and unions 1 20 1 Structures Structures are a contiguous piece of storage that contains several simple types grouped as a single object For instance if we want to handle the two integer positions defined for each pixel in the screen we could define the following structure struct coordinates int x int y Structures are introduced with the keyword struct followed by their name Then we open a scope with the curly braces and enumerate the fields that form the structure Fields are declared as all other declarations are done Note that a structure declaration is just that a dec laration and it reserves no actual storage anywhere After declaring a structure we can use this new type to declare variables or other objects of this type struct coordinate Coords 23 78 Here we have declared a variable called Coords that is a structure of type coordinate i e hav ing two fields of integer type called x and y In the same statement we initialize the struc ture to a concrete point the point 23 78 The compiler when processing this declaration will assign to the first field the first number i e to the field x will be assigned the value 23 and to the field y will be assig
250. ction state HWND hwndItem Window handle of the control RECT rcItem Rectangle where we should do our drawing unsigned long itemData Specifies the application defined value associated with the menu item Customizing controls 303 Member Description be a combination of the following values ODS_CHECKED This bit is used only in a menu of an owner drawn combo box ODS_DEFAULT The item is the default item ODS_FOCUS The item has the keyboard focus ODS_GRAYED This bit is used only in a menu be highlighted when the mouse is on the item the menu is inactive tor cues cues ODS_SELECTED The menu item s status is selected unsigned int itemState State of the item after the current drawing action takes place This can ODS_COMBOBOXEDIT The drawing takes place in the edit control ODS_DISABLED The item is to be drawn as disabled ODS_HOTLIGHT The item is being hot tracked that is the item will ODS_INACTIVE The item is inactive and the window associated with ODS_NOACCEL The control is drawn without the keyboard accelera ODS_NOFOCUSRECT The control is drawn without focus indicator With all this information we can do whatever we want inside the rcItem rectangle Here is the example for our problem of drawing a bitmap in each line of the combo box First in our dialog procedure we handle the message WM_DRAWITEM of course BOOL WINAPI MyDlgProc HWND hwnd UINT msg WPARAM
251. cular user The GetWindowsDirectory API has to do a lot more stuff including allocating memory for buffers And that allocation can fail and the devel oper at Microsoft did the right thing and tested if that memory allocation call worked or not and if not it returns an error failure Besides that API will work now but who knows what the future versions of windows will do Why leave a possible bug in there But this is difficult to do Checking the return value of ALL API calls is feasible but is very complex and time consuming And as everyone knows it is not a matter of the developer only How big is the time budget allocated to you for developing this application How much effort should be spent in making this application 100 bullet proof Those questions should be answered but they are not only the responsibility of the developer 2 19 2 Always check allocations Even in this days of 512MB RAM being common configurations and with swap files extend ing into the gigabyte memory failures can happen Specially in the case of infinite loops where all bets are off and any memory allocation will fail And here the memory manager of Icc win will not help since it will return NULL also it can t do anything else Allocations can fail because of corrupted input data to the memory allocation function Sup pose this code int allocsiz buffer GC_malloc allocsiz If for any reason allocsiz goes negative GC_malloc will receive a negati
252. d return absname MAMA Get current directory For some reason unknown to mankind getcwd returns C FOO no at end if dir is NOT root yet it returns C with if cwd is root Go figure To make the result consistent for appending a file name GetCurrentDir adds the missing if needed Result always has final MT char GetCurrentDir void static char dir MAX_PATH getcwd dir sizeof dir Append if needed int lastchar strlen dir 1 if lastchar gt 0 amp amp dir lastchar if last char isn t strcat dir add one return dir 111 1 11 111 1 111111 Get user confirmation to recycle delete a file 1 111111111111111 BOOL confirm LPCTSTR pFileName while TRUE printf Recycle s Y N A11 pFileName char c getch if c printf C n exit 0 printf n switch tolower c case a bPrompt FALSE fall through case y return TRUE case n return FALSE 1 1 11 11 11 11 11 1 1 11 Get Windows system error message 1 1 11 11 11 1 11 1 1 11 LPCTSTR GetErrorMsg int err static char buf BUFSIZ 378 C Tutorial buf 0 0 Only Windows could have a function this confusing to get a simple error message E_ FROM _SYSTEM FormatMessage FORMAT_MESSAGI FORMAT _ MESSAGE _ IGNORE_INSERTS NULL
253. d that prints the number Advanced C programming with Icc win 179 1 36 Advanced C programming with Icc win Lcc win offers several extensions to the C language described below This extensions are not part of the C standard but they are very much like similar features of the C language so they should be able to run in other environments as well 1 36 1 Operator overloading When you write int a 6 b 8 int c atb you are actually calling a specific intrinsic routine of the compiler to perform the addition of two integers Conceptually it is like if you were doing int a 6 b 8 int c operator a b This operator function is inlined by the compiler The compiler knows about this operation and several others and generates the necessary assembly instructions to perform it at run time Lcc win allows you to define functions written by you to take the place of the built in opera tors For instance you can define a structure complex to store complex numbers Lcc win allows you to write COMPLEX operator COMPLEX A COMPLEX B Code for complex number addition goes here This means that whenever the compiler sees a b and a is a COMPLEX and b is a COM PLEX it will generate a call to the previously defined overloaded operator instead of com plaining about a syntax error This is called in tech speak operator overloading There are several rules for writing those functions
254. d destination files and do the file copy To minimize the amount of memory consumed for large files and make it possible to copy files that couldn t be mapped into our virtual address space entirely those over 2GB we limit the source and destination views to the smaller of the file size or a specified maximum view size MAX_VIEW_SIZE which is 96K If the size of file is smaller than the max view size we ll just map and copy it Otherwise we ll map a portion of the file copy it then map the next portion copy it etc until the entire file is copied MAP_SIZE is 32 bits because MapViewOfFile requires a 32 bit value for the size of the view This makes sense because a Win32 process s address space is 4GB of which only 2GB 2431 bytes may be used by the process However for the sake of making 64 bit arithmetic work below for file offsets we need to make sure that all 64 bits of limpest are initialized correctly a liBytesRemaining QuadPart liSrcFileSize QuadPart This assignment sets all 64 bits to this value liMapSize QuadPart MAX_VIEW_SIZE do Now we start our copying loop The min macro returns the smaller of two numbers liMapSize QuadPart min liBytesRemaining QuadPart liMapSize QuadPart liOffset QuadPart 1iSrcFileSize QuadPart liBytesRemaining QuadPart pSre BYTE MapViewOfFile hSrcMap FILE _MAP_READ 1i0ffset HighPart 1ioOffset LowPart liMapSize LowPart pDst BYTE MapViewOfF
255. d to find information about it When you start it for the first time it will display a blank window expecting that you tell it what it should do The first thing to do is to go to the File menu and select the New gt File item This will indi cate to the IDE that you want to start a new program module You get prompted with a small window that asks for the file name Just enter hello c You will see than that a blank sheet of fas wedit hello i temp hello c eee fol xi 3 File Edit Search Project Design Compiler Utils Yersions Window Help 18 x include lt stdio h gt int main void printf hello n return 0 hello exe built successfully 0 3 sec E build search paper opens where you can enter the text of the program You should type the program as shown and pay attention to avoid any typing mistake Remember the machine doesn t under stand anything If you forget a quote or any special sign it will not work and the compiler will spit error messages that can be confusing Check that you type exactly what you see above Once this is done you can compile and link edit your program by just clicking in the compile menu or pressing F9 14 To run the program you use the execute option in the Compiler menu or you type Ctrl F5 or you open a command shell and type the program s name Let s do it the hard way first The first thing we need to know is the name of the program
256. d to the executable and loaded by the system from there automat ically when using the DialogBox primitive Among other things then that procedure needs to know which dialog template should load to interpret it and it is this parameter that we pass with the MAKEINTRESOURCE macro Ok that handles at least I hope the second parameter of the DialogBox API Let s go on because there are still two parameters to go The third one is NULL Actually it should be the parent window of this dialog box Normally dialog boxes are written within an application and they have here the window handle of their parent window But we are building a stand alone dialog box so we left this parameter empty i e we pass NULL The last parameter is the DialogFunc function that is defined several lines below The DefDl gProc needs a procedure to call when something important happens in the dialog box a button has been pushed an edit field receives input etc Ok this closes the call of the DialogBox API and we are done with WinMain It will return the result of the DialogBox function We will see later how to set that result within our Dialog box procedure 2 1 2 Resources We mentioned before that there is a compiler for a small resource language that describes our dialog boxes Let s look at that with a little bit more detail before we go to our dialog proce dure Open that file that should be called dialog rc if you gave the project the
257. d window is received the parameters are passed to a macro defined in windowsx h that breaks up the wParam and lParam parameters into their respective parts and passes those to the MainWndProc_OnCommand function When this window is destroyed we post the quit message The function for handling the commands looks like this void MainWndProc_OnCommand HWND hwnd int id HWND hwndcCtl UINT codeNotify switch id TODO Add new menu commands here case IDM_EXIT PostMessage hwnd WM_CLOSE 0 0 break We find a comment as to where we should add our new command We gave our menu item Search the symbolic ID of IDM_SEARCH We modify this procedure like this void MainWndProc_OnCommand HWND hwnd int id HWND hwndCtl UINT codeNotify switch id TODO Add new menu commands here case IDM_SEARCH char text 1024 if CallDialog IDD_SEARCH SearchDlgProc LPARAM text DoSearchText text Filling the blanks 291 break case IDM_EXIT PostMessage hwnd WM_CLOSE 0 0 break When we receive the menu message then we call our dialog Since probably we will make several dialogs in our text editor it is better to encapsulate the difficulties of calling it within an own procedure CallDialog This procedure receives the numeric identifier of the dialog resource the function that will handle the messages for the dialog and an extra parameter for the dialog where
258. dProc and we add the WM_CREATE case to the switch of messages LRESULT CALLBACK MainWndProc HWND hwnd UINT msg WPARAM wParam LPARAM lParam static HWND hwndTree switch msg case WM_CREATE hwndTr CreateTr hwnd IDTREEWINDOW break This is top down design We hide the details of the tree window creation in a function that returns the window handle of the tree control We save that handle in a static variable We declare it as static so that we can retrieve its value at any call of MainWndProc 6 Our CreateTree function looks like this static HWND _stdcall CreateTree HWND hWnd int ID return CreateWindowEx WS_EX_CLIENTEDGE WC_TREEVIEW WS_VISIBLE WS_CHILD WS_BORDER TVS_HASLINES TVS_HASBUTTONS TVS_DISABLEDRAGDROP 0 0 0 0 hWnd HMENU ID hInst NULL This function receives a handle to the parent window and the numeric ID that the tree control should have We call the window creation procedure with a series of parameters that are well described in the documentation We use the value of the hInst global as the instance since the code generated by Wedit conveniently leaves that variable as a program global for us to use Note that we give the initial dimensions of the control as zero width and zero height This is not so catastrophic as it seems since we are relying in the fact that after the creation
259. dard handles of the child console based process HANDLE hStdInput Standard input handle of the child process HANDLE hStdOutput Standard output handle of the child process 366 C Tutorial HANDLE hStdError Standard error handle of the child process You can set these handles to either a pipe handle file handle or any handle that can do syn chronous reads and writes through the ReadFile and WriteFile API The handles must be inheritable and the CreateProcess API must specify that inheritable handles are to be inher ited by the child process by specifying TRUE in the bInheritHandles parameter If the parent process only wishes to redirect one or two standard handles specifying GetStdHandle for the specific handles causes the child to create the standard handle as it normally would without redirection For example if the parent process only needs to redirect the standard output and error of the child process then the hStdInput member of the STARTUPINFO structure is filled as follows hStdInput GetStdHandle STD_INPUT_HANDLE pana NOTE Child processes that use such C run time functions as printf and fprintf can behave poorly when redirected The C run time functions maintain separate IO buffers When redi rected these buffers might not be flushed immediately after each IO call As a result the out put to the redirection pipe of a printf call or the input from a getch call is not flushed immediately and delays
260. ddress We can print it out Consider this simple program 1 include lt stdio h gt 2 include lt stdbool h gt 3 define MAXNAME 128 4 struct person 5 char Name MAXNAME 6 int Age 7 bool Sex 8 double Weight 9 10 struct person Joe 11 int main void 12 13 printf Ox x d n amp Joe sizeof struct person 14 The address of operator in line 13 returns the index of the memory location where the Joe structure starts In my machine this prints 0x402004 144 The memory location 0x402004 4 202 500 in decimal contains the start of this data that goes up to 0x402094 4 202 644 When we write a function that should work with the data stored in that structure we give it just the number 4 202 500 That means The data starts at 4 202 500 No copying needed very efficient A pointer then is a number that contains the machine address i e the number of the memory location where the data starts The integer that contains a memory location is not necessarily the same as a normal int that can be smaller or bigger than an address In 64 bit systems for instance addresses can be 64 bits wide but int can remain at 32 bits In other systems Win 32 for instance a pointer fits in an integer 48 In some systems memory is not linear it is distributed in several areas that are in completely different places in the total addressing space In those systems an address is mor
261. di son Wesley For an example of network functions see Retrieving a file from the internet page 328 2 17 11 Hooks A hook is a mechanism by which a function can intercept events messages mouse actions keystrokes before they reach an application The function can act on events and in some cases modify or discard them This filter functions receive events for example a filter func tion might want to receive all keyboard or mouse events For Windows to call a filter function 320 C Tutorial the filter function must be installed that is attached to an entry point into the operating system a hook for example to a keyboard hook If a hook has more than one filter function attached Windows maintains a chain of those so several applications can maintain several hooks simultaneously each passing or not its result to the others in the chain 2 17 12 Shell Programming Windows provides users with access to a wide variety of objects necessary for running appli cations and managing the operating system The most numerous and familiar of these objects are the folders and files but there are also a number of virtual objects that allow the user to do tasks such as sending files to remote printers or accessing the Recycle Bin The shell organizes these objects into a hierarchical name space and provides users and applications with a con sistent and efficient way to access and manage objects 2 17 13 Services A service app
262. din stdout and stderr 2 Convert the FILE pointer into an operating system handle 3 Build a mapped view of the file using Map ViewOfFile 4 Use the GetMappedFileName API to retrieve the name This is the heart of the procedure 5 Translate file names that start with device HarddiskVolume 7 for instance into more user friendly names like D lude lt stdio h gt lude lt windows h gt incl incl incl lude lt psapi h gt int getfilename FILE f char buf size_t buflen void h m char p pfile int result 0 Step 1 Handle the trivial cases if f stdin strncpy buf stdin buflen result 5 else if f stdout strncpy buf stdout buflen result 6 else if f stderr strncpy buf stderr buflen result 6 else Step 2 Convert the FILE pointer into an operating system handle h void _get_osfhandle fileno f Step 3 Create a mapped view of the file m CreateFileMapping h NULL PAGE_READONLY 0 0 NULL if m INVALID HANDLE VALUE pfile MapViewOfFile m FILE_MAP_READ 0 0 0 if pfile NULL Step 4 Use the API to get the file name from the handle result GetMappedFileName GetCurrentProcess pfile buf buflen UnmapViewOfFile pfile CloseHandle m if result Step 5 Get the Translation for the device names char szTemp 1024 if GetLogicalDriveStrin
263. dinates to screen coordinates 342 Passing an argument to a dialog box procedure 342 Calling printf from a windows application 343 Enabling or disabling a button or control in a dialog box 343 Making a window class available for all applications in the system 343 Accessing the disk drive directly without using a file system 344 Retrieving the Last Write Time 344 Retrieving the file name from a FILE pointer 345 Setting the System Time 346 Getting the list of running processes 347 Changing a File Time to the Current Time 348 Converting from GMT UTC time to local time 348 Displaying the amount of disk space for each drive 349 Mounting and unmounting volumes in NTFS 5 0 350 FAQ 351 How do I create a progress report with a Cancel button 351 How do show in the screen a print preview 353 How do change the color of an edit field 354 How do I draw a transparent bitmap 354 How do I draw a gradient background 357 How do calculate print margins 358 How do calculate the bounding rectangle of a string of text 358 How do close an open menu 359 How do center a dialog box in the screen 359 How do create non rectangular windows 360 How do implement a non blinking caret 360 How do create a title window splash screen 360 How do append text to an edit control 364 How do I determine the color settings 365 How do spawn a process with redirected stdin and stdout 365 How to modify the width of the list of a combo box 366 How d
264. dog break case MOUSE printf This is a mouse break default printf Unknown animal break We define an enumeration of symbols and call another function that asks for an animal type to the user and returns its code We dispatch then upon the value of the In this case the integer expression that controls the switch is just an integer but it could be any expression Note that the parentheses around the switch expression are mandatory The compiler generates code that evaluates the expression and a series of jumps gotos to go to the corresponding portions of the switch Each of those portions is introduced with a case keyword that is followed by an integer constant Note that no expressions are allowed in cases only constants that can be evaluated by the compiler during compilation Cases end normally with the keyword break that indicates that this portion of the switch is finished Execution continues after the switch A very important point here is that if you do not explicitly write the break keyword execution will continue into the next case Sometimes this is what you want but most often it is not Beware An example for this is the following switch ch case a case e case vowelCount t a i case o case u A closer view 65 break Here we have the same action for 5 cases and we use to our advantage this feature There is a reserved word default that
265. dows sockets interface 3 1 1 What is a network Let s start with a short review of the basic network terminology The figure below demon strates a simple network that you might find in a small business or in the home Each machine has a network adapter that connects it to the network as well as a name that uniquely identifies it The network adapter determines the type of network generally either Ethernet WI FI or older types of networks like Token Ring The adapter also controls the media used for the net work coax twisted pair radio waves etc The important thing to recognize is that all of the machines in a simple network like this can communicate with all of the others equally A simple network 388 C Tutorial The machines send electrical signals through the medium used by the network be it coax twisted pair or radio waves This signals are encoded in precise bit patterns called protocols that give meaning to the bit stream To comunicate with one another machines follow specific rules for speech unlike people The slightest interference the slightest error in the sequence and the machines lose completely the conversation and get stuck Protocols are the base of all the network Many protocols have been used in the PC from the early LANMAN days to now where TCP IP has displaced all others With the rise of the internet the internet protocol has been accepted as a quasi universal stan dard This protocol runs
266. dvice but other compilers will ignore it and use their own schema In general you can t rely that the register keyword means that the variable is not stored in memory 1 13 15 Sizeof The result of sizeof is an unsigned constant integer calculated at compile time For instance sizeof int will yield under Icc win the constant 4 In the case of a variable length array however the compiler can t know its size on advance and it will be forced to generate code that will evaluate the size of the array when the program is running For example int fn int size int tab size Here the compiler can t know the size of tab in advance The maximum size of an object for an implementation is given by the macro SIZE_MAX defined in limits h Lcc win defines this as 4GB but in 32 bit systems the actual maximum will be much lower than that In 64 bit operating systems a 32 bit program running an emula tion layer can have all the addressing space 4GB 1 13 16 Enum An enumeration is a sequence of symbols that are assigned integer values by the compiler The symbols so defined are equivalent to integers and can be used for instance in switch state ments The compiler starts assigning values at zero but you can change the values using the equals sign An enumeration like enum a b c will provoke that a will be zero b will be 1 and c will be 2 You can change this with enum a 10 b 25 c 76 1 13 17 Prototypes A prototype is a
267. e void result malloc size if result NULL fprintf sdterr No more memory left nProcessing stops n exit EXIT_FAILURE return result 130 C programming with Icc win32 Note that we keep the same signature i e the same type of result and the same type of argu ments as the original function we want to replace This is function sub classing Note too that we use fprintf instead of printf Fprintf takes an extra argument a file where the output should go We use the predefined file of standard error instead of the normal output file stdout that printf implicitly takes Why Because it is possible that the user redirects the output to a file instead of letting the output go directly to the screen In that case we would write our error messages to that file and the user would not see the error message 0 We change all occurrences of malloc by xmalloc and this error is gone We change too all other error reporting functions to take into account stderr But there are other issues Take for instance our finddata_t structure that we carry around in each STREAM structure What s its use We do not use it anywhere just copy it into our STREAM But why we introduced that in the first place Well we didn t really know much about findfirst etc and we thought it could be useful So we are stuck with it No not really Actually it is very easy to get rid of it We just change the structure STREA
268. e include lt stdio h gt unsigned char mybuf BUFSIZ BUFSIZ defined in stdio h int main void setbuf stdout mybuf 36 C programming with Icc win32 Note that the buffer is declared global Be careful about the scope of the buffer you pass to set buf You can use a buffer with local scope but you must be aware that before leaving the scope where the buffer is declared the file must be closed If not the program will crash when the fclose function tries to flush the contents of the buffer that is no longer available The fclose function will be called automatically at program exit if any open files exist at that time The setvbuf function allows you to change the mode of the buffering either line full or none and pass a buffer of a different size than BUFSIZ a constant defined in stdio h 1 9 5 1 Error conditions What is the proper way of finding an end of file condition while reading from a file Try to read the file and if it fails see if the reason it failed was end of file You find this using the feof function There are two reasons why a read from a file can fail The first one is that there is nothing more to read the end of the data set has been reached This means that the current position is at the end of the file The second reason is that there is a hardware error that makes any read ing impossible the disk drive has a bad spot and refuses to give any data back or the device underlying this file
269. e p 0 fullname sizeof fullname 1 0 strncpy fullname stream gt Name sizeof fullname 1 strncat fullname sizeof fullname 1 p strncat fullname name sizeof fullname 1 result fopen fullname mode if result NULL fprintf stderr Impossible to open s n fullname exit EXIT_FAILURE return result If pis NULL we will initialize the first char of fullname to zero Then execution continues at the strncat call after the else statement and we will copy at most sizeof fullname 1 chars into it overwriting the zero and maybe leaving the fullname character array without the termi nating zero if the length of the passed buffer is bigger than the size of fullname That could lead to a crash in fopen that surely expects a well formed string The solution is to finish the fullname buffer in ALL cases FILE Fopen STREAM stream char name char mode FILE result char fullname 1024 p p strrchr stream gt Name fullname sizeof fullname 1 0 if p NULL fullname 0 0 else p 0 strncpy fullname stream gt Name sizeof fullname 1 strncat fullname sizeof fullname 1 p strncat fullname name sizeof fullname 1 result fopen fullname mode if result NULL fprintf stderr Impossible to open s n fullname exit EXIT_FAILURE return result Never forget to
270. e amp Joe pJoe gt weight means 1 Fetch the contents of the pJoe pointer 2 Using that address add to it sizeof Name MAXNAME sizeof int sizeof bool 3 Retrieve from the updated memory location a double value Pointers 83 The operation 2 is equivalent to finding the offset of the desired field within a given structure This is often required and the language has defined the macro offsetof in the stddef h header file for using it within user s programs Pointers can be used to retrieve not only a portion of the object operation gt but to retrieve the whole object using the notation In the example above the operation pJoe would yield as its result the whole structure This operation dereferences the pointer and retrieves the entire object it is pointing to making it the exact opposite of the amp address of operator Only two kinds of arithmetic operations are possible with machine addresses Addition or sub traction of a displacement or subtraction of two machine addresses No other arithmetic oper ators can be applied to pointers 1 15 1 1 Addition or subtraction of a displacement pointer arithmetic Adding a displacement an integer to a pointer means Using the address stored in that pointer find the lt nth gt object after it If we have a pointer to int and we add to it 5 we find the 5th integer after the integer whose address was stored in the poin
271. e x is not required and will be ignored by the compiler Functions can have a variable number of arguments The function printf is an example of a function that takes several arguments We declare those functions like this int printf char The ellipsis means some more arguments 30 Why are function declarations important When I started programming in C prototypes for functions didn t exist So you could define a function like this int fn int a return a 8 and in another module write fn 7 9 without any problems Well without any problems at compile time of course The program crashed or returned non sense results When you had a big system of many modules written by several people the probability that an error like this existed in the program was almost 100 It is impossible to avoid mistakes like this You can avoid them most of the time but it is impossible to avoid them always 30 The interface for using functions with a variable number of arguments is described in the standard header file stdarg h See Functions with variable number of arguments on page 54 24 C programming with Icc win32 Function prototypes introduced compile time checking of all function calls There wasn t any more this dreaded problem that took us so many debugging hours with the primitive debugger of that time In the C language the compiler will abort compilation if a function is u
272. e BuildTree procedure as follows int BuildTree HWND parent HWND Start GetDesktopWindow HWND hTree GetDlgItem parent IDTREEWINDOW TV_INSERTSTRUCT TreeCtrlitem HTREEITEM hNewNode SendMessage hTree WM_SETREDRAW 0 0 A more complex example a clone of spy exe 277 TreeView_DeleteAllItems hTree memset amp TreeCtrliItem 0 sizeof TreeCtrlItem TreeCtrlitem hParent TVI_ROOT TreeCtrlitem hinsertAfter TVI_LAST TreeCtrliItem item mask TVIF_TEXT TVIF_PARAM TreeCtrlItem item pszText Desktop hNewNode TreeView_InsertItem hTree amp TreeCtrliItem Start GetWindow Start GW_CHILD Scan hTree hNewNode Start TreeView_Expand hTree hNewNode TVE_EXPAND SendMessage hTree WM_SETREDRAW 1 0 return 1 We enclose all our drawing to the control within two calls to the SendMessage function that tell essentially the tree control not to redraw anything The third parameter i e the wParam of the message is a Boolean flag that indicates whether redrawing should be on or off This solves the second problem After setting the redraw flag to off we send a command to the control to erase all items it may have This solves our first problem Here is the output of the program after we press the Scan menu item E windowtree OE x File Help Desktop BaseBar tool
273. e It names either an action a piece of data an enumeration of several possible states etc The C language uses the following rules concerning names bd 1 The letters allowed are A Z a z and the underscore character _ 2 Digits are allowed but no identifier starts with a digit 3 Lower case and upper case letters are considered different 4 Icc win has 255 characters for the maximum length of a name The standard guarantees 31 significant characters for an external identifier 63 for an internal one If you use overly long names your code may not work in other environments Identifiers are the vocabulary of your software When you create them give a mnemonic that speaks about the data stored at that location Here are some rules that you may want to follow eMost of the time construct identifiers from full words joined either by underscore or implicitly separated by capitalization For example 1ist_element or ListElement A variant of this rule is camel casing the first word is in lower case the second starts with upper case In this example we would have listElement Use abbreviations sparingly for words you use frequently within a package As always be consistent if you do so eIdentifier names should grow longer as their scope grows longer Identifiers local to a function can have much shorter names than those used throughout a package eIdentifiers containing a double underscore __ or beginning with
274. e lt qfloat h gt include lt stdio h gt int main void qfloat f 34 fctf fctf factq f f fctft 1 if fctf f printf OK n else printf Not ok n return 0 This prints OK at the first try Using the extremely precise qfloat representation we obtain gaps smaller than 1 even when the magnitude of the numbers is 10 i This extension of lcc win allows you to use extremely precise representation only in the places where it is needed and revert to other formats when that precision is no longer needed 1 37 2 3 Going deeper Let s take a concrete example 178 125 Suppose this program include lt stdio h gt No compiler alignment pragma pack 1 In this structure we describe a simple precision floating point number typedef union float f1 struct unsigned 23 fraction part unsigned e 8 exponent part unsigned sign 1 sign Ee number This function prints the parts of a floating point number in binary and decimal notation void pfloat number t xprintf Sign d exponent d 127 d fraction 023b n t sign t e t e 127 t f int main void 85 Note that there are as many IEEE754 numbers between 1 0 and 2 0 as there are between 2456 and 2457 in double format 2457 256 is quite a big number 72 057 594 037 927 936 86 This is an unnamed structure within another structure or union lcc win and other compilers like visual C allow to a
275. e pExm you can select the field debt_ratio using Exm debt_ratio If you have a pointer to a structure instead of the structure itself you use pExm gt debt_ratio This leads to an interesting question Why having two operators for selection It is obvious that the compiler can figure out that a pointer needs to be dereferenced and could generate the code as well if we would always write a point as in many other languages This 44 The general rule proposed by Chris Torek could be as follows If something is important give ita name If it is going to be used frequently give it a name If it is unimportant and will appear rarely especially just once try not to give it a name A closer view 71 distinction has historical reasons In a discussion about this in comp lang c Chris Torek one of the maintainers of the gcc C library wrote wow The true need for separate and gt operators went away sometime around 1978 or 1979 around the time the original K amp R white book came out Before then Dennis early compilers accepted things like this struct char a b int x 12345 yes no sign main printf d is made up of the bytes d and d n x x a amp 0377 x b amp 0377 in fact in an even earlier version of the compiler the syntax was struct rather than struct The syntax above is what appeared in V6 Unix I have read V6 code but never used the V6
276. e so that the usage of qsort is clear before we apply it to our frequencies problem include lt stdlib h gt 59 Finding out where is something defined can be quite a difficult task The easiest way is to use the IDE of Icc win right click in the identifier and choose goto definition If that doesn t work you can use grep to search in a set of files 102 C programming with Icc win32 include lt string h gt 1 include lt stdio h gt int compare const void argl const void arg2 2 Compare all of both strings 3 return stricmp char argl char arg2 int main int argc char argv Eliminate argv 0 from sort 4 argvtt argc Sort remaining args using qsort 5 qsort void argv size_t argc sizeof char compare Output sorted list for int i 0 i lt argc i 6 printf s argv i printf n 7 return 0 The structure of this example is as follows We build a program that will sort its arguments and output the sorted result To use qsort we define a comparison function that returns an integer which encodes the rela tive lexical ordering of the two arguments passed to it We use a library function for doing that the stricemp function that compares two character strings without caring about case differ ences But there is quite a lot of new material in this example and it is worth going through i
277. e 57 otherwise expr exprl Multiply expr by expr and store the result in expr a 7 expr exprl Divide expr by expr1 and store the result in expr a 78 Calculate the remainder of expr expr and store o expr exprl a 6 the result in expr expr exprl Add expr with expr and store the result in expr a 6 expr exprl Subtract exprl from expr and store the result in expr a 76 Shift left expr by expr bits and store the result in expr lt lt expri a lt lt 6 expr Spr roS dees Shift right expr by expr1 bits and store the result in fg Sa expr Bitwise and expr with expr and store the result in expr amp exprl a amp 32 expr Bitwise xor expr with expr and store the result in expr ss exprl P P a 64 expr ae ee Bitwise or expr with expr and store the result in a 128 expr Evaluate expr then expr and return the result of a 7 b 8 expr exprl evaluating the last expression in this case exprl The result of See page 68 this is 8 Null statement 7 1 Variable can be any value that can be assigned to an array element or other constructs like ptr 5 In technical language this is called an lvalue An overview of the whole language 43 1 11 2 Declarations Declarations Meaning Example Identifier will have the specified type within this neid scope In a local scope its value is Sipe ees ype g undetermined In a global scope its initial value i ae is zero at pr
278. e any need to encode its contents unlike MIME or UUENCODE The problem with ftp is that it is very slow to start high latency and needs when using manually a lengthy login procedure The current standard for FTP is RFC 959 which obsoleted the previous specification RFC 765 The first FTP specification was RFC 114 written by A Bhushan in the MIT project MAC the 16 April 1971 Yes It is a really old protocol 3 4 1 Implementing the ftp GET We use a simple interface again ignoring all complexities GetFtpUrl needs 3 arguments 1 The name of the host 2 The name of the file to get 3 The name of the local file where the remote file will be written int GetFtpUrl char host char infile char outfile HINTERNET hOpen hConnect int fret 1 The first thing to do is to check that there is an internet connection If the local machine is not connected to the internet a call to this function will bring up a dialog box and a series of wizards to set up the connection fret InternetAttemptConnect 0 if fret return fret We can assume now that an internet connection exists We initialize the inet library specifying the default proxy settings and using some character string as the name of the user agent hOpen InternetOpen FTP lec INTERNET_OPEN_TYPE_PRECONFIG NULL 0 0 if hOpen return 1 We establish now the connection using the default FTP
279. e assembler code generated by our floating point program we notice while fctf f fctf flds 16 ebp loads fctf in the floating point unit fadds 4 Sebp adds f to the number stored in the FPU fcomps 16 ebp compares the sum with fctf Looking at the manuals for the pentium processor we see that the addition is done using the full FPU precision 80 bits and not in floating point precision Each number is loaded into the FPU and automatically converted to a 80 bits precision number We modify our program to avoid this int main void float f fctf sum fctf factf 34 0f f 1 0 sum f fctf while fctf sum f 2 0 sum fctf f printf Needs e n return 0 Note that this modified program is mathematically equivalent to the previous one When we run it we obtain Needs 1 014120e 031 OK now we see that the gap between numbers using the float format is much bigger than the one with double precision Note that both versions of the program are mathematically equivalent but numerically completely different Note too that the results differ by 12 orders of magnitude just by modifying slightly the calcu lations We modify our program for double precision and now we obtain Needs 3 777893e 022 Numerical programming 199 The gap using double precision is much smaller 9 orders of magnitude than with single pre cision gt Using qfloats now we write includ
280. e back to the IDE and we start reading the generated program in more detail It has three functions e WinMain e InitializeApp e DialogFunc If we ignore the empty function InitializeApp that is just a hook to allow you to setup things before the dialog box is shown only two functions need to be understood Not a very difficult undertaking I hope 2 1 1 WinMain Command line programs those that run in the ill named msdos window use the main function as the entry point Windows programs use the WinMain entry point 100 The arguments WinMain receives are a sample of what is waiting for you They are a mess of historical accidents that make little sense now Let s look at the gory details int APIENTRY WinMain HINSTANCE hinst HINSTANCE hinstPrev LPSTR lpCmdLine int nCmdShow This is a function that returns an int uses the stdcall calling convention denoted by APIEN TRY and that receives from the system 4 parameters hinst a HANDLE to an instance of the program This will always be 0x400000 in hexadec imal and is never used But many window functions need it so better store it away 99 This has only historical reasons from the good old days of windows 2 0 or even earlier You can use main as the entry point and your program will run as you expect but traditionally the entry point is called WinMain and we will stick to that for now 100 A calling convention
281. e following expression should be executed EXCEPTION_CONTINUE_SEARCH 0 means that the system should go on looking for another handler EXCEPTION_CONTINUE_EXECUTION 1 means that the system should attempt to go on at the same point in the program where the exception happened In this case we decided that any exception would provoke the execution of the block following the __ except 1 36 5 3 Auxiliary functions Of course you are surely keenly interested in the actual exception code The pseudo function GetExceptionCode will return the current exception code If we change our program to include lt stdio h gt include lt seh h gt int main void char p NULL unsigned code __try p 0 printf No exceptions n _ except code GetExceptionCode EXCEPTION_EXECUTE_HANDLER printf Ooops there was a problem with this program printf Error code x n code return 0 This will print Ooops there was a problem with this program Error code 0xc0000005 We use a comma expression within the except to catch the value of the exception code into a local variable The comma expression returns EXCEPTION_EXECUTE_HANDLER as its result with the side effect of storing the exception code in a local variable In other compilers the GetExceptionCode function can be called only within an except expression Lcc win let s you c
282. e have a stack layout like this 71 Some people would say that this is not Standard C since the standard doesn t explicitly allow for this But I would like to point out that the standard explicitly states page 96 of my edition that An implementation may accept other forms of constant expressions The implementation Icc win then is free to accept the above declaration as a constant expression 136 C programming with Icc win32 local variables of the calling function arguments to the current function return address saved frame pointer local variables p is at the lowest address then fullname then result saved registers stack pointer is here An overflow when copying the Name field would destroy the saved frame pointer and maybe destroy the return address The copy starts at the lowest address the start of the fullname buf fer then goes on to higher addresses After the overflow occurs the function would continue normally until it executes the return statement Depending on the type of overflow the return address would contain characters from the Name field that in most cases would lead to a wrong return address and a program crash But that is not always the case It could be that a user of our program would notice this style of programming and give us a file name that when overflowing in the copy to the temporary buffer would form a correct return address that would pass then control to some other routi
283. e just pass BF ID_USENEWUL meaning that we want the shell to use the improved user interface with drag and drop new folder the possibility of deleting folders whatever And we are done with the filling of the structure We just have to call our famous SHBrowseForFolder and assign the result to ItemIdList Here is an image of the user interface display that appears in a windows 2000 machine in other versions of windows it will look different The user interface is quite sophisticated and it is all at our disposal without writing any code well almost What is better even if we had spent some months developing a similar thing we would have to maintain it test it etc Note that you can transparently browse the network give a symbolic path like My computer or other goodies Desktop He My Computer Ball 3 Floppy A nS Local Disk C ce Local Disk D If the call worked i e if the user interface returns a valid pointer and not NULL we should translate the meaningless stuff we receive into a real path so we call SHGetPathFro mIDList to do exactly that We pass it a pointer to the result character string that we receive as second argument If that function returns OK we verify that the returned path is not empty and if it is we set the result of this function to TRUE Now we have to clean up We use the COM interface pointer we received from SHGetMal loc and use its only member IpVtbl to get into the Free f
284. e like a path to some location 82 C programming with Icc win32 Pointers must be initialized before use by making them point to an object Before initialization they contain a NULL value if they are defined at global scope or an undefined value if they are local variables It is always a very bad idea to use an uninitialized pointer Memory locations are dependent on the operating system the amount of memory installed and how the operating system presents memory to the programmer Never make many assumptions about memory locations For instance the addresses we see now under windows 32 bit could radically change in other context where they become 64 bit addresses Anyway under Win32 we use virtual memory so those numbers are virtual addresses and not really memory locations inside the circuit board See the description of virtual memory under win dows page 143 A pointer can store the start address of an object but nothing says that this object continues to exist If the object disappears the pointers to it contain now invalid addresses but it is up to the programmer to take care of this An object can disappear if for instance its address is passed to the free function to release the memory An object can disappear if its scope i e the function where it was defined ends It is a beginner s mistake to write int fn int a int a return amp a The a variable has a duration defined until the function f
285. e name gt This is MUCH clearer than the incomprehensible message box from the system isn t it Now let s try the following h lcc examples gt countchars zzzssqqqqq And we obtain the dreaded message box again Why Well it is very unlikely that a file called zzzssqqqqq exists in the current directory We have used the function fopen but we didn t bother to test if the result of fopen didn t tell us that the operation failed because for instance the file doesn t exist at all A quick look at the documentation of fopen that you can obtain by pressing F1 with the cur sor over the fopen word in Wedit will tell us that when fopen returns a NULL pointer a zero it means the open operation failed We modify again our program to take into account this possibility include lt stdio h gt include lt stdlib h gt int main int argc char argv int count 0 chars read FILE infile int c if arge lt 2 printf Usage countchars lt file name gt n exit EXIT_FAILURE infile fopen argv 1 r if infile NULL printf File s doesn t exist n argv 1 exit EXIT_FAILURE c fgetc infile while c EOF count c fgetc infile printf d n count return 0 We try again H lcc examples gt lcc countchars c H lcc examples gt lcclnk countchars obj H lcc examples gt countchars sfsfsfsfs File sfsfsfsfs doesn t exist H lcc exampl
286. e number of elements in any array is the size of that array divided by the size of each element Since all elements have the same size we can take any element to make the division Taking array 0 is the best one since that element is always present Now we can substitute the 256 by NELEMENTS Frequencies and even if we change our program to use Unicode with 65535 different characters and each character over two bytes our size will remain correct This construct like many others points to one direction making the program more flexible and more robust to change We still have our 256 in the definition of the array though We can define the size of the array using the preprocessor like this define FrequencyArraySize 256 This allows us later by changing this single line to modify all places where the size of the array is needed Lcc win allows you an alternative way of defining this static const int FrequencyArraySize 256 This will work just like the pre processor definition 1 28 Buffer overflows Let s come back to the code snippet above else p 0 strcpy fullname stream gt Name strcat fullname p strcat fullname name If the length of st ream gt Name is bigger than the size of the buffer a security hole appears the program will write over the local variables of the function and later over the return address stored in the stack when our function is active W
287. e number of rows but passing the number of columns like this int tab 6 This is the standard way of passing two dimensional arrays to a function For example include lt stdio h gt int tab 2 3 1 2 3 4 5 6 int fn int array 3 Note the declaration of the array parameter printf d n array 1 1 int main void fn tab Arrays can be fixed i e their dimensions are determined at compile time or they can be dynamic i e their dimensions are determined at run time For dynamic arrays we have to do a two stage process to allocate the storage that we need for them in contrast to one dimen sional arrays where we need just a single allocation For instance here is the code we would write to allocate dynamically an array of integers of 3 rows and 4 columns int result malloc 3 sizeof int for int i 0 i lt 3 i result i malloc 4 sizeof int Of course in a real program we would have always tested the result value of malloc for failure A closer view 53 We see that we allocate an array of pointers first that is equal to the number of rows we will need Then we fill each row with an allocation of space for the number of columns in the array times the size of the object we are storing in the array in this example an integer It is important to distinguish the difference between dynamically allocated and compile time fixed arrays The row major order formula does not work wit
288. e procedure for that class of objects to maintain a coherent view of the desktop and to avoid unnecessary code duplication at each window We are now ready to start our next project building a real window not just a simple dialog 2 7 Amore advanced window We will create the next example with the wizard too It is a handy way of avoiding writing a lot of boilerplate code But it is obvious that we will need to understand every bit of what the wizard generates We create a new project as usual with the project then Create menu option and we give it the name of winexample The wizard shows us a lot of dialogs with many options that will be explained later so just stick with the defaults Choose a single win dow application ype ot application E Single window gt Dialog based Console application wo After pressing the next button till the dialog boxes disappear we press F9 compile the whole and we run it We see a single white window with a status bar at the bottom a sum 118 In the data processing field we have been always recycling very old ideas as new just improved Object oriented programming was an idea that came from the old days of Simula in the beginning of the seventies but was rediscovered or rather reinvented in the late 80s Garbage collection was standard in lisp systems in the seventies and now has been discovered again by Mr Bill Gates in the next centur
289. e qsort call we call it and then we just print the results 77 Global variables like this should be used with care Overuse of global variables leads to problems when the application grows for instance in multi threaded applications When you got a lot of global variables accessed from many points of the program it becomes impossible to use threads because the danger that two threads access the same global variable at a time Another problem is that our global is not static but visible through the whole program If somewhere else somebody writes a function called words we are doomed In this case and for this example the global variable solution is easier but not as a general solution 158 C programming with Icc win32 1 31 4 Code review Now that we have a bare skeleton of our program up and running let s come back to it with a critical eye For instance look at our isWordStart function We have int isWordStart int c if c _ return 1 if c gt a amp amp c lt z return 1 if c gt A amp amp c lt Z return 1 return 0 A look in the ctype h system header file tells us that for classifying characters we have a lot of efficient functions We can reduce all this code to int isWordStart int c return c _ isalpha c The isalpha function will return 1 if the character is one of the uppercase or lowercase alphabetic characters Always use libra
290. e read this comment into the interface This features are just an aid to easy the writing of comments and making them uniform and structured As any other feature you could use another format in another environment You could make a simple text file that would be inserted where necessary and the fields would be tailored to the application you are developing Such a solution would work in most systems too since most editors allow you to insert a file at the insertion point 1 11 An overview of the whole language Let s formalize a bit what we are discussing Here are some tables that you can use as refer ence tables We have first the words of the language the statements Then we have a diction ary of some sentences you can write with those statements the different declarations and control flow constructs And in the end is the summary of the pre processor instructions I have tried to put everything hoping that I didn t forget something You will find in the left column a more or less formal description of the construct a short explanation in the second column and an example in the third In the first column this words have a special meaning id meaning an identifier type meaning some arbitrary type and expr meaning some arbitrary C expression I have forced a page break here so that you can print these pages separately when you are using the system 1 11 1 40 C programming with Icc win32 Statements E
291. e server and other system information Note that you must be the administrator user to be able to modify this tree 4 HKEY_USERS Registry entries subordinate to this key define the default user configuration for new users on the local computer and the user configuration for the current user 5 HKEY_CURRENT_CONFIG Contains information about the current hardware profile of the local computer system The information under HKEY_CURRENT_CONFIG describes only the differences between the current hardware configuration and the standard configuration Information about the standard hardware configuration is stored under the Software and System keys of HKEY_LOCAL MACHINE Actually this key is an alias for HKEY_LOCAL_MACHINE System CurrentControlSet Hardware Profiles Current This keys provide you with an entry point into the registry To open a key you must supply a handle to another key in the registry that is already open The system defines predefined keys that are always open Those keys help you navigate in the registry and make it possible to develop tools that allow a system administrator to manipulate categories of data Applications that add data to the registry should always work within the framework of predefined keys so administrative tools can find and use the new data 2 16 2 Enumerating registry subkeys The following example demonstrates the use of the RegQueryInfoKey RegEnumKeyEx and RegEnum Value functions The hKey
292. e systems not Modern windows file systems allow you to track file operations and access their journal data You can encrypt data and at last under windows 2000 Unix s mount operation is recognized You can establish symbolic links for files i e consider a file as a pointer to another one This pointer is dereferenced by the file system when accessing the link File systems Windows supports several file systems 1 NTFS NTES is the preferred file system on Windows It was designed to address the requirements of high performance file servers and server networks as well as desktop computers and in doing so address many of the limitations of the earlier FAT16 and FAT32 file systems 318 C Tutorial 2 FAT32 The File Allocation Table FAT file system organizes data on fixed disks and floppy disks The main advantage of FAT volumes is that they are accessible by MS DOS Windows and OS 2 systems FAT is the only file system currently supported for floppy disks and other removable media FAT32 is the most recently defined FAT based file system format and it s included with Windows 95 OSR2 Windows 98 and Windows Millennium Edition FAT32 uses 32 bit cluster identifiers but reserves the high 4 bits so in effect it has 28 bit cluster identifiers 3 UDF file system The implementation is compliant with ISO 13346 and supports UDF versions 1 02 and 1 5 OSTA Optical Storage Technology Association defined UDF in 1995 as a format to replace CD
293. e technique as above We pass to the API a buffer of a given length and if it doesn t suffice we allocate the buffer in the returned length 3 pAdapterInfo malloc sizeof IP_ADAPTER_INFO ulOutBufLen sizeof IP_ADAPTER_INFO rc GetAdaptersInfo pAdapteriInfo amp ulOutBufLen if rc ERROR_SUCCESS free pAdapterInfo 396 C Tutorial pAdapteriInfo malloc dwRetVal GetAdaptersInfo pAdapterInfo if dwRetVal NO_ERROR printf Call GetLastError return 1 pAdapter pAdaptertInfo ulOutBufLen i amp ulOutBufLen to GetAdaptersInfo failed nError d n We have now a linked list of adapters Go through that list printing the information while pAdapter printf tAdapter Name t s n pAdapter gt AdapterName printf tAdapter Desc t s n pAdapter gt Description printf tAdapter Addr t x n pAdapter gt Address printf tIP Address t s n pAdapter gt IpAddressList IpAddress String printf tIP Mask t s n pAdapter gt IpAddressList IpMask String printf tGateway t s n pAdapter gt GatewayList IpAddress String if pAdapter gt DhcpEnabled printf tDHCP Enabled Yes n printf t tDHCP Server t s n pAdapter gt DhcpServer IpAddress String printf tLease Obtained ld n pAdapter gt LeaseObtained else printf tDHCP Enabled No n if pAdapter gt Have
294. e that do not like to click around a lot The printf function deposits characters in the input buffer of the terminal emulation program that makes the necessary bits change color using the current font and at the exact position needed to display each glyph Windows calls the graphic drivers in your graphic card that control the video output of the machine with those bits to change The bits change before your hand has had the time to move a millimeter Graphic drivers are fast today and in no time they return to windows that returns control to the printf function The printf function exits then control returns to main that exits to the startup that calls Exit Process and the program is finished by the operating system Your hand is still near the return key We have the following phases in this process 1 Design time We wrote the program first 2 Compile time We compiled our design 3 Run time The compiled instructions are started and the machine executes what we told it to do 1 3 5 1 We wrote the program first The central point in communicating with a printed circuit is the programming language you use to define the sequence of operations to be performed The sequence is prepared using that language first in your own circuit your brain then written down with another the keyboard controller then stored and processed by yet another a personal computer PC 1 3 5 2 We compiled our design Compiled languages rely on
295. e whole expression is the value of the second or third operand whichever is evaluated converted to the type described below If both the second and the third operand have an arithmetic type the result of the expression has that type If both are structures the result is a structure If both are void the result is void These expressions can be nested int a c 66 534 698 the integer a will be assigned 534 if c is equal to 66 otherwise it will be assigned 698 struct b bb bstruct NULL NULL b gt next If bstruct is different than NULL the pointer bb will receive the next field of the structure otherwise bb will be set to NULL 1 13 11 Struct A structure or a union can t contain another structure that hasn t been fully specified but they can contain a pointer to such a structure since the size of any pointer is always fixed To build recursive structures like list you should specify a pointer to the structure see Lists on page 163 For a detailed description of this keyword see Structures on page 110 1 13 12 Union You can store several values in a single memory location or a group of memory locations with the proviso that they can t be accessed at the same time of course This allows you to reduce the memory requirements of a structure or to interpret a sequence of bits in a different fash ion For a detailed discussion see Unions on page 115 1 13 13 Typedef The typed
296. e windows system for windows 95 98 for instance 1 30 5 The malloc with no free strategy This strategy uses only malloc never freeing any memory It is adapted to transient programs i e programs that do a well defined task and then exit It relies on the operating system to reclaim the memory used by the program Advantages 1 Simplified programming since all the code needed to keep track of memory blocks disappears 2 Itis fast since expensive calls to free are avoided Drawbacks 1 The program could use more memory than strictly needed 2 Itis very difficult to incorporate software using this strategy into another program i e to reuse it This strategy can be easily converted into an arena based strategy though since only a call to free the arena used by the program would be needed It is even easier to convert it to a garbage collector based memory management Just replace malloc by GC_malloc and you are done 1 30 6 Automatic freeing garbage collection This strategy relies upon a collector i e a program that scans the stack and the global area of the application looking for pointers to its buffers All the memory blocks that have a pointer to them or to an inner portion of them are marked as used the others are considered free This strategy combines easy of use and reclaiming of memory in a winning combination for most applications and it is the recommended strategy for people that do not feel like messing around i
297. ears ago when saving every cycle of machine time was of utmost importance Pushing an extra argument in this case the address of the Frequencies array takes 1 cycle At a speed of 1400 2500 MHz this cycle isn t a high price to pay Continuing our analysis of our main function we notice that the next task is displaying the output of the frequencies array This is quite a well defined task since it takes the array as input and should produce the desired display We define then a new function DisplayOut put that will do that Its single parameter is the same Frequencies array void DisplayOutput CHARS Frequencies for int count 0 count lt 256 count if Frequencies count Frequency 0 printf 3c 4d d n Frequencies count CharacterValue Frequencies count CharacterValue Frequencies count Frequency Let s look at our main function again int main int argc char argv int count FILE infile checkargs argc argv if infile NULL return 1 Initialize count ProcessFile infile Frequencies fclose infile printf d chars in file n count qsort Frequencies 256 sizeof CHARS compare DisplayOutput Frequencies 124 C programming with Icc win32 Note how much clearer our main function is now Instead of a lot of code without any struc ture we find a much smaller procedure that is constructed from smaller and easily understand able
298. ed the loader calls a function of the library to allow load time initializations This allows us to register our class for instance or do other things e When the program that loads them starts or ends a new thread the system arranges for calling the same function This allows us to take special actions when this event occurs We do not need this feature for our application here but other software do e When the library is unloaded either because the program explicitly does it or because simply the program is finished we get notified Here we can reverse the actions we performed when the library was loaded we can for instance unregister our window class e DLLs can contain resources This solves the problem of forcing the user of the library to link a bunch of resources to his her program DLLs need to specify which functions are going to be exported i e made visible to the outside world With static libraries this is not really necessary since the librarian will write all the sym bols with the external type to the library symbol table automatically 4 We can declare that a symbol will be exported using two methods 1 We can put in the declaration of the symbol the __declspec dllexport mark 2 We can write the name of the symbol in a special file called definitions file with the def extension and pass this file to the linker Which method you use is a matter of taste Writing __declspec dllexport in the source code is
299. ed a drive we can unmount it with the following utility include lt windows h gt include lt stdio h gt int main int argc char argv BOOL bFlag char mpath 512 if argc 2 printf s unmounts a volume from the volume mount point n argv 0 printf For example numount c mnt cdrom n return 1 strncpy mpath argv 1 sizeof mpath 3 mpath sizeof mpath 2 0 if mpath strlen mpath 1 strcat mpath bFlag DeleteVolumeMountPoint mpath printf Ss s in unmounting the volume at s n argv 0 bFlag Succeeded failed mpath return bFlag 2 22 FAQ Here are some answer to questions users of Icc win have asked or questions that I imagine you will find useful 2 22 1 How do l create a progress report with a Cancel button Here is the answer from the MSDN Knowledge base article Q76415 352 C Tutorial The following article describes the mechanisms necessary to implement a progress or activity indicator with a Cancel Operation option to be used for lengthy and CPU intensive subtasks of an application Examples of operations using this include copying multiple files directory searches or printing large files The progress dialog box is implemented in two steps e Initialize the dialog box before starting lengthy or CPU intensive subtask e After each unit of the subtask is complete call Progress Yield to determine if the user has
300. ee page 170 b a else the else branch of an if or ifdef else elif Abbreviation of else if elif endif End an if or ifdef preprocessor anaes directive statement error text Writes an error message See pe ae undefined file foo c Set the file name file ff c include lt header h gt Insert the contents of the given file from the standard include directory into the program text at this position include lt stdio h gt Insert the contents of the given file from include header h include foo h the current directory If the given identifier is defined using ifdef id define include the following lines ifdef TAX Else skip them See page 171 ifndef id The contrary of the above ifnef TAX Evaluate expression and if the result is if expr TRUE include the following lines Else if TAX 6 p skip all lines until finding an else or endif line nn Set the line number to nn line 56 Token concatenation a b ab token Make a string with a token Only valid foo gt foo within macro declarations pragma instructions Special compiler directives pragma optimize on _Pragma string Special compiler directives This is a C99 feature _Pragma optimize on undef id Erase from the pre processor tables the given identifier undef TAX 46 C programming with Icc wi
301. eele Jr If you are a professional that wants to get all the C language described in great detail this book is for you It covers the whole grammar and the standard library with each part of it described in detail The C programming language Brian W Kernighan Dennis Ritchie second edition This was the first book about C that I got and it is still a good read With many exercises it is this tutorial in a better rendering A retargetable C compiler design and implementation Chris Fraser and Dave Hanson This book got me started in this adventure It is a book about compiler construction and not really about the C language but if you are interested in knowing how Icc win works this is surely the place to start C interfaces and implementations David R Hanson 226 C programming with Icc win32 This is an excellent book about many subjects like multiple precision arithmetic lists sets exception handling and many others The implementation is in straight C and will compile without any problems in Icc win Safer C Les Hatton As we have seen in the section Pitfalls of the C language C is quite ridden with problems This book address how to avoid this problems and design and develop you work to avoid get ting bitten by them C Programming FAQs Steve Summit C Programming FAQs contains more than 400 frequently asked questions about C accompa nied by definitive answers Some of them are distributed
302. ef keyword defines a name that can be used as a synonym for a type or derived type In contrast to the struct union and enum declarations typedef declarations doesn t introduce new types it introduces new names for existing types 1 13 14 Register This keyword is a recommendation to the compiler to use a machine register for storing the values of this type The compiler is free to follow or not this directive The type must be either an integer type or a pointer If you use this declaration note that you aren t allowed to use the address of operator since registers do not have addresses Lcc win tries to honor your recom mendations but it is better not to use this declaration and leave the register usage to the com piler Registers are the highest part of your machine memory hierarchy They are the fastest storage available to the program by the circuit and in a PC x86 architecture there are just a few of them available at a time After registers there is the level 1 cache level 2 cache main memory then the disk in order of decreasing access speed A closer view 59 1 13 14 1 Implementation details The register keyword is no longer really necessary with the improvement of the compiler tech nology In most cases the compiler can figure out better than the user which variables should be stored in registers and which variables should be stored in memory Lcc win tries to honor the register keyword and it will follow your a
303. efined devices 28 The typical sequence of operations 29 Examples 29 Other input output functions 34 File buffering 35 Commenting the source code 36 Describing a function 37 Describing a file 38 An overview of the whole language 39 Statements 40 Declarations 43 Pre processor 45 Windows specific defined symbols 46 Structured exception handling 46 Control flow 47 Windows specific syntax 47 Extensions of Icc win 48 A closer view 49 Identifiers 49 Constants 49 Arrays 51 Compound literals 53 Function call syntax 54 Functions with variable number of arguments 54 Assignment 55 The four operations 56 Postfix 57 Conditional operator 57 Struct 58 Union 58 Typedef 58 Register 58 Sizeof 59 Enum 59 Prototypes 59 Const 60 Goto 60 Return 61 Unsigned 62 Bit fields 62 Stdcall 62 Break and continue statements 63 Null statements 63 Comments 64 Switch statement 64 Inline 65 Logical operators 65 Bitwise operators 66 Shift operators 67 Address of operator 67 Sequential expressions 68 Casts 68 Selection 70 Indirection 71 Predefined identifiers 73 Precedence of the different operators 73 The printf family 75 Conversions 75 The conversion flags 76 The size specification 77 The conversions 78 Scanning values 79 Pointers 81 Operations with pointers 82 Null pointers 84 Pointers and arrays 84 setjmp and longjmp 85 General usage 85 Register variables and longjmp 87 Simple programs
304. empty statement and we go out normally after the trap 84 The psignal function is not part of the standard but it exists in many implementation specially in UNIX systems Advanced C programming with Icc win 191 Note how this code starts to look very similar to the structured exception handling code The difference is that here we have to trap all possible signals then run our code then unset all the signals to their former values The only reason to prefer using signal to the structured exception handling is portability The signal mechanism will work in many other environments For instance the program above will run unmodified in a UNIX system producing the same output 192 C programming with Icc win32 1 37 Numerical programming Computers are done for making calculations well at least originally that was their objective Playing games internet browsing word processing etc came later The problem of storing numbers in a computer however is that the continuum of numbers is infinite and computers are limited Yes we have now many times the RAM amount that we had just a few years ago but that amount is finite and the numbers we can represent in it are just a finite approximation to the infinite mathematical continuum The moment we convert a problem from the domain of mathematical analysis to the range of numbers that can be handled in a machine even in a paper and pencil machine we are going to necessarily int
305. en src char pbEncodedBlob src content StringA result Open a message for decoding hMsg CryptMsgOpenToDecode MY_ENCODING_TYPE Encoding type 0 Flags CMSG_DATA Look for a data message NULL Cryptographic provider NULL Recipient information NULL if hMsg return 0 Update the message with an encoded BLOB Both pbEncodedBlob the encoded data FAQ 383 and cbEncodedBlob the length of the encoded data must be available if CryptMsgUpdate hMsg pbEncodedBlob cbEncodedBlob i TRUE return 0 Get the size of the content if CryptMsgGetParam hMsg CMSG_CONTENT_PARAM 0 NULL information amp cbDecoded return 0 Allocate memory pbDecoded malloc cbDecoded 1 Get a pointer to the content if CryptMsgGetParam hMsg CMSG_CONTENT_PARAM 0 pbDecoded information amp cbDecoded return 0 Clean up if hMsg CryptMsgClose hMsg src capacity cbDecoded 1 src count cbDecoded src content pbDecoded return 1 int Strencrypt String amp src PTMSG hMsg pbContent D cbContent The siz Handle to the message Pointer to the encoded BLOB Size of the encoded BLOB Last call Handle to the message Parameter type Index Address for returned Size of the returned Handle to the message Parameter type Index Address fo
306. ent band SetRect amp rectFill 0 Upper left X int iOnBand fStep Upper left Y rectClient right tl Lower right X int iOnBand 1 fStep Lower right Y Create a brush with the appropriate color for this band hBrush CreateSolidBrush RGB 0 0 255 iOnBand Fill the rectangle FillRect nDC amp rectFill hBrush Get rid of the brush you created DeleteObject hBrush Give back the DC ReleaseDC hWnd hDC 2 21 7 Capturing and printing the contents of an entire window iI Return a HDC for the default printer iI HDC GetPrinterDC void PRINTDLG pdlg 338 C Tutorial memset amp pdlg pdlg 1lStructSize sizeof PRINTDLG pdlg Flags PD_RETURNDEFAULT PD_RETURNDC PrintDlg amp pdlg return pdlg hDC 0 sizeof PRINTDLG Create a copy of the current system palette HPALETTE GetSystemPalette HDC hDC HPALETTE hPal HANDLE hLogPal PLOGPALETTE lpLogPal Get a DC for the desktop hDC GetDC NULL Check to see if you are a running in a palette based video mode if GetDeviceCaps hDC RASTERCAPS amp RC_PALETTE ReleaseDC NULL HDC return NULL Allocate memory for the palette lpLogPal GlobalAlloc GPTR sizeof LOGPALETTE 256 if hLogPal return NULL Initialize T sizeof PALETT ENTRY
307. er Size bytes Description qfloat qfloat h 56 352 bits floating point 23 In most compilers the char short int long types are present but their sizes can change from machine to machine Some embedded systems compilers do not support floating point Many compilers do not implement the recent types _Bool long long or long double Within the windows environment how ever the char short int long float double types are identical to this ones in all 32 bit windows compil ers I know of 24 Microsoft Visual C implements long double as double and calls the long long type __int64 To remain compatible with this compiler lcc win accepts __int64 as an equivalent of long long 20 C programming with Icc win32 bignum bignum h variable Extended precision number int128 int128 h 16 128 bit signed integer type numbers and their operations This is called operator overloading and will be explained further down Under lcc win 64 bits the sizes of the standard types change a bit We have Type sizes for lcc win 64 bits Type Size Comment bool char int long and long long Same as in the 32 bit version In the linux and AIX 64 bit versions of Icc win long is 64 bits pointer 8 64 bits All 64 bit versions have this type size long double 16 This type could not be maintained at 12 bytes since it would misalign the stack that must be alig
308. er loading of the brain memory cells lcc win proposes a stdheaders h file that consists of include lt assert h gt 17 In the user s manual there is an exhaustive list of the entire set of header files distributed with lcc win Please look there for an in depth view 7 10 C programming with Icc win32 include lt complex h gt etc Instead of including the standard headers in several include statements you just include the stdheaders h file and you are done with it True there is a very slight performance lost in compilation time but it is not really significant 1 4 2 Passing arguments to a program We can t modify the behavior of our hello program with arguments We have no way to pass it another character string for instance that it should use instead of the hard wired hello n We can t even tell it to stop putting a trailing new line character Programs normally receive arguments from their environment A very old but still quite effec tive method is to pass a command line to the program i e a series of character strings that the program can use to access its arguments Let s see how arguments are passed to a program 18 include lt stdio h gt 1 int main int argc char argv 2 int count 3 for count 0 count lt argc count 4 print 5 Argument d s n count argv count 6 return 0 1 We include again stdio h 2 We use a longer defin
309. er equal to zero hence an infinite loop 1 17 4 Write ispowerOfTwo without any loops After working hard to debug the above program it is disappointing to find out that it isn t the best way of doing the required calculation Here is an idea I got from reading the discussions in comp lang c isPow2 x amp amp x 1 amp x How does this work Algorithm If x is a power of two it doesn t have any bits in common with x 1 since it consists of a single bit on Any positive power of two is a single bit using binary integer representation For instance 32 is a power of two It is represented in binary as 100000 32 1 31 is represented as 011111 32 amp 31 is 100000 amp 011111 gt 0 52 Different than is written in C instead of The symbol wasn t included in the primitive typewriters in use when the C language was designed and we have kept that approximation It is consistent with the usage of as logical not i e would mean not equal 53 Fora more detailed discussion see the section News groups at the end of this tutorial 92 C programming with Icc win32 This means that we test if x 1 and x doesn t share bits with the and operator If they share some bits the AND of their bits will yield some non zero bits The only case where this will not happen is when x is a power of two Of course if x is zero not a power of two this doesn t hold so we add an explicit test for zero with the l
310. er of two this AND operation will return the value of that single bit Note too that 1 is a power of two since 2 to the power of zero is one We will return to this at the end of this section Coming back to our initialization procedure there are some new things besides this style set ting But this is just a matter of reading the windows documentation No big deal There are many introductory books that augment their volume just with the easy way of including a lot of windows documentation in their text Here we will make an exception But what is important however is that you know how to look in the documentation Suppose you want to know what the hell is that CS_DBLCLKS constant and what does it exactly mean You press F1 in that identifier and nothing It is not in the index Well this constant appears in the context of RegisterClass API When we look at the docu mentation of RegisterClass we find a pointer to the doc of the WNDCLASS structure Going there we find in the description of the style field all the CS_ constants neatly explained Note that not all is in the index You have to have a feeling of where to look Lcc win comes with a help file of reasonable size to be downloaded with a standard modem It is 13MB com pressed and it has the essentials A more detailed documentation complete with the latest stuff is in the Software Development Kit SDK furnished by Microsoft It is available at their Web site and it h
311. ere How we could do this If the argument contains backslashes it means there is a path component in it We could copy the string up to the last backslash and then change our current directory to that For instance if we find an argument like src77 c the path component would be src77 Here is an updated version of checkargs STREAM checkargs int argc char argv STREAM infile NULL long findfirstResult struct _finddata_t fd char p if arge lt 2 error handling elided else findfirstResult _findfirst argv 1 amp fd if findfirstResult lt 0 fprintf stderr File s doesn t exist n argv 1 j return NULL infile malloc sizeof STREAM infile gt Name argv 1 p strrchr argv 1 if p p 0 chdir argv 1 p 134 C programming with Icc win32 infile gt file fopen fd name rb infile gt handle findfirstResult return infile We use the library function strrchr That function will return a pointer to the last position where the given character appears in the input string or NULL if the given character doesn t appear at all Using that pointer we replace the backslash with a NULL character Since a zero terminates all strings in C this will effectively cut the string at that position Using that path we call another library function chdir that does what is name indicates changes the current direc
312. ers of 32 bits each called page description entry or PDE for short The PDE is used to get the address of another special page called page table The second group of bits 21 12 is used to get the offset in that page table Once the page frame found the remaining 12 bits are used to address an individual byte within the page frame Here is a figure that visualizes the structure Page Directory 4K a 1024 x 4096 4 MB 1024 x 1024 x 4096 4 G6 74 Note that this is a logical view of this address translation process The actual implementation is much more sophisticated since Windows uses the memory manager of the CPU to speed up things Please read the original article to get a more in depth view including the mechanism of page protection the working set and many other things 144 C programming with Icc win32 We see that a considerable amount of memory is used to manage memory To realize the whole 4GB address space we would use 4MB of RAM But this is not as bad as it looks like since Windows is smart enough to fill these pages as needed And anyway 4MB is not even 0 1 of the total 4GB address space offered by the system gt Each process has its own page directory This means that processes are protected from stray pointers in other programs A bad pointer can t address anything outside the process address space This is good news compared to the horrible situation under windows 3 1 or even MSDOS where a
313. es a b exprl gt expr2 1 if expr2 is greater than expr2 zero otherwise a gt b exprl expr2 1 if expr1 is equal to expr2 zero otherwise a exprl expr2 1 if expr1 is different from expr2 zero otherwise a b Bitwise AND expr1 with expr2 See Bitwise exprl amp expr2 5 a amp 8 operators on page 66 Bitwise XOR expr1 with expr2 See Bitwise 7 exprl expr2 3 a b operators on page 66 Bitwise OR expr1 with expr2 See Bitwise expri expr2 S a 16 operators on page 66 Evaluate expr1 If its result is zero stop evaluating a lt 5 amp amp a gt 0O the whole expression and set the result of the whole ooo betes This will be 1 if a is expe Se eos expression to zero If not continue evaluating expr2 between oA fast 4 The result of the expression is the logical AND of Ian 5 the second test is not the results of evaluating each expression See e performed Logical operators on page 65 Evaluate expr1 If the result is one stop evaluating the whole expression and set the result of the Seema pie expression to 1 If not continue evaluating expr2 ee Saas 1 2 ae Th ll be 1 if eith SRPEN N expr The result of the expression is the logical OR of the A aA 3 a eee results of each expression See Logical operators on page 65 If expr evaluates to non zero true return vall a b 2 3 expr vallival2_ otherwise return val2 a will be 2 if b is true 3 see Conditional operator on pag
314. es gt Well this error checking works But let s look again at the logic of this program Suppose we have an empty file Will our program work Input and output 33 If we have an empty file the first fgetc will return EOF This means the whole while loop will never be executed and control will pass to our printf statement Since we took care of initializ ing our counter to zero at the start of the program the program will report correctly the num ber of characters in an empty file zero Still it would be interesting to verify that we are getting the right count for a given file Well that s easy We count the characters with our program and then we use the DIR directive of windows to verify that we get the right count H lcc examples gt countchars countchars c 466 H lcc examples gt dir countchars c 07 01 00 11 31p 492 countchars c 1 File s 492 bytes Wow we are missing 492 466 26 chars Why We read again the specifications of the fopen function It says that we should use it in read mode with r or in binary mode with rb This means that when we open a file in read mode it will translate the sequences of characters r return and n new line into ONE character When we open a file to count all characters in it we should count the return characters too This has historical reasons The C language originated in a system called UNIX actually the whole language was developed to be able to write the UNIX
315. es with the increment part Remember that the continue statement within a switch statement doesn t mean that execution will continue the switch but continue the next enclosing for while or do statement 1 13 25 Null statements A null statement is just a semicolon This is used in two contexts 1 An empty body of an iterative statement while do or for For instance you can do while pt 64 C programming with Icc win32 search the end of the string 2 A label should appear just before a closing brace Since labels must be attached to a statement the empty statement does that just fine 1 13 26 Comments Multi line comments are introduced with the characters and and finished with the opposite sequence followed by This commentaries can t be nested Single line com ments are introduced by the sequence and go up to the end of the line Here are some examples a b Four character string literal Single line comment not syntax error f g h Equivalent to f g h fn Part of a comment since the last line ended with a 1 13 27 Switch statement The purpose of this statement is to dispatch to several code portions according to the value in an integer expression A simple example is enum animal CAT DOG MOUSE enum animal pet GetAnimalFromUser switch pet case CAT printf This is a cat break case DOG printf This is a
316. ething is lacking A nice way to use your keyboard After initializing the window class the WinMain function loads the accelerators for the appli cation This table is just a series of keyboard shortcuts that make easy to access the different menu items without using the mouse and leaving the keyboard In the resource editor you can edit them add delete change etc To do this you start the resource editor and you press the dir button in the upper right You will see the following display winexample rc ae Accelerator lt Here You click in the Accelerator tree tab and you will see the following Accelerator keys IDM_EXIT 7 p00 IDM_EXIT VIRTKEY CONTROL We have here the accelerator called IDM_EXIT that has the value of 300 This is just Ctrl Q for quit The key value is 81 the ASCII value of the letter q with a flag indicating that the control key must be pressed to avoid quitting just when the user happens to press the letter q in the keyboard A more advanced window 263 Double clicking in the selected line leads us to yet another dialog Changing an accelerator key Modifiers i Key fer gadoosgoos wt le Cancel Menu equivalent Type IDM_EXIT 7 C Ascii Virtual Key Change key Here you can change the accelerator as you want The flags are explained in the documenta tion for the resource editor But this was just another digression we were speaking a
317. evinstance void 0x1441e68 lpCmdLine O0xl43aa0 20 nCmdShow 4210720 hInst void 0x0 Now wait a minute our window procedure that receives the message from the system is called indirectly from Windows we can t just follow the program blindly If we did that we would end up in the main loop wasting our time 130 Why didn t we use the DLL to ask for the string to search Mostly because I wanted to give you an overview of the whole process A good exercise would be to change the program to use the DLL Which changes would be necessary How would you link Filling the blanks 293 No we have to set a breakpoint there We set a breakpoint when we call the dialog using the F2 accelerator key We see that Wedit sets a sign at the left to indicate us that there is a break point there Then we press F5 again to start running the program W wedit winexample winexample c File Edit Search Project Resources Debug Utils Modules Window Help 2 x return FALSE int DoSearchText char txt HessageBox NULL txt Text to search is MB_OK return 1 O 1 lt O The following code comes from hs Sloe 1ibywizend defor void MainWndProc_OnCommand HWND hwnd int id HWND hwndCtl switch id TODO Add new menu commands here case IDM _ SEARCH char text 1024 if CallDialog IDD_SEARCH SearchDlgProc LP DoSearchText text t break case IDM_EXIT PostMessage hwnd
318. expressed in terms of memory locations but in terms of the size of the objects For instance the distance between two consecutive objects is always one and not the number of memory locations that separates the start addresses of the two objects 84 C programming with Icc win32 The type of the result is an integer but it is implementation defined exactly which short int long etc To make things portable the standard has defined a special typedef pt rdiff_t that encapsulates this result type Under Icc win this is an int but under other versions of Icc win in 64 bit architectures for instance it could be something else 1 15 1 3 Relational operators Pointers can be compared for equality with the operator The meaning of this operation is to find out if the contents of two pointers are the same i e if they point to the same object The other relational operators are allowed too and the result allows to know which pointer appears before or later in the linear memory space Obviously this comparisons will fail if the memory space is not linear as is the case in segmented architectures where a pointer belongs to a memory region or segment and inter segment comparisons are not meaningful 1 15 2 Null pointers A pointer should either contain a valid address or be empty The empty value of a pointer is defined as the NULL pointer value and it is usually zero Using an empty pointer is usually a bad idea since it prov
319. f the file we wish to open and the mode that we want to open this file in our example in read mode Note that the mode is passed as a character string i e enclosed in double quotes 7 Once opened we can use the fgetc function to get a character from a file This function receives as argument the file we want to read from in this case the variable infile and returns an integer containing the character read 8 We use the while statement to loop reading characters from a file This statement has the general form while condition statements The loop body will be executed for so long as the condition holds We test at each iteration of the loop if our character is not the special constant EOF End Of File defined in stdio h 9 We increment the counter of the characters If we arrive here it means that the character wasn t the last one so we increase the counter 10 After counting the character we are done with it and we read into the same variable a new character again using the fgetc function 11 If we arrive here it means that we have hit EOF the end of the file We print our count in the screen and exit the program returning zero i e all is OK By convention a program returns zero when no errors happened and an error code when something happens that needs to be reported to the calling environment Now we are ready to start our program We compile it link it and we call it with h lcc examples gt
320. fer with a reasonable amount of storage Our function cleans the buffer before using it and then calls one of the workhorses of the dia log procedures the API GetDlgItemText This versatile procedure will put in the designated buffer the text in a control window in this case the text in the entry field We again indicate to the API which control we are interested in by using its numerical ID Note that GetDlgItem Text returns the number of characters read from the control If there isn t anything the user pressed OK without entering any text GetDlgItemText returns zero The first time that we do that we will surely will want to verify that the text we are getting is the one we entered To do this we use the API MessageBox that puts up a message in the screen without forcing us to register a window class define yet another window procedure etc We add then to our window procedure the following lines case IDOK if ReadText hwndDlg MessageBox hwndDlg buffer text entered MB OK 240 C Tutorial EndDialog hwndDlg 1 return 1 MessageBox takes a parent window handle in this case the handle of the dialog box proce dure a buffer of text a title of the message box window and several predefined integer con stants that indicate which buttons it should show We want just one button called OK so we pass that constant Note too that if the user entered no text we do NOT call the EndDialog API so the dialog
321. first solution To be really clear the OK button should start disabled but become active immediately after the user has typed some text If during editing the user erases all text that has been entered the OK button should revert to its inactive state We can do this by processing the messages that our edit field sends to us Edit fields are very sophisticated controls actually a full blown mini editor in a small window Each time the user types anything in it the edit field procedure sends usa WM_COMMAND message informing us of each event We change our dialog procedure as follows case WM_COMMAND switch LOWORD wParam case IDOK suppressed stays the same case IDCANCEL EndDialog hwndDlg 0 return 1 case IDENTRYFIELD switch HIWORD wParam case EN_CHANGE if GetDlgItemText hwndDlg IDENTRYFIELD buffer sizeof buffer Introduction to windows programming 241 inableWindow GetDlgItem hwndDlg IDOK 1 else EnableWindow GetDlgItem hwndDlg IDOK 0 break break break We add a new case for this message But we see immediately that this nested switch state ments are getting out of hand We have to split this into a function that will handle this mes sage We change again our dialog box procedure as follows case IDCANCEL EndDialog hwndDlg 0 return 1 case IDENTRYFIELD return EntryFieldMessages hwndDlg wParam
322. flow A better version would be define Round x x lt LONG_MIN 0 5 x gt LONG MAX 0 5 error x gt 0 long x 0 5 long x 0 5 The standard library function round does this too 88 To round towards positive infinity you use define RoundUp x int x 0 5 Negative infinity is similar 1 1 Using the floating point environment The C standard specifies a type fenv_t that refers collectively to any floating point status flags and control modes supported by the implementation This environment has two special parts the floating point status flags that are set by the operations the program performs and the control flags that changes how the hardware does the operations for instance the rounding mode etc 1 1 1 The status flags The standard requires at least the following flags FE_DIVBYZERO A division by zero has occurred FE_INEXACT The last operation had to be rounded FE_INVALID An invalid operation was attempted FE_OVERFLOW The result of an operation was too big to be represented FE_UNDERFLOW The result of an operation was too small to be represented 1 Since most arithmetic operation set this flag add subtract multiply etc only the last arithmetic operation will be retained to the contrary of the other flags In addition to this standard flags lcc win provides FE_DENORMAL The result of the last operation was a denormal
323. font For example if the printer has a serifed Roman style font one of the GDI serifed Roman style fonts will appear to be very similar to the printer font However if the printer has a decorative Old English style font no corresponding screen font will typically be available The closest available match would not be very similar To have a screen font that matches the character placement of a printer font do the following e Perform the preceding seven steps to retrieve an appropriate screen font e Get the character width from the TEXTMETRIC structure returned by the EnumFonts function in step 2 above Use this information to calculate the page position of each character to be printed in the printer font e Allocate a block of memory and specify the spacing between characters Make sure that this information is in screen resolution units e Specify the address of the memory block as the IpDx parameter to ExtTextOut GDI will space the characters as listed in the array 2 22 3 How do I change the color of an edit field See page 300 2 22 4 How do draw a transparent bitmap A portion of a graphic image that does not change the contents of the screen is termed trans parent The DrawIcon function can create an image that contains transparent portions It is also possible to obtain this functionality using the BitBlt function however there are some additional steps involved The first step is to obtain the contents of the area w
324. from it The best way to pass that data is just to pass the address where it starts without having to move or make a copy of the data itself Passing an address is just passing a 32 bit number a very small amount of data If we would pass the table itself we would be forced to copy a huge amount of data into the called function what would waste machine resources The best of all worlds are references They must always point to some object there is no such a thing as an uninitialized reference Once initialized they can t point to anything else but to the object they were initialized to i e they can t be made to point to another object as normal pointers can For instance in the above expressions the pointer pa is initialized to point to the 6699 integer a but later in the program you are allowed to make the pa pointer point to 62 This has nothing to do with object oriented programming of course The word object is used here with its generic meaning 63 References aren t part of the C language standard and are in this sense an extension of lcc win They are wildly used in another related language C and the implementation of Icc win is compatible with the implementation of references of that language Pointers and references 109 another completely unrelated integer This is not possible with the reference ra It will 6699 always point to the integer a When passing an argument to a fun
325. function that would verify all allocated blocks without waiting till they are released 4 Other debugging information could be gathered for instance the line and file name the calling function a time stamp etc This information could be helpful in investigating leaks and other problems All these issues can be added to this base implementation but it would be beyond the scope of a tutorial to do it for you Start with this ideas and build further 152 C programming with Icc win32 1 31 Counting words There is no introduction to the C language without an example like this Exercise 24 C Write a program that counts the words in a given file and reports its result sorted by word frequency OK Suppose you got one assignment like that Suppose also that we use the C language defi nition of a word i e an identifier A word is a sequence of letters that begins with an under score or a letter and continues with the same set of characters or digits In principle the solution could look like this 1 Open the file and repeat for each character 2 If the character starts a word scan the word and store it Each word is stored once If it is in the table already the count is incremented for that word otherwise it is entered in the table 3 Sort the table of words by frequency 4 Print the report We start with an outline of the main procedure The emphasis when developing a program is to avoid getting distracted by t
326. functions of the C library is DBL EPSILON nextafter 1 0 2 0 1 0 For the different representations we have in the standard header lt float h gt define FLT_EPSILON 1 19209290e O7F float define DBL_EPSILON 2 2204460492503131le 16 double define LDBL_EPSILON 1 084202172485504434007452e 19L long double qfloat epsilon truncated so that it fits in this page define QFLT_EPSILON 1 09003771904865842969737513593110651 E 106 These definitions except the qfloat part are part of the C99 ANSI standard For the standard types float double and long double they should always exist in other compilers Here is a program that will find out the machine epsilon for a given floating point representa tion include lt stdio h gt int main void double float_radix 2 0 double inverse_radix 1 0 float_radix double machine_precision 1 0 double temp 1 0 machine_precision while temp 1 0 machine _ precision inverse_radix temp 1 0 machine_precision printf 17g n machine_precision 87 See http serc iisc ernet in ghoshal fpv html nodeliver or the home page of the Siddhartha Kumar Ghoshal Senior Scientific Officer at the Supercomputer Education and Research Centre Indian Insti tute of Science Bangalore 202 C programming with Icc win32 return 0 EXERCISE 2 Explain why in the above program the value of DBL_EPSILON is not the last number but the number before EXERCIS
327. g C code if expr1 0 result 0 else if expr2 0 result 0 else result 1 In a similar way we can say that the expression result exprl expr2 is equivalent to if expr1 0 result 1 else if expr2 0 result else result 1 0 1 13 30 Bitwise operators The operators amp bitwise AND bitwise exclusive or and bitwise or perform boolean operations between the bits of their arguments that must be integers long long long int short or char The operation of each of them is as follows 1 The amp AND operator yields a 1 bit if both arguments are 1 Otherwise it yields a 0 2 The exclusive or operator yields 1 if one argument is 1 and the other is zero i e it yields 1 if their arguments are different Otherwise it yields zero 3 The or operator yields 1 if either of its arguments is a 1 Otherwise it yields a zero We can use for those operators the following truth table a b a amp b a b alb 0 0 0 0 0 0 1 0 1 1 1 0 0 1 1 1 1 1 0 1 Note that this operators are normal operators i e they evaluate always their operands unlike amp amp or ll that use short circuit evaluation If we write 0O amp amp fn 67 A closer view 67 the function call will never be executed If we write 0 amp n 67 the function call will be executed even if the result is fixed from the start 1 13 31 Shift operators Shift
328. g long integer i e 64 bits We can access the 64 bit integer s low and high part as 32 bit numbers This is useful for functions returning two results in a 64 bit number Advanced windows techniques 323 pszDstFileName argv argce 1 Dst is the last argument We open the source file for reading only and make it available for other processes even if we are copying it We demand to the operating system to ensure that the file exists already hSrcFile CreateFil pszSrcFileName GENERIC_READ Source file is opened for reading only FILE_SHARE_READ Shareable 0 OPEN_EXISTING 0 0 if INVALID_HANDLE_VALUE hSrcFile printf couldn t open s n pszSrcFileName goto DONE We open the destination file for reading and writing with no other access allowed We demand the operating system to create the file if it doesn t exist Ki hDstFile CreateFile pszDstFileName GENERIC_READ GENERIC_WRITE 0 0 CREATE_ALWAYS 0 0 if INVALID_HANDLE_VALUE hDstFile printf couldn t create s n pszSrcFileName goto DONE la We need to query the OS for the size of this file We will need this information later when we create the file mapping object Note that we receive a 64 bit number splitted in two We receive a 32 bit integer containing the result s lower 32 bits and we pass to the function the address where it should put the remaining bits Well if you find this interface strange why not retu
329. g zero of the string that will be always there If it is not an absolute path we have to handle the cases where we have a path in the form of 1 00 c We find the current directory using the getcwd function and we add to it the path part of our specification for example if we had c we would add to it Then we pass this path to the PathCanonicalize function that will resolve the embed ded in any order they appear If the path was an absolute path we assume there are no embedded in it and we just copy it to the buffer that receives the path Of course in a more advanced and robust program you should check for that possibility and adding a call to PathCanonicalize is not really a big deal 4 At last we arrive to the second part of our task We have a possibly ambiguous specifica tion like c and we want to ask the system to find out all files that match We do that by calling the function _findfirst that returns either a valid search handle or 1 if it could not find any file that matches the specification If we found at least one file we start looping calling _findnext to get the next file to pro cess We give to the function that will process the file two arguments the expression that we compiled just before and the file name to process That function returns the number of matches that we add to our count When there are no more matches we are done we close the search
330. ge of sockets net bios etc etc here you will find it Windows System programming Secrets Matt Pietreck IDG Books Windows Internals Matt Pietreck Addison Wesley This books are source books for understanding how windows works and how it is built Not easy to read for beginners but indispensable for more advanced programmers 2 25 2 URLs http www catch22 net tuts A site with many good Win32 programming examples http www winprog org tutorial theForger s Win32 API Tutorial Introduction 387 Network Programming 3 1 Introduction Network programming under windows started with the windows socket implementation under windows 3 0 That implementation was a port of the sockets implementation of Unix to win dows that added some support for the asynchronous calls under the weak multitasking of the 16 bit windows implementation When windows passed to 32 bits under windows 95 the sockets implementation improved of course since a real multitasking operating system was running Based on the windows sockets implementation Microsoft released first the wininet interface later the winhttp interface The wininet interface is better for people that are concerned with some other protocols as http of course and it is a more low level interface than winhttp Of course low level is here very relative Having implemented a full FTP protocol under win dows 3 1 the wininet interface is kilometer higher than the bare win
331. general failure code This way the ErrorEnv can be always used without fearing a crash Note that I used memcpy and not just the assignment pushed_env ErrorEnv wrong since jmp_buf is declared as an array as the standard states Arrays can only be copied with memcpy or a loop assigning each member individually Note that this style of programming is sensitive to global variables Globals will not be restored to their former values and if any of the procedures in the process function modified global variables their contents will be unchanged after the longjmp include lt set jmp h gt jmp_buf ErrorEnv double global int guard void Return 0 if successful else longjmp code jmp_buf pushed_env memcpy push_env ErrorEnv sizeof jmp_buf int status setJjmp ErrorEnv global 78 9776 if status 0 process memcpy ErrorEnv pushed_env sizeof jmp_buf Here the contents of global will be either 78 9776 or 23 87 if the longjmp was taken return status int process void int error _code 0 global 23 87 if error_code long jmp ErrorEnv error_code And if you erase a file longjmp will not undelete it Do not think that longjmp is a time machine that will go to the past setimp and longjmp 87 Yet another problem to watch is the fact that if any of the global pointers pointed to an address that was later released after the longjmp their contents will
332. generator is to add jitter to the distribution of stars Variables in curvature of galactic arm try in 2 maxit maximum iteration number scale radial multiplicative scale factor cut radial cutoff f final cutoff Code loopl Do i 0 to maxit theta float i 50 r scale exp theta tan in if r gt cut then leave loopl x r cos theta 50 y r sin theta 50 call rand randx call rand randy PlotDotAt x f randx y f randy end loop2 Do i 0 to maxit 127 The resource editor has several editors specialized for each kind of resource You get a dialog box editor a menu editor a string table editor an accelerators editor and an image editor Each one is called automatically when clicking in a resource from the menu obtained with the dir button Numerical calculations in C 283 theta float i 50 theta2 float i 50 3 14 r scale exp theta2 tan in if r gt cut then leave loop2 x r cos theta 50 y r sin theta 50 call rand ndx call rand ndy PlotDotAt x f randx y f randy end ra ra This are quite clear specs Much clearer than other specs you will find in your future career as programmer So let s translate this into C We can start with the following function void DrawGalaxy HDC hDC double in int maxit double scale double cut double f double theta theta2 r x y randx randy for int
333. gers of 16 bits or 8 integers of 8 bits Lcc win describes this fact with a union typedef struct _pW char high char low _packedWord 16 bit integer typedef struct _pDW _packedWord high _packedWord low _packedDWord 32 bit integer of two 16 bit integers typedef struct _pOQWw _packedDWord high _packedDWord low _packedQWord 64 bits of two 32 bit structures typedef union _ Union Using structures 117 _packedQWord packed int dwords 2 short words 4 char bytes 8 _mmxdata This is the union of all those types Union usage is not checked by the compiler i e if you make a mistake and access the wrong member of the union this will provoke a trap or another failure at run time One way of debugging this kind of problem is to define all unions as structures during development and see where you access an invalid member When the program is fully debugged you can switch back to the union usage 1 21 Using structures Now that we know how we can define structures we can at last solve the problem we had with our character frequencies program We define a structure containing the name of the character like this typedef struct tagChars int CharacterValue int Frequency CHARS Note that here we define two things in a single statement we define a structure called tagChars with two fields and we define a typedef CHARS that will be the name of this type Within the program
334. ghly complex function We could decompose it into smaller pieces easily for example by assigning each task to a single procedure One of the first things we could do is to put the checking of the input arguments in a single procedure FILE checkargs int argc char argv FILE infile NULL if arge lt 2 printf Usage countchars lt file name gt n else infile fopen argv 1 rb if infile NULL printf File s doesn t exist n argv 1 return infile 122 C programming with Icc win32 We pass the arguments of main to our check procedure that writes the corresponding error message if appropriate and returns either an open FILE or NULL if an error was detected The calling function just tests this value and exits if something failed int main int argc char argv int count 0 FILE infile checkargs argc argv int c if infile NULL return 1 for int i 0 i lt 256 i Frequencies i CharacterValue i the rest of main The details of how the checking of the arguments is done is now away from the main line of the main function The whole function is now easier to read and the title of the piece of code that we hid away tells the reader immediately what is going on behind that function call The next step is the initializing of the Frequencies array This is common pattern that we find very often when building software most program
335. gmtime amp ltime What does this mean The function gmtime requires a pointer to a variable of type time_t We do not have a pointer so we make one on the fly by using the address of operator The printf statement uses pointer addition to skip the first 11 characters of the result of asc time That function returns a pointer to a character string To skip characters we just add up a constant 11 to that pointer effectively skipping those characters Since we want to display the 8 following characters only we pass a width argument to the s directive of printf As you know s is a directive that instructs printf to display a character string Since we give it a maximum width of 8 only the first 8 chars will be displayed We see here the construct expr vall val2 This construct evaluates first the expression in this case tstruct dstflag If the value is different than zero the return value of the expression will be the first value in this case the character string YES If the expression evaluates to zero the second value will be chosen in this case the character string NO The result of this is passed to printf as an argument The Windows system too has a lot of time related functions Here is a handy list of the most important Note that file times are kept using 64 bits in modern versions of windows i e the numbers represent the number of 100 nanosecond intervals since January first 1
336. gs sizeof szTemp 1 szTemp char szName MAX_PATH 346 C Tutorial char szDrive 3 BOOL bFound FALSE TCHAR p szTemp do Copy the drive letter into the template string removing the backslash szDrive p Look up each device name if QueryDosDevice szDrive szName sizeof szName 1 unsigned uNameLen strlen szName If greater than file name length it s not a match if uNameLen lt buflen bFound strnicmp buf szName uNameLen 0 if bFound Reconstruct pszFilename using szTemp as scratch and replace device path with our DOS path char szTempFile MAX_PATH sprintf buf s s szDrive buft tuNameLen Go to the next NULL character while ptt while bFound amp amp p at the end of the string return result int main void FILE f fopen argv 1 r char buf 1024 if getfilename f buf sizeof buf printf File is s n buf if getfilename stdin buf sizeof buf printf Stdin is s n buf return 0 2 21 22 Setting the System Time The following example sets the system time using the SetSystemTime function BOOL SetNewTime WORD hour WORD minutes SYSTEMTIME st char pc GetSystemTime amp st if st wHour hour st wMinute minutes if SetSystemTime amp st return TRUE return FALSE r Some Coding Tips 347 gets cu
337. gs up to a maximum Scan strings for characters in strncmp P 85 up strpbrk eee length specified character sets Compare strings up to a maximum strnicmp pa 1gs up strspn Find the first substring length ignoring case Compare strings using locale strcol Pa ee strstr Find a substring specific information strcpy Copy a string into another stristr Find a string ignoring case strcspn Find a substring in a string strtok Find the next token in a string strupr Convert string to upper case strdup Duplicate a string Uses malloc strlwr Convert string to lower case strrev Reverse characters in a string You will find the details in the online documentation Besides these functions in the standard C library the operating system itself provides quite a few other functions that relate to strings Besides some relicts of the 16 bit past like Istrcat and others we find really useful functions especially for UNICODE handling CharLower CharLowerBuff CharNext CharNextExA CharPrev CharPrevExA CharToOem CharToOemBuff CharUpper CharUpperBuff CompareString FoldString GetStringTypeA GetStringTypeEx GetStringTypeW IsCharAlpha Tsehar Ap ii IsCharLower IsCharUpper LoadString Numeric lstrcat Istremp Istrempi Istrcpy Istrcpyn Istrlen MultiByteToWideChar OemToChar OemToCharBuff WideCharToMultiByte wsprintf wvsprintf 1 27 The problems with C Strings After we examined how str
338. h dynamic arrays only with arrays whose dimensions are known during the compilation From the above discussion we see too that we need always an array of pointers as big as the number of rows in the array something we do not need in the case of arrays with known dimensions Obviously if you want the best of the two alternatives you can allocate a single block of mem ory for the two dimensional array and instead of using the array notation you use the pointer notation the array formula above yourself to access the array eliminating any need for increased storage You would allocate the two dimensional array like this int result malloc sizeof int NbOfRows NbOfColumns and you would access the array like this result row NbOfColumns column Note that you have to keep the dimensions of the array separately The array of pointers can be cumbersome but it gives us more flexibility We can easily add a new row to the array i e between the row 1 and 2 We just need to add a pointer after the first one and move upward the other pointers We do not have to move the data at all Not so with the shortcut that we described above There we have to move the data itself to make space for an extra row In the case of arrays defined at compile time it is impossible to do anything since the dimensions of the array are compiled in at each access by the compiler 1 13 3 1 Variable length arrays These arrays are based on the evaluat
339. hat they should be and we press the test button We see a display like this We can enter text in the entry field and pushing Cancel or OK will finish the test mode and return us to the dialog box editor Introduction to windows programming 237 OK seems to be working We save and close the dialog box editor We come back to our dia log procedure where we will use this new entry field to get some text from the user 2 1 3 The dialog box procedure You want to do many things reacting to the different events the system sends you You want to react when a button is pressed or the user writes something in an edit field You want to be able to gather all information that the user has entered in the different widgets buttons check boxes edit fields you name it To handle all those tasks the system provides you with a common entry point the dialog box procedure that should handle all events that you are interested in Here is an example static BOOL CALLBACK DialogFunc HWND hwndDlg UINT msg WPARAM wParam LPARAM 1Param switch msg case WM_INITDIALOG Event the dialog starts InitializeApp hwndDlg wParam lParam return TRUE case WM_COMMAND Event a button is pressed switch LOWORD wParam case IDOK EndDialog hwndDlg 1 return 1 case IDCANCEL EndDialog hwndDlg 0 return 1 break case WM_CLOSE Event the dialog is closed EndDialog hwndDlg 0 retu
340. he cast that transforms str from a char into an unsigned char The reason is that it could exist a bad implementation of the toupper function that would index some table using a signed char Characters above 128 would be considered negative integers what would result in a table being indexed by a negative offset with bad consequences as you may imagine How can this program fail Since we test for NULL a NULL pointer can t provoke a trap Is this a good idea Well this depends This function will not trap with NULL pointers but then the error will be detected later when other operations are done with that pointer anyway Maybe making a trap when a NULL pointer is passed to us is not that bad since it will uncover the error sooner rather than later There is a big probability that if the user of our function is calling us to trans form the string to lower case is because he she wants to use it later in a display or otherwise Avoiding a trap here only means that the trap will appear later probably making error finding more difficult Writing software means making this type of decisions over and over again Obviously this program will fail with any incorrect string i e a string that is missing the final zero byte The failure behavior of our program is quite awful in this case this program will start destroying all bytes that happen to be in the range of uppercase characters until it hits a random zero byte This means that if you
341. he details and keep the main line of the program in your head We ignore all error checking for the time being int main int argc char argv FILE f int c fopen argv 1 r open the input file c fgetc f Read the first character while c EOF Until the end of file if isWordStart c Starts a word ScanWord c f Yes Scan it c fgetc f Go on with the next character fclose f Done with the file DoReports argv 1 Print results return 0 Return with OK This would do nicely We have now just to fill the gaps Let s start with the easy ones A word we said is a sequence of _ A Z a z followed by _ A Z a z 0 9 We write a function that returns 1 if a character is the start of an identifier word int isWordStart int c if c _ return 1 if c gt a amp amp c lt z return 1 if c gt A amp amp c lt Z return 1 return 0 This function will do its job but is not really optimal We leave it like that for the time being Remember optimizations are done later not when designing the program Counting words 153 Now we go to the more difficult task of scanning a word into the computer The algorithm is simple we just keep reading characters until we find a non word char that stops our loop We use a local array in the stack that will hold until MAXIDLENGTH chars define MAXIDLENGTH 512 int
342. he integer value of entered Example ABC xA is the hexadecimal digits equivalent to ABC n The same as the x case above but with values entered as 3 octal digits Any Example The string lt octal number gt i e numbers in base 8 Note that no ABC 012 is equivalent to special character is needed after the ABC n backslash The octal digits start immediately after it Character string constants that are too long to write in a single line can be entered in two ways char a This is a long string that at the end has a backslash that allows it to go on in the next line Another way introduced with C99 is char a This is a long string written in two lines Note too that character string constants should not be modified by the program Lcc win stores all character string constants once even if they appear several times in the program text For instance if you write char a abc char b abc Both a and b will point to the SAME string and if either is modified the other will not retain the original value 1 13 3 Arrays Here are various examples for using arrays int a 45 Array of 45 elements a 0 23 Sets first element to 23 a a 0 56 Sets the 24 element to 56 a 23 56 Adds 56 to the 24 element char letters C Note that the last array letters is NOT a zero terminated character string but an array of 3 positions that is not ter
343. he translations between Coordinated Universal Time UTC and local time LocalFileTimeToFileTime Converts a local file time to a file time based on the Coordinated Universal Time UTC SetFileTime Sets the date and time that a file was created last accessed or last modified SetLocalTime Sets the current local time and date SetSystemTime Sets the current system time and date The system time is expressed in Coordinated Universal Time UTC SetSystemTimeAdjustment Tells the system to enable or disable periodic time adjustments to its time of day clock SetTimeZonel nformation Sets the current time zone parameters These parameters control translations from Coordinated Universal Time UTC to local time SystemTimeToFileTime Converts a system time to a file time SystemTimeToTzSpecificLocalTime Converts a Coordinated Universal Time UTC to a specified time zone s corresponding local time You can convert from unix time to a file time representation with the following function include lt winbase h gt include lt winnt h gt include lt time h gt void UnixTimeToFileTime time_t t LPFILETIME pft long long 11 11 Int32x32To064 t 10000000 116444736000000000 pft gt dwLowDateTime DWORD 11 162 C programming with Icc win32 pft gt dwHighDateTime 11 gt gt 32 Once the UNIX time is converted to a FILETIME structure other Windo
344. hecking suppressed for clarity FILE f fopen argv 1 r FILE out fopen argv 2 w bytesread fread buffer 1 sizeof buffer f byteswritten fwrite buffer 1 sizeof bufffer out fclose f fclose out return 0 e In this hypothetical program we establish a connection for reading from a device named in the first argument argv 1 We connect to another device named in the second argument we read from the first device we write into the second device then we close both 1 9 3 Examples For a beginner it is very important that the basic libraries for reading and writing to a stream and the mathematical functions are well known To make more concrete the general descrip tions about input output from the preceding sections we present here a compilable complete example The example is a function that will read a file counting the number of characters that appear in the file A program is defined by its specifications In this case we have a general goal that can be expressed quickly in one sentence Count the number of characters in a file Many times the specifications aren t in a written form and can be even completely ambiguous What is impor tant is that before you embark in a software construction project at least for you the specifica tions are clear include lt stdio h gt 1 int main int argc char argv 2 int count 0 chars read 3 FILE infile 4 int c 5 infi
345. hen linked with the link editor to build the final program Normally each module is written in a separate text file that contains functions or data declarations Interfaces between modules are written in header files that describe types or functions visible to several modules of the program Those files have a h extension and they come in two flavours system wide furnished with Icc win and private specific to the application you are building A function has a parameter list a body and possibly a return value The body can contain declarations for local variables i e variables activated when execution reaches the function body 3 Lisp and scheme two list oriented languages featured automatic garbage collection for decades APL and other interpreters offered this feature too Lcc win offers you the garbage collector developed by Hans Boehm 4 And today the linux kernel is written entirely in C as most operating systems 5 There is no distinction between functions and procedures in C A procedure is a function of return type void 6 Actually the startup code calls main When main returns the startup code regains control and ends the program This is explained in more detail in the technical documentation 7 Any program in any computer in any language has two main types of memory at the start The code of the program i e the sequence of machine instructions that the program will execute This section has an
346. here the bitmap will be drawn and to store this background image in a memory display context DC Mask out the area of the back ground that corresponds to the nontransparent portion of the image bitmap and mask out all transparent pixels from the image bitmap Use the XOR raster operation to merge the image bitmap into the background bitmap Finally use the BitBlt function to move the merged image to the destination DC FAQ 355 The following nine steps describe a process used to draw transparent bitmaps Create a DC to hold the image bitmap Select the image bitmap into the DC Create a memory DC to hold the final image This is the destination DC Copy the portion of the screen that will be covered by the image into the destination DC Create an AND mask that contains the mask of the colors to draw the nontransparent portions of the image To do this perform the following three steps Set the background color of the image DC to the color that will be transparent in the image Create a monochrome DC BitBlt the image into the monochrome DC This will create an AND mask of the bitmap by setting pixels that match the background color to white 1 and setting all other pixels to black 0 Use BitBlt with the SRCAND raster operation code to copy the AND mask onto the destination DC Use BitBlt with the SRCAND raster operation code to copy the inverse of the AND mask onto the image DC Use BitBlt with the SRCPAINT raster operation
347. his feature There are several reasons for this Using this representation allows memory stored numbers to be identical to numbers as used by the floating point unit Programs will give the same results even if they store intermediate results in memory Using the floating point environment 207 It simplifies the compiler and the complexity of the code generation machinery All these types can be mixed in an expression and most operators like or are defined for them with the exception of less less equal greater and greater equal You should always include the complex h standard header file when you use this type of numbers In that header file the basic keyword _Complex is replaced by just complex and it will be used here as an equivalent keyword 1 0 1 1 Complex constants They can be written in two ways include lt complex h gt double complex s 123 0 12 8i double complex m 123 0 12 8I Not case sensitive or include lt complex h gt double complex s 123 0 12 8 I Note that the first notation is not standard but used in the other compiler systems and it applies only to explicit constants Please do not assume that if you have a variable x just writing xi will transform it into a complex number When in your code you build a complex number using constants you should use the standard notation double complex w 123 45 67 89 I In this example the real part of the num
348. his function does int APIENTRY WinMain HINSTANCE hinst HINSTANCE hinstPrev LPSTR lpCmdLine int nCmdShow WNDCLASS wc A structure of type WNDCLASS memset amp wc 0 sizeof wc We set it to zero wce lpfnWndProc DefDlgProc Procedure to call for handling messages we cbWndExtra DLGWINDOWEXTRA we hInstance hinst we hCursor LoadCursor NULL IDC_ARROW wce hbrBackground HBRUSH COLOR_WINDOW 1 we lpszClassName dialog RegisterClass amp wc return DialogBox hinst MAKEINTRESOURCE IDD_MAINDIALOG NULL DLGPROC DialogFunc We see that the main job of this function is filling the structure wc a WNDCLASS structure with data and then calling the API DialogBox What is it doing We need to register a class in the window system The windows system is object oriented since it is derived from the original model of the window and desktop system developed at Xerox a system based in SmallTalk an object oriented language Note that all windows sys tems now in use maybe with the exception of the X Window system are derived from that original model The Macintosh copied it from Xerox and some people say that Microsoft cop ied it from the Macintosh In any case the concept of a class is central to windows A class of windows is a set of window objects that share a common procedure When some messages or events that concern this window are detected by the
349. ialog hwnd 0 break void 0x400000 400 hwndMain void 0x904a8 function proc _SearchDlgProc 16 parameter 1243860 A quick look at the doc of DialogBoxParazm tells us If the function fails the return value is 1 Ahh how clear Yes of course it failed But why Mystery There are no error codes other than just general failure What could be wrong Normally this 1 means that the resource indicated by the integer code could not be found I have learned that the hard way and I am writing this tutorial for you so that you learn it the easy way The most common cause of this is that you forgot to correctly give a symbolic name to your dialog We close the debugger and return to the resource editor There we open the dialog box proper ties dialog box by double clicking in the dialog box title bar and we see that we forgot to change the name of the dialog to IDM_SEARCH We correct that and we try again Filling the blanks 295 OK this looks better The dialog is showing Text Search The rest is quite trivial most of the wok was done when building the DLL Actually the dialog box is exactly the same 131 131 Newer versions of Wedit check for this Older ones aren t so sophisticated so please take care 296 C Tutorial 2 13 Using the graphical code generator As we saw before writing all that code for a simple dialog is quite a lot of work It is impor tant tha
350. ifies dialog box template name HWND hWndParent Handle to owner window DLGPROC lpDialogFunc Pointer to dialog box procedure i Non modal dialog boxes should be used with care since they are equivalent to starting another thread of execution In addition you should never forget that the user can restart the same sequence of events that led to that dialog box causing a second dialog box to appear 2 21 11 Displaying the environment variables Windows as many other operating systems maintains an environment variable block that can be queried by the program Here is a small program that will display the environment variables in the standard output include lt windows h gt include lt stdio h gt include lt stdlib h gt int main void char lpszVariable void lpvEnv Get a pointer to the environment block lpvEnv GetEnvironmentStrings if lpvEnv NULL If the returned pointer is NULL exit printf API GetEnvironmentStrings failed code d n GetLastError return EXIT_FAILURE Variable strings are separated by NULL byte and the block is terminated by a NULL byte lpszVariable char lpvEnv while lpszVariable printf ss n lpszVariable Skip to the next variable lpszVariable strlen lpszVariable 1 FreeEnvironmentStrings lpvEnv return EXIT_SUCCESS 342 C Tutorial 2 21 12 Propagating environment
351. ile hDstMap FILE_MAP_WRITE 1i0ffset HighPart 1iOffset LowPart liMapSize LowPart We use memcpy to do the actual copying memcpy pDst pSrc liMapSize LowPart UnmapViewOfFile pSrc UnmapViewOfFile pDst liBytesRemaining QuadPart liMapSize QuadPart while liBytesRemaining QuadPart gt 0 fResult SUCCESS DONE We are done Note the error treatment of this function We use gotos to reach the end of the function and here we cleanup everything Advanced windows techniques 325 if hDstMap CloseHandle hDstMap if nDstFile INVALID_HANDLE VALUE CloseHandle hDstFile if hSrcMap CloseHandle hSrcMap if hSrcFile INVALID HANDLE VALUE CloseHandle hSrcFile if fResult SUCCESS printf copying s to s failed n pszSrcFileName pszDstFileName DeleteFile pszDstFileName return fResult Summary To get a pointer to a memory mapped file do the following e Open the file with CreateFile e Create a mapping object with CreateFileMapping using the handle you receive from CreateFile e Map a portion or all of the file contents i e create a view of it with MapViewOfFile 2 18 2 Letting the user browse for a folder using the shell A common task in many programming situations is to let the user find a folder directory in the file system hierarchy When you want to search for certain i
352. ilemma is to use signal together with the setjmp longjmp facility to recover somewhere else in the program Here is an example include lt signal h gt include lt stdio h gt include lt stdlib h gt For exit include lt set jmp h gt jmp_buf jumpbuffer This function will call longjmp to reestablish a previous context assumed in the jumpbuffer global variable void traphandler int s psignal s Error long jmp jumpbuffer 1 int main void char p NULL void oldhandler int oldhandler signal SIGSEGV traphandler if oldhandler SIG_ERR printf Impossible to establish a signal handler n exit EXIT_FAILURE if setjmp jumpbuffer else p 0 signal SIGSEGV oldhandler printf Normal exit n return 0 This will print Error Segmentation fault Normal exit What happens The first time we arrive at the statement if set jmp jumpbuffer the setjmp function will return zero and we will enter the else clause There we produce a trap SIGSEGV what will raise the signal mechanism that will call the traphandler func tion In there we print the name of the signal using the standard library function psignal and then we make a longjmp that will return to the same if set jmp jumpbuffer but this time with a value of 1 Instead of getting into the else arm of the if statement we enter the branch with the
353. ime using the GetWindowRect function since we are interested in the whole surface of the status bar window not only in the size of its drawing surface We sub tract the height of the window from the height that should have the tree control and then we move it to the correct position i e filling the whole drawing surface of the window And we are done with drawing 2 10 3 Starting the scanning Now we pass to the actual task of our program We want to fill the tree control with a descrip tion of all the windows in the system A convenient way to do this is to change the New menu item into Scan and start scanning for windows when the user chooses this item To do this we add an entry into the MainWndProc_OnCommand function void MainWndProc_OnCommand HWND hwnd int id HWND hwndctl UINT codeNotify switch id case IDM_NEW BuildTree hwnd break case IDM_EXIT PostMessage hwnd WM_CLOSE 0 0 break A more complex example a clone of spy exe 275 Simple isn t it We just call BuildTree and we are done 2 10 4 Building the window tree We start with the desktop window we add it to the tree and then we call a procedure that will enumerate all child windows of a given window We have two directions to follow the child windows of a given window and the sibling windows of a given window This is true for the desktop window too Let s look at the code of BuildTree int BuildTree HWND parent
354. in a DLL to int __declspec dllexport dllexport make it visible from outside fn int Do not add the standard prologue or __declspec epilogue to the function The return int __declspec naked naked instruction and any other code should fn int be added as _asm statements defined as long long for int64 compatibility reasons with int64 big Microsoft s compiler 48 C programming with Icc win32 1 12 Extensions of Icc win type amp id expr object of the given type References must be initialized immediately after their declaration T operator T a operator opname args Redefine one of the operators like or tes a b others so that instead of doing the normal one statements operation this function is called instead Identifier will be a reference to a single int amp ra a pa will be a reference to an integer int fn int a int b 0 Default function arguments If the argument is not given in a call the compiler will fill it with the specified compile time constant int overloaded fn int int overloaded fn double Generic functions These functions have several types of arguments but the same name A closer view 49 1 13 A closer view Let s explain a bit the terms above The table gives a compressed view of C Now let s see some of the details 1 13 1 Identifiers An identifier is actually a nam
355. in an assignment 50 The relevant place in the C standard is 6 3 2 1 where the automatic type conversions are specified Except when it is the operand of the sizeof operator or the unary amp operator or is a string literal used to initialize an array an expression that has type array of type is converted to an expression with type pointer to type that points to the initial element of the array object and is not an lvalue setimp and longjmp 85 1 16 setjmp and longjmp 1 16 1 General usage This two functions implement a jump across function calls to a defined place in your program You define a place where it would be wise to come back to if an error appears in any of the procedures below this one For instance you will engage in the preparation of a buffer to send to the database or some other lengthy operation that can fail Memory can be exhausted the disk can be full yes that can still arrive specially when you get a program stuck in an infinite write loop or the user can become fed up with the waiting and closes the window etc For all those cases you devise an exit with longjmp into a previously saved context The clas sical example is given by Harbison and Steele include lt set jmp h gt jmp_buf ErrorEnv int guard void Return 0 if successful else lonjmp code int status set jmp ErrorEnv if status 0 return status error process return 0 int
356. in the editor a complex sequence of events all of them invisible to you produce an executable file Here is a short description of this so that at least you know what s happening behind the scene Wedit calls the C compiler proper This program is called Icc exe and is in the installation directory of lcc in the bin directory For instance if you installed Icc in c lcc the compiler will be inc 1lcc bin This program will read your source file and produce another file called object file that has the same name as the source file but a obj extension under windows or a o extension under 16 This has nothing to do with object oriented programming of course Hello 7 linux C supports the separate compilation model i e you can compile several source modules producing several object files and rely in the link editor IcclInk exe to build the executable Leclnk exe is the link editor or linker for short This program reads different object files library files and maybe other files and produces either an executable file or a dynamically loaded library a DLL When compiling your hello c file then the compiler produced a hello obj file and from that the linker produced a hello exe executable file The linker uses several files that are stored in the lcc lib directory to bind the executable to the system DLLs used by all programs kernel32 dll crtdll dll and many others The workings of the lcc compiler are desc
357. ings are presented in C let us apply our new knowledge The program looks ok and running it with a few files in the current directory works Let s try then H lcc examples gt freql src77 c more CRASH What s happening The problems with C Strings 133 Following the program in the debugger we see that we do not test for NULL when opening a file We correct this both in checkargs and GetNext We write a function Fopen using the same model as xmalloc if it can t open a file it will show an error message in stderr and exit the program FILE Fopen char name char mode FILE result fopen name mode if result NULL fprintf stderr Impossible to open s n name exit EXIT_FAILURE return result Ok we change all fopen into Fopen recompile and we test again H lcc examples gt freql src77 c more Impossible to open Alloc c Well this looks better but why doesn t open Alloc c Well it seems that the path is not being passed to fopen so that it tries to open the file in the current directory instead of opening it in the directory we specify in the command line One way to solve this would be to change our current directory to the directory specified in the command line and then try to open the file We could do this in checkargs since it is there where we open a file for the first time All other files will work if we change the current direc tory th
358. initialize a variable in BOTH cases of an if statement Bugs such as this are very difficult to catch later on 138 C programming with Icc win32 What will happen if the name of the file is bigger than our buffer This function will fail The fopen call will return NULL since the file name has been truncated and we will show an error telling that a truncated file name doesn t exist Is this a good behavior It depends For a technical user a long and truncated file name could be an indicator that the file name is just too long Better error reporting would be appropriate if required for instance at the start of the function a test could produce a clear message like Name too long 1 28 1 A buffer overflow in the C standard document Examples of sloppy programming abound but it was for me a surprise to discover that the C standard itself propagates this same kind of who cares attitude In the official C standard of 1999 we find the specifications of the asctime function page 341 char asctime const struct tm timeptr static const char wday_name 7 3 Bis Sun W 7 Mon W y W Tue W Wed i W Thu W y Fri W 7 W Sat W static const char mon_name 12 3 W Jan W Feb W x Mar F Apr k May W y W Jun W W Jul W a Aug 7 W Sep W P Oct P Nov 5 Dec static char result 26 sprintf result 3s 3s 3d 2d 2d 2d d n wday_name timeptr gt tm_wday mon_name timeptr gt tm_mon
359. int will make a mapping between the bitmap colors and the color we want to give to our simulated display To draw the characters we will make a memory display context where we will store the bit map of characters When we want to draw one char we will copy from the memory bitmap to the display window the portion of the bitmap that contains our character translating the colors as we go We have to take care of scrolling if necessary and many other things The purpose here is not to show you how you implement the best ever Icd display in a PC but to show the interfaces of a custom control so we will keep the logic to the bare minimum Let s see our DoPaint procedure static void DoPaint HWND hwnd 1 PAINTSTRUCT ps 2 HDC hDC BeginPaint hwnd amp ps 3 int len strlen Text 4 HBITMAP bmp oldBitmap 5 HDC dcMemory 6 COLORMAP ColorMap 4 7 int charcount 0 8 int linecount 1 9 RECT m_rect rc 10 int x y 12 ColorMap 0 from SEGM_COLORS 0 13 ColorMap 0 to PixelOnColor 14 ColorMap 1 from SEGM_COLORS 1 15 ColorMap 1 to PixelOffColor 16 ColorMap 2 from SEGM_COLORS 2 17 ColorMap 2 to PixelBackColor 18 bmp CreateMappedBitmap hInst ResourcelId 0 ColorMap 3 19 dcMemory CreateCompatibleDC hDC 20 oldBitmap SelectObject dcMemory bmp 21 HBRUSH hbBkBrush CreateSolidBrush PixelBackColor 22 GetClientRect hwnd amp m_re
360. intf to print something in the screen This time we pass to printf the following arguments Argument d s n count argv count 20 An error that happens very often to beginners is to start the loop at 1 and run it until its value is smaller or equal to the upper value If you do NOT use the loop variable for indexing an array this will work of course since the number of iterations is the same but any access to arrays using the loop index a common case will make the program access invalid memory at the end of the loop 12 C programming with Icc win32 Printf will scan its first argument It distinguishes directives introduced with a per cent sign from normal text that is outputted without any modification We have in the character string passed two directives a d and a s The first one a d means that printf will introduce at this position the character representation of a number that should also be passed as an argument Since the next argument after the string is the integer count its value will be displayed at this point The second one a s means that a character string should be introduced at this point Since the next argument is argv count the character string at the position count in the argv array will be passed to printf that will display it at this point 5 We finish the scope of the for statement with a closing brace This means the iteration definition ends here Now we are ready
361. ion void multiple void This comment will be inserted in the interface the next time you ask for the description of the function 1 10 2 Describing a file In the same context menu that appears with a right click you have another menu item that says description of file c where file c is the name of the current file This allows you to describe what the file does The editor will add automatically the name of the currently logged on user most of the time the famous administrator The output of the interface looks like this Module description Name a Micc examples regexp try c Identification Author ADMINISTRATOR Project OT Creation State This module tests the regular expressions package It is self contained and has a main function that will open a file given in the command line that is supposed to conttain several regular expressions to test If any error are discovered the results are printed to stdout Zi Module d lcc examples regexp try c Author ADMINISTRATOR Project State Creation Date An overview of the whole language 39 Description This module tests the regular expressions package It is self contained and has a main function that will open a file given in the command line that is supposed to contain several regular expressions to test If any errors are discovered the results are printed to stdout As with the other standard comment the editor will r
362. ion is updated GetArcDirection Returns the current arc direction for the specified device context Arc and rectangle functions use the arc direction Draws a line from the current position up to but not LineTo vgs including the specified point MoveToEx Updates the current position to the specified point and optionally returns the previous position PolyBezier Draws one or more B zier curves PolyBezierTo Same as PolyB zier but updates the current position PolyDraw Draws a set of line segments and B zier curves PolyLine Draws a series of line segments by connecting the points in the specified array PolyLineTo Updates current position after doing the same as PolyLine PolyPolyLine Draws multiple series of connected line segments Sets the drawing direction to be used for arc and rectangle SetArcDirection functions There are many other functions for setting color working with rectangles drawing text Tex tOut etc Explaining all that is not the point here and you are invited to read the documenta tion Summary C converts integer and other numbers to double precision when used in a double precision expression This will be done too when an argument is passed to a function When the function expects a double and you pass it an int or even a char it will be con verted to double precision by the compiler All functions that return a double result must decl
363. ion of an expression that is computed when the program is running and not when the program is being compiled Here is an example of this construct int Function int n int table n 6699 The array of integers called table has n elements This n is passed to the function as an argument so its value can t be known in advance The compiler generates code to allocate space for this array in the stack when this function is entered The storage used by the array will be freed automatically when the function exits 1 13 4 Compound literals You can use a construct similar to a cast expression to indicate the type of a composite con stant literal For instance typedef struct tagPerson char Name 75 int age Person void process Person process amp Person Mary Smith 38 54 C programming with Icc win32 This is one of the new features of C99 The literal should be enclosed in braces and it should match the expected structure This is just syntactic sugar for the following Person _ 998815544ss Mary Smith 38 process amp _998815544ss The advantage is that now you are spared that task of figuring out a name for the structure since the compiler does that for you Internally however that code represents exactly what happens inside Icc win 1 13 5 Function call syntax sqrt hypo 6 0 9 0 Calls the function hypo with two arguments and then calls the fu
364. ip SIGNATURE Overwrite the signature so that this block can t be freed again ipt 0 s ip ip int amp p s sizeof int if ip MAGIC ErrorPrintf Overwritten block size d s return ip 0 AllocatedMemory s free p 150 C programming with Icc win32 else The block has been overwritten Complain ErrorPrintf Wrong block passed to release The allocate function adds to the requested size space for 3 integers 1 The first is a magic number a signature that allows the identification of this block as a block allocated by our allocation system 2 The second is the size of the block After this two numbers the data follows 3 The data is followed by a third number that is placed at the end of the block Any memory overwrite of any block will overwrite probably this number first Since the release function check for this we will be able to detect when a block has been overwritten At any time the user can ask for the size of total allocated memory valid blocks in circula tion by querying the AllocatedMemory variable The release function accepts NULL that is ignored If the pointer passed to it is not NULL it will check that it is a valid block and that the signature is still there i e that no memory overwrites have happened during the usage of the block The global variable AllocatedMemory contains the number of bytes allocated so far This
365. is a network connection and your internet service provider has problems with the router connected to your machine or whatever There are endless reasons why hard ware can fail You can find out the reason for this using the feof and ferror functions 1 10 Commenting the source code The writing of commentaries apparently simple is when you want to do it right quite a diffi cult task Let s start with the basics Commentaries are introduced in two forms Two slashes introduce a commentary that will last until the end of the line No space should be present between the first slash and the second one A slash and an asterisk introduce a commentary that can span several lines and is only ter minated by an asterisk and a slash The same rule as above is valid here too no space should appear between the slash and the asterisk and between the asterisk and the slash to be valid comment delimiters Examples This is a one line commentary Here are ignored anyway This is a commentary that can span several lines Note that here the two slashes are ignored too This is very simple but the difficulty is not in the syntax of commentaries of course but in their content There are several rules to keep in mind Always keep the commentaries current with the code that they are supposed to comment There is nothing more frustrating than to discover that the commentary was actually mislead ing you because it wasn t u
366. ision number The size of an integer is four in Icc win and the size of a double is eight The size of this union will be eight bytes with the integer and the double precision number starting at the same memory location The union can contain either an integer or a double precision number but not the two If you store an integer in this union you should access only the integer part if you store a double you should access the double part Field access syntax is similar to structures Using the definition above we can write int main void union intfloat ifl union intfloat pIntfl amp ifl ifl i 2 pintfl gt d 2 87 First we assign to the integer part of the union an integer then we assign to the double preci sion part a double Unions are useful for storing structures that can have several different memory layouts In general we have an integer that tells us which kind of data follows then a union of several types of data Suppose the following data structures struct fileSource 65 Note that putting structure names in typedefs all uppercase is an old habit that somehow belongs to the way I learned C but is in no way required by the language Personally I find those all uppercase names clearer as a way of indicating to the reader that a user defined type and not a variable is used since I have never used an all uppercase name for a variable name Separating these names by upper lower case improves the readability
367. it and to track its consequences Do as much as you can to put the C com piler in your side by using always the corresponding header files to allow it to check every function call for correctness The compiler gives two types of errors classified according to their severity a warning when the error isn t so serious that doesn t allow the compiler to finish its task and the hard errors where the compiler doesn t generate an executable file and returns an error code to the calling environment We should keep in mind however that warnings are errors too and try to get rid from them The compiler uses a two level warning level variable In the default state many warnings aren t displayed to avoid cluttering the output They will be displayed however if you ask explicitly to raise the warning level with the option A This compiler option will make the compiler emit all the warnings it would normally suppress You call the compiler with lcc a lt filename gt or set the corresponding button in the IDE in the compiler configuration tab Errors can appear in later stages of course The linker can discover that you have used a proce dure without giving any definition for it in the program and will stop with an error Or it can discover that you have given two different definitions maybe contradictory to the same identi fier This will provoke a link time error too 32 You will probably see another display in your comp
368. it should put the results We assume that the dialog will return TRUE if the user pressed OK FALSE if the user pressed the Cancel button If the user pressed OK we search the text within the text that the editor has loaded in the func tion DoSearch How will our function CallDialog look like Here it is int CallDialog int id DLGPROC proc LPARAM parameter int r DialogBoxParam hInst MAKEINTRESOURCE id hwndMain proc parameter return ES We could have returned the value of the DialogBoxParam API immediately but I like storing function return values in local variables You never know what can happen and those values are easily read in the debugger We have to write a dialog function much like the one we wrote for our string DLL above We write a rough skeleton and leave the details for later BOOL CALLBACK SearchDlgProc HWND hwnd UINT msg WPARAM wParam LPARAM lParam switch msg case WM_INITDIALOG return TRUE case WM_CLOSE EndDialog hwnd 0 break return FALSE This does nothing it doesn t even put the text in the received parameter but what we are inter ested in here is to first ensure the dialog box shows itself Later we will refine it I develop software like this as you may have noticed I try to get a working model first a first approxi mation Then I add more things to the basic design Here we aren t so concerned about design anyway since
369. ith integer wraparound 220 Problems with integer casting 221 Octal numbers 221 Wrong assumptions with realloc 221 Be careful with overflow 221 Programming style 222 Fun with C 224 Calculating pi 224 Writing poetry 224 Tatoo 224 Bibliography 225 Chapter 2 Windows Programming 227 Introduction to windows programming 227 WinMain 230 Resources 233 The dialog box procedure 237 A more advanced dialog box procedure 240 User interface considerations 242 Libraries 245 Dynamically linked libraries DLLs 251 Using a DLL 254 A more formal approach 257 New syntax 257 Event oriented programming 257 A more advanced window 258 Customizing the wizard generated sample code 265 Making a new menu or modifying the given menu 265 Adding a dialog box 265 Drawing the window 266 Initializing or cleaning up 266 Getting mouse input 266 Getting keyboard input 267 Handling moving resizing 267 Window controls 268 Amore complex example a clone of spy exe 273 Creating the child windows 273 Moving and resizing the child windows 274 Starting the scanning 274 Building the window tree 275 Scanning the window tree 275 Review 276 Filling the status bar 278 Auxiliary procedures 279 Numerical calculations in C 282 Filling the blanks 287 Using the graphical code generator 296 Customizing controls 300 Processing the WM_CTLCOLORXXX message 300 Using the WM_DRAWITEM message 302 Building custom controls 305 The Registry 308 The structure of the registr
370. ition of the main function as before This one is as standard as the previous one but allows us to pass parameters to the program There are two arguments int argc This is an integer that in C is known as int It contains the number of arguments passed to the program plus one char argv This is an array of pointers to characters containing the actual arguments given For example if we call our program from the command line with the arguments foo and bar the argv array will contain 18 Here we will only describe the standard way of passing arguments as specified by the ANSI C standard the one Icc win uses Under the Windows operating system there is an alternative entry point called WinMain and its arguments are different than those described here See the Windows programming section later in this tutorial 19 This means that you receive the machine address of the start of an integer array where are stored the start addresses of character strings containing the actual arguments In the first position for example we will find an integer that contains the start position in RAM of a sequence of characters containing the name of the program We will see this in more detail when we handle pointers later on An overview of the standard libraries 11 argv 0 The name of the program that is running argv 1 The first argument i e foo 29 argv 2 The second argument i e bar We use a
371. ives that you use for files to open a communications port Here is the code to open COM for instance HANDLE hComm char gszPort COMI hComm CreateFile gszPort GENERIC_READ GENERIC_WRITI 0 0 OPEN_EXISTING FILE_FLAG_OVERLAPPED 0 Gl You use that handle to call ReadFile and WriteFile APIs Communications events are handled by SetCommMask that defines the events that you want to be informed about break clear to send ring rxchar and others You can change the baud rate managing the device control block Set CommSt ate etc As with network interfaces serial line programming is a black art Here is an example that is distributed with the Microsoft SDK include lt windows h gt include lt stdio h gt int main int argc char argv DCB dcb HANDLE hCom BOOL fSuccess char pcCommPort COM1 hCom CreateFile pcCommPort ENERIC_READ GENERIC_WRITE must be opened with exclusive access G 0 NULL no security attributes O 0 N PEN_EXISTING must use OPEN_EXISTING i not overlapped I 0 ULL hTemplate must be NULL for comm devices F if hCom INVALID_HANDLE_VALUE 316 C Tutorial Handle the error printf CreateFil failed with error d n GetLastError return 1 Build on the current configura
372. k In our text search dialog we could write in the edit field the last searched word for instance to avoid retyping Or we could fill a combo box with all the words the user has searched since the application started or whatever Important is that you remember that in that function all initializations for this dialog box should be done including memory allocation populating list boxes checking check buttons or other chores The second callback will be called when the user presses the OK button What do you want to do when this event happens In our example we would of course start the search or setup a set of results so that the procedure that called us will know the text to search for and possibly other data Different controls will react to different events You may want to handle some of them For instance you may want to handle the event when the user presses a key in an edit field to check input You can use the framework to generate the code that will trap that event for you and concentrate in a procedure that handles that event How would you do this Using the graphical code generator 299 You open the properties dialog of the edit control and check the Update message This will prompt the editor to generate a call to a function of yours that will handle the event The details are described in the documentation of the resource editor and will not be repeated here What is important to retain are the general principles at work
373. ktopPidl DesktopDir ShellMa ShellMa return 0 oc gt Free DesktopPidl oc gt Release At this point we are done with the pidl ShellMalloc gt Free DesktopPidl1 We do not need the allocator object any more ShellMalloc gt Release You do not need to do this if Colnitialize was already done at program startup if SUCCEEDED CoInitialize NULL if SUCCEEDED CoCreateInstance amp CLSID_ShellLink NULL CLSCTX_INPROC_SERVER amp IID_TShellLink void amp pLink pLink gt SetPath file pLink gt SetArguments args pLink gt SetShowCmd SW_SHOW if SUCCEEDED pLink gt QueryInterfac void amp pPersistFile amp IID_IPersistFile if DesktopDir strlen DesktopDir 1 strcat DesktopDir strcat DesktopDir shortcutname mbstowcs WDesktopDir DesktopDir 1 strlen DesktopDir bstr SysAllocString WDesktopDir pPersistFile gt Save bstr TRUE pPersistFile gt Release j SysFreeString bstr Error handling under windows 331 pLink gt Release CoUninitialize return 1 int main void CreateShortCut c program files lcc bin lcc exe compiler ink lcc win32 compiler As shown this shortcut will produce the output in the desktop so you will get a new short cut to an obj file n ot ve
374. l there is none left do Check for available data dwSize 0 if WinHttpQueryDataAvailable rcContext hRequest amp dwSize goto cleanup Allocate space for the buffer char pszOutBuffer malloc dwSizetl if pszOutBuffer goto cleanup Read the data ZeroMemory pszOutBuffer dwSize l if WinHttpReadData rcContext hRequest LPVOID pszOutBuffer dwSize amp dwDownloaded free pszOutBuffer goto cleanup OK Write the data The FTP protocol 393 fwrite pszOutBuffer 1 dwDownloaded rceContext OutputFile Free the memory allocated to the buffer free pszOutBuffer while dwSize gt 0 We are finished We fall through to the cleanup section 3 4 The FTP protocol The library winhttp lib that we used for implementing the HTTP GET functionality above is OK for its intended use HTTP There are however several other interesting protocols avail able to get information from the net like FTP Gopher and others We will turn ourselves to another high level library wininet lib This library with its header file wininet h implements FTP Gopher and HTTP It comes with an embedded caching schema and many other advanced features We will just use a tiny part of it the one that implements the FTP protocol suite FTP means File Transfer Protocol and is one of the oldest protocols around It is a 8 bit client server protocol able to handle any type of fil
375. l transformation In other cases there is no code emitted at all For instance in void p char p Transforming one type of pointer into another needs no code at all at run time in most imple mentations A closer view 69 1 13 34 1 When to use casts A case when casts are necessary occurs when passing arguments to a variadic function Since the type of the arguments can t be known by the compiler it is necessary to cast a value to its exact expected type double to float for example so that the arguments are converted to the exact types the variadic function expects For instance float f printf SLg n long double The printf function expects a long double format Lg We need to convert our float f into a long double to match the expectations of printf If the cast is eliminated the promoted value for a float when passed to a variadic function or to a function without prototype is double In that case printf would receive a double and would expect a long double resulting in a run time error or in bad output Another use of casts is to avoid integer division when that is not desired int a b double c c c a b Invokes integer division a double b Invokes floating point division In the first case integer division truncates the result before converting it to double precision In the second case double precision division is performed without any truncation 1 13 34 2 When not to use cas
376. ld width 4 An optional size flag expressed as one of the letters 11 1 L h hh j q t or z 5 The type specification a single character from the set a A c d e E f g G i n 0 p S U X X and 25 7L cosson TO TO T Lowe starts here width precision Conversion flag size flag 1 14 2 The conversion flags minus Value will be left justified The pad character is space 0 Use zero as pad character instead of the default space This is relevant only if a minimum field width is specified otherwise there is no padding If the data requires it the minimum width is not honored Note that the padding charac ter will be always space when padding is introduced right of the data Always add a sign either or Obviously a minus flag is always written even if this flag is not specified single Separate the digits of the formatted numbers in groups of three For instance quote 123456 becomes 123 456 This is an lcc win extension space Use either space or minus i e the is replaced by a space use a variant of the main version algorithm 1 14 2 1 The minimum field width This specifies that if the data doesn t fit the given width the pad character is inserted to increase the field If the data exceeds the field width the field will be bigger than the width set ting Numbers are written in decimal without any leading zeroes that could be misunderstood with the
377. le fopen argv 1 rb 6 c fgetc infile 7 while c EOF 8 count 9 c fgetc infile 10 printf d n count 11 return 0 30 C programming with Icc win32 1 We include the standard header stdio h again Here is the definition of a FILE structure 2 The same convention as for the args program is used here 3 We set at the start the count of the characters read to zero Note that we do this in the declaration of the variable C allows you to define an expression that will be used to initialize a variable gt 4 We use the variable infile to hold a FILE pointer Note the declaration for a pointer lt type gt identifier the type in this case is a complex structure composite type called FILE and defined in stdio h We do not use any fields of this structure we just assign to it using the functions of the standard library and so we are not concerned about the specific layout of it Note that a pointer is just the machine address of the start of that structure not the structure itself We will discuss pointers extensively later 5 We use an integer to hold the currently read character 6 We start the process of reading characters from a file first by opening it This operation establishes a link between the data area of your hard disk and the FILE variable We pass to the function fopen an argument list separated by commas containing two things the name o
378. le ferror Returns true when there was an error when reading from the device fputs Puts a string in a file fread Reads from a file a specified amount of data into a buffer freopen Reassigns a file pointer fgetc Reads one character from a stream fscanf Reads data from a file using a given data format fsetpos Assigns the file pointer the current position fseek Moves the current position relative to the start of the file to the end of the file or relative to the current position ftell returns the current position fwrite Writes a buffer into a file tmpnam Returns a temporary file name unlink Erases a file remove Erases a file rename Renames a file rewind Repositions the file pointer to the beginning of a file setbuf Controls file buffering ungetc Pushes a character back into a file 1 9 1 Predefined devices To establish a connection with a device we open the file that represents it There are three devices always open that represent the basic devices that the language assumes 1 The standard input device or stdin This device is normally associated with the keyboard at the start of the program 2 The standard output device or stdout This device is normally associated with the computer screen in text mode 3 The standard error device or stderr that in most cases is also associated with the computer screen Other devices that can be added or deleted from the set of devices the program can communi cate with
379. leDC lpdis gt hDC hbmpOld SelectObject hdcMem hbmpPicture BitBlt lpdis gt hDc lpdis gt rcItem left lpdis gt rcItem top lpdis gt rcItem right lpdis gt rcItem left lpdis gt rcItem bottom lpdis gt rcItem top hdcMem 0 0 SRCCOPY We are done with our memory DC Clean up SelectObject hdcMem hbmpOld DeleteDC hdcMem Now we retrieve the text for this line SendMessage lpdis gt hwndItem LB_GETTEXT lpdis gt itemID LPARAM tchBuffer How big is the text of this item GetTextMetrics lpdis gt hDC amp tm Vertically center the text y lpdis gt rcItem bottom lpdis gt rcItem top tm tmHeight 2 Send the text to the screen 6 pixels after the bitmap TextOut lpdis gt hDC XBITMAP 6 y tchBuffer strlen tchBuffer Is the item selected if lpdis gt itemState amp ODS_SELECTED Yes Invert the whole rectangle image text to signal the selection BitBlt lpdis gt hDCc lpdis gt rcItem left lpdis gt rcItem top lpdis gt rcItem right lpdis gt rcItem left lpdis gt rcItem bottom lpdis gt rcItem top lpdis gt hDC 0 0 PATINVERT break Do nothing if we gain or lose the focus This is a laxist view but it works case ODA_FOCUS break return TRUE And after all this work here it is Building custom controls 305 Dialog Title crayon essecocsccesosossosesosoccsesesocossesososossesce
380. letely scanned We close and shut down i fclose f1 if f1 f2 fclose 2 return 0 How can this program fail Well there are obvious bugs in this program Before reading the answer try to see if you can see them What is important here is that you learn how to spot bugs and that is a matter of log ical thinking and a bit of effort Solution will be in the next page But just try to find those bugs yourself Before that bug however we see this lines in there if f2 f1 amp amp fgets buf2 MAXLINELEN f2 else printf s n buf1 If f1 is different from f2 we have two different files and file two is shorter than file one that if statement will fail after n2 lines and the else portion will be executed provoking the dupli cation of the contents of the corresponding line of file one To test this we create two test files filel and file2 their contents are Filel File 1 line 1 File 1 line 2 File 1 line 3 File 1 line 4 File 1 line 5 File 1 line 6 File 1 line 7 File 1 line 8 File2 File 2 line 1 File 2 line 2 File 2 line 3 File 2 line 4 We call our paste program with that data and we obtain D lec test gt paste fileli file2 i i File 2 File 1 Line 1 2 Line 1 File 1 Line 2 File 2 Line 2 File 1 Line 3 File 2 Line 3 File i Line 4 Fil Line 4 File 1 Line 5 Ba 1 Line File 1 Line 6 a 6 File 1 Line 1 7 File 1 Line 8 al 8 D lcc test gt 96 C pr
381. lication conforms to the interface rules of the Service Control Manager SCM A user through the Services control panel applet can start it automatically at system boot or by an application that uses the service functions Services can execute even when no user is logged on to the system 2 17 14 Terminal Services When a user logs on to a Terminal Services enabled computer a session is started for the user Each session is identified by a unique session ID Because each logon to a Terminal Services client receives a separate session ID the user experience is similar to being logged on to mul tiple computers at the same time for example an office computer and a home computer The console session on the Terminal Server is assigned the session ID 0 The Remote Desktop Protocol RDP provides remote display and input capabilities over net work connections for Windows based applications running on a server RDP is designed to support different types of network topologies and multiple LAN protocols On the server RDP uses its own video driver to render display output by constructing the ren dering information into network packets using RDP protocol and sending them over the net work to the client On the client RDP receives rendering data and interprets the packets into corresponding graphics device interface API calls For the input path client mouse and key board events are redirected from the client to the server On the server RDP uses its
382. lient handle retrieved when the mailslot is opened for a write operation applications can easily implement a simple message passing facility within a domain e Pipes Conceptually a pipe has two ends A one way pipe allows the process at one end to write to the pipe and allows the process at the other end to read from the pipe A two way or duplex pipe allows a process to read and write from its end of the pipe e Memory mapped files can be used as a global shared memory buffer 2 17 8 Mail The Messaging API MAPI allows you to program your messaging application or to include this functionality into your application in a vendor independent way so that you can change the underlying message system without changing your program 2 17 9 Multimedia Audio You can use Mixers MIDI and waveform audio using MCI DirectSound offers a more advanced sound interface Input devices You can use the joystick precise timers and multimedia file input output Video Use AVI files to store video sequences or to capture video information using a simple message based interface 2 17 10 Network Windows Sockets provides you will all necessary functions to establish connections over a TCP IP network The TCPIP subsystem even supports other protocols than TCPIP itself But whole books have been written about this so here I will only point you to the one I used when writing network programs Ralph Davis Windows NT Network programming from Ad
383. like this Drive Capacity Available Used Free Cry 6 292 303 872 2 365 452 288 3 926 851 584 37 59 D 10 487 197 696 3 563 794 432 6 923 403 264 33 98 E 31 453 437 952 17 499 627 520 13 953 810 432 55 64 F 15 726 731 264 10 327 638 016 5 399 093 248 65 67 H 569 366 528 0 569 366 528 0 00 EEN 31 790 673 920 27 672 530 944 4 118 142 976 87 05 350 C Tutorial Total 96 319 711 232 61 429 043 200 34 890 668 032 63 78 Since it doesn t check if a drive is a CD drive drive H is listed and it has obviously 0 bytes available since it is read only 2 21 27 Mounting and unmounting volumes in NTFS 5 0 The windows file system allows you to mount disk drive in another directory and see the contents of the drive as if they were subdirectories of the directory where the drive is mounted Suppose for instance that you make a directory C mnt and in this directory you make a sub directory called cdrom Using the utility below you can mount the CDROM drive under the c mnt cdrom directory and you will see the contents of the cdrom drive in c mnt cdrom 2 21 27 1 Mount include lt windows h gt include lt stdio h gt define BUFSIZE MAX PATH int main int argc char argv BOOL bFlag char Buf BUFSIZE temporary buffer for volume name char buf1l BUFSIZE temporary buffer for volume name DWORD nl flags char fsname 512 if argc 3 printf Usage mount lt directory g
384. low you to see a disk file as a section of RAM The difference between the disk and the RAM disappears You can just seek to a desired position by incre menting a pointer as you would do if you had read the whole file into RAM but more effi ciently It is the operating system that takes care of accessing the disk when needed When you close the connection the operating system handles the clean up Here is a small utility that copies a source disk file to a destination using memory mapped files int main int argc char argv int fResult FAILURE ULARGE_INTEGER liSrcFileSize Seel liBytesRemaining liMapSize 1ioffset HANDLE hSrcFile INVALID HANDLE VALUE hDstFile INVALID_HANDLE_ VALUE hSrcMap 0 hDstMap 0 BYTE pSrce 0 pDst 0 char pszSrcFileName 0 pszDstFileName 0 if argc 3 test if two arguments are given in the command line printf usage copyfile lt srcfile gt lt dstfile gt n return FAILURE r pszSrcFileName argv argc 2 Src is second to last argument 135 ULARGE_INTEGER is defined in the windows headers like this typedef union _ULARGE_INTEGER struct DWORD LowPart DWORD HighPart long long QuadPart ULARGE_INTEGER PULARGE_INTEGER The union has two members a anonymous one with two 32 bit integers and another with a lon
385. lt icon we hIcon LoadIcon NULL IDI_APPLICATION if RegisterClass amp wc return 0 TODO Call module specific initialization routines here return 1 The style of the window used is a combination of integer constants like CS_HREDRAW and others combined using the OR operator the vertical bar What does this mean This is a standard way of using bit flags in C If you go to the definition of CS_HREDRAW right click in that name and choose the Goto definition option you will see that the value is 2 Other constants like CS_DBLCLKS have a value of 8 All those numbers are a power of two Well a power of two by definition will always have a single bit set All other bits will be zero If you OR those numbers with each other you will obtain a number that has the bits set that correspond to the different values used In our case this statement is equivalent to we style 2 1 8 8 ored with 1 is 1 0 0 1 ored with 2 is 1 O 1 1 what is equal to 11 in decimal notation This is a very common way of using flags in C Now if you want to know if this window is a window that answers to double clicks you just have to query the corresponding bit in the style integer to get your answer You do this with the following construct if wc style amp CS_DBLCLKS We test in this if expression if the value of the style integer ANDed with 8 is different than zero Since CS_DBLCLKS is a pow
386. lyst one who uses a computer to carry out numerical computations must have a method of bounding estimating and controlling both the round off error at each numerical step as well as the total round off error What do we want from the representation of numbers then 1 The grid points should be as dense as possible 2 The range the span between the smallest and the largest number should be as wide as possible 3 The number of bits used should be as small as possible Numerical programming 193 4 The rules of arithmetic should be mimicked as closely as possible 5 The rules should be such that they can be implemented in hard wired computer logic Note that all those requirements are completely contradictory If we want a dense representa tion we have to use more bits If we increase the range we have to thin the spacing between numbers etc 1 37 1 Floating point formats In Icc win we have a plethora of numeric types ranging from the smallest single precision for mat to the bignum indefinite precision numbers All the numeric types including the complex numbers type but excluding the bignums are based in different floating point formats In this formats a number is represented by its sign an exponent and a fraction Because the size and number of registers that any computer can have is limited only a subset of the real number continuum can be used in the calculations The floating point formats are an approximation of
387. m Device I O Manage all kind of cards with DevicelOControl Dynamically linked Yes I know It is hot in DLL Hell But at least you get separate modules using binary interfaces that can be replaced one by one This can lead to confusion but it is inherent in the method Files The disk is spinning anyway Use it File Systems Graphics Journaling file systems NTFS FAT32 As you like it Windows are graphical objects The GDI machinery allows you to draw simple objects with lines or regions but you can go to higher dimensions with DirectX or OpenGl Handles and Objects Objects that the system manages windows files threads and many others are described by a numerical identifier A handle to the object Hooks Install yourself in the middle of the message queue and hear what is being passed around you receive the messages before any other window receives them Inter Process Com Client Server and many other forms of organizing applications are munications available You have all the primitives to do any kind of architecture Synchronization pipes mailslots you name it Mail Send receive mail messages using the Messaging API Multimedia Sound video input devices 314 C Tutorial Network Yes TCP IP Send data through the wire develop your own protocol on top of the basic stuff You have all the tools in here Virtual memory Use those megabytes They
388. main menu The property sheet is just a set of dialog boxes that will be displayed by windows in a special way Each dialog box has an associated function that handles the messages to it from the child controls or from the property sheet displaying software The logic of this functions is very similar to the normal dialog box functions BOOL CALLBACK DlgProc HWND hwnd UINT msg WPARAM wParam LPARAM lParam NMHDR pnmhdr switch msg case WM_INITDLG Initialize the dialog box here This is exactly the same as in a normal dialog box procedure NOTE This will only be called if the user selects the page that this dialog box handles Otherwise the whole dialog box procedure is never called break case WM_NOTIFY pnmhdr NMHDR 1Param switch pnmhdr gt code case PSN_APPLY Here we should handle things as if the OK button was pressed If we return PSNRET_NOERROR we inform windows that the changes made are OK We can return PSNRET_INVALID to disallow the closing of the property sheet if any changes are incorrect In that case the focus would be assigned to this page Or we can return PSNRET_INVALID_ NOCHANGEPAGE to leave the focus where it is AND not discarding the property sheet return PSNRET_NOERROR case WM_COMMAND 380 C Tutorial When designing the dialog boxes of your property sheet keep in mind that all dialog boxes should have the same size Windows will adjust
389. ment any kind of numbers you would like to design it is fully general Just look at qfloat h and see what would happen with qfloat being any other number type you want Note too that nothing has changed about C There are no classes or any other underlying con text and you are free to build the context you wish as always C has been 1 36 2 References References are a special kind of pointers that are always dereferenced when used When you declare a reference you must declare immediately the object they point to There are no invalid references since they can t be assigned Once a reference is declared and initialized you can t reassign them to another object They are safer pointers than normal pointers since they are guaranteed correct unless the object they point to is destroyed of course References are initialized with the construct int a int amp pa a The pa variable is a reference to an integer an int amp and it is immediately initialized to point to the integer a Note that you do not have to take the address of a but just put its name The compiler takes the address Again here is a short pointer only A complete description is found in the user manual 1 36 3 Generic functions You can declare a function that receives several types of arguments i e a generic function by using the overloaded markert Suppose a function that receives as arguments a qfloat or a double int o
390. ments returning a pointer to a constant pointer to char Now let s see this 28 Machine addresses are just integers of course For instance if you have a machine with 128MB of memory you have 134 217 728 memory locations They could be numbered from zero up but Windows uses a more sophisticated numbering schema called Virtual memory 29 Deep C secrets Peter van der Linden ISBN 0 13 177429 8 Declarations and definitions 23 char 3j 20 Again we start with j is a pointer to At the right is an expression in brackets so we apply 2 B 2 to get j is a pointer to an array of 20 Yes what We continue at the left and see char Done j is a pointer to an array of 20 chars Note that we use the declaration in the same form without the identifier when making a cast j char 20 malloc sizeof j We see in bold and enclosed in parentheses a cast the same as in the declaration but without the identifier jJ 1 7 2 Function declaration A declaration of a function specifies e The return type of the function i e the kind of result value it produces if any e Its name e The types of each argument if any The general form is lt type gt lt Name gt lt type of arg 1 gt lt type of arg N gt double sqrt double Note that an identifier can be added to the declaration but its presence is optional We can write double sqrt double x 66 99 if we want to but th
391. message to the procedure indicated in the win dow class And that is it We loop and loop and loop until we eventually get a WM_QUIT that provokes that GetMessage returns FALSE and the while loop is finished 7 Wow Finished We have hardly started What is interesting now is that we have a skeleton to play with We will show in the next sections how we add things like a dialog box etc Summary Windows programming looks intimidating at first But it is just the looks Before we go on however as promised let s look in more details to how flags are set unset in C Flags are integers where each bit is assigned a predefined meaning Usually with a pre processor define statement powers of two are assigned a symbolic meaning like in the case of CS_DBLCLKS above In a 32 bit integer we can stuff 32 of those We test those flags with 121 Never forget this local variables do NOT retain their value from one call of the function to the next one 264 C Tutorial if flag amp CONSTANT we set them with flag CONSTANT we unset them with flag amp CONSTANT This last statement needs further explanations We use the AND operator with the complement of the constant Since those constants have only one bit set the complement of the constant is an integer with all the bits turned into ones except the bit that we want to unset We AND that with our flag integer since all bits but the one we want to set to ze
392. minated by a zero byte 52 C programming with Icc win32 Multidimensional arrays are indexed like this int tab 2 3 tab 1 2 7 A table of 2 rows and three columns is declared Then we assign 7 to the second row third column Remember arrays indexes start with zero Note that when you index a two dimensional array with only one index you obtain a pointer to the start of the indicated row int p tab 1 Now p contains the address of the start of the second column Arrays in C are stored in row major order i e the array is a contiguous piece of memory and the rows of the array are stored one after the other The individual array members are accessed with a simple formula x i j x i n j where n is the row size of the array x It is evident from this formula that the compiler treats differently a two dimensional array from a one dimensional one because it needs one more 66 99 piece of information to access the two dimensional one the size of each row n in this case How does the compiler know this value From the declaration of the array of course When the compiler parses a declaration like int tab 5 6 The last number 6 is the size of each row and is all the information the compiler needs when compiling each array access Since arrays are passed to functions as pointers when you pass a two dimensional array it is necessary to pass this information too for instance by leaving empty th
393. mmers The basic problem is that the human mind doesn t work like a machine and here we are ask ing people i e programmers to be like machines and keep book exactly of all the many small pieces of RAM a program uses during its lifetime without ever making a mistake But there is a solution that I have implemented in Icc win Lcc win comes with an automatic memory manager also called garbage collector in the literature written by Hans Boehm This automatic memory manager will do what you should do but do not want to do take care of all the pieces of RAM for you Using the automatic memory manager you just allocate memory with GC_malloc instead of allocating it with malloc The signature i e the result type and type of arguments is the same as malloc so by just replacing all malloc by GC_malloc in your program you can benefit of the automatic memory manager without writing any new line of code The memory manager works by inspecting regularly your whole heap and stack address space and checking if there is anywhere a reference to the memory it manages If it doesn t find any references to a piece of memory it will mark that memory as free and recycle it It is a very simple schema taken to almost perfection by several years of work from the part of the authors To use the memory manager you should add the gc lib library to your link statement or indi cate that library in the IDE in the linker configuration tab 73 Memory
394. n exits After that function exits the contents of all those memory locations containing local variables are undefined and the function is returning a pointer to memory that will be freed and recycled immediately Of course the memory location itself will not disappear but the contents of it will be reassigned to something else maybe another function maybe another local variable nobody knows A pointer that is not initialized or that points to an object that has disappeared is a dangling pointer and it is the nightmare of any C programmer The bugs produced by dangling pointers are very difficult to find since they depend on whether the pointers destroy or not some other object This programs tend to work with small inputs but will crash mysteriously with com plex and big inputs The reason is that in a more complex environment object recycling is done more often what means that the memory locations referenced by the dangling pointers are more likely used by another object 1 15 1 Operations with pointers The most common usage of a pointer is of course the dereferencing operation i e the oper ator gt or the unary This operations consist of reading the contents of a pointer and using the memory address thus retrieved either fetch the data stored at that place or at some displacement from that place For instance when we use a pointer to the person structure above the operation struct person pJo
395. n octal constant consists of the prefix 0 optionally followed by a sequence of the digits 0 through 7 only A hexadecimal con stant consists of the prefix Ox or 0X followed by a sequence of the decimal digits and the let ters a or A through f or F with values 10 through 15 respectively Here are various examples of integer constants 12345 integer constant decimal 0777 octal for 511 decimal OxF98A hexa for 63882 decimal Result type is unsigned 12345L long integer constant 2634455LL long long integer constant 2634455164 long long integer Microsoft notation 5488UL unsigned long constant 5488 548ULL unsigned long long constant 548 1 13 2 3 Floating constants For floating constants the convention is either to use a decimal point 1230 0 or scientific notation in the form of 1 23e3 They can have the suffix F or f to mean that they are float constants and not double constants as it is implicitly assumed when they have no suffix 66 99 A suffix of T or L means long double constant A suffix of q or Q means a qfloat The default format without any suffix is double This is important since it can be the source of bugs very difficult to find For instance long double d 1e800 The dynamic range of a long double is big enough to accept this value but since the program mer has forgotten the L the number will be read in double precision Since a double precision number c
396. n the debugger to track memory accounting bugs Advantages 1 Program logic is simplified and freed from the chores of keeping track of memory blocks 148 C programming with Icc win32 2 The program uses no more memory than needed since blocks no longer in use are recycled Drawbacks 1 It requires strict alignment of pointers in addresses multiple of four Normally this is ensured by the compiler but under certain packing conditions compilation option Zp1 the following layout could be disastrous pragma pack 1 struct short a char ptr s The pointer ptr will NOT be aligned in a memory address multiple of four and it will not be seen by the collector because the alignment directive instructs the compiler to pack structure members 2 You are supposed to store the pointers in memory accessible to the collector If you store pointers to memory allocated by the collector in files for instance or in the windows extra bytes structure maintained by the OS the collector will not see them and it will consider the memory they point to as free releasing them again to the application when new requests are done 3 Whenever a full gc is done a full scan of the stack and the heap a noticeable stop in program activity can be perceived by the user In normal applications this can take a bit less than a second in large memory pools The collector tries to improve this by doing small partial collections each time a call
397. n the user is clicking it is surely not moving the mouse at super sonic speeds Map the coordinates we received into the coordinates of the tree window Ask the tree control if there is an item under this coordinates If there is none we stop Now we have a tree item We need to know which window is associated with this item so that we can query the window for more information Since we have left in each item the window handle it is displaying we retrieve this information We hide the details of how we do this ina subroutine Get TreeItemInfo that returns us the window handle A more complex example a clone of spy exe 279 Using that window handle we call another function that will display the info in the status bar We pass all messages to the default window procedure this is a non intrusive approach The tree control could use our notifications for something We just need to do an action when this event happens but we want to disturb as little as possible the whole environment 2 10 8 Auxiliary procedures To retrieve our window handle from a tree item we do the following static HWND GetTreeItemInfo HWND hwndTree HTREEITEM hti TV_ITEM tvi memset amp tvi 0 sizeof TV_ITEM tvi mask TVIF_PARAM tvi hItem hti TreeView_GetItem hwndTree amp tvi return HWND tvi lParam As you can see it is just a matter of filling a structure and querying the control for the
398. n32 wanmning text Writes the text of a warning message This is an extension of lcc win but other compilers for instance gcc support it too warning MACHINE macro undefined If a appears at the end of a line just conditionally include or not code for Icc win before the newline character the line and the following line will be joined by this is a comment the preprocessor and the character will be eliminated LINE Replace this token by the current line printf error line d n a number __LINE__ FILE Replace this token by the current file printf error file s n aoe name __ FILE func Replace this token by the name of the printf fn s n _ func__ mae current function being compiled __STDC__ Defined as 1 if __STDC__ Defined as 1 This allows you to _LCC__ if __Lcc 1 The parentheses ensure the correct evaluation of the macro 2 The different pragma directives of lcc win are explained in the user s manual 1 11 4 Windows specific defined symbols WIN32 defined as 1 if WIN32 _WIN32 defined as 1 if _WIN32 WINVER Evaluates to the version of windows you ee SaaS Se are running Evaluates to the version of the internet _WIN32_1E explorer software installed in your if _WIN32_IE gt 0x500 system 1 11 5 Structured exception handling try protected block Introduces a
399. nPaint hwnd amp ps Code for painting using the HDC goes here EndPaint hwnd amp ps break You use the API BeginPaint to inform windows that you are going to update the window Win dows gives you information about the invalid rectangles of the window in the PAINTSTRUCT area You pass to windows the address of such an area and the handle to your window The result of BeginPaint is an HDC a Handle to a Device Context that is required by most drawing primitives like TextOut LineTo etc When you are finished you call EndPaint to inform windows that this window is updated To draw text you use Text Out or DrawText Note that under windows there is no auto matic scrolling You have to program that yourself or use a multi line edit control 2 8 4 Initializing or cleaning up You can write your initialization code when handling the WM_CREATE message This mes sage is sent only once when the window is created To cleanup you can rely on the WM_CLOSE message or better the WM_DESTROY message Those will be sent when the window is closed destroyed Note that you are not forced to close the window when you receive the WM_CLOSE message Even if this is not recommended you can handle this mes sage and avoid passing it to the DefWndProc procedure In this case the window is not destroyed Another thing is when you receive the WM_DESTROY message There you are just being informed that your window is going to be dest
400. nableWindow GetDlgItem hDlg IDOK 0 SetFocus GetDlgItem hDlg IDENTRYFIELD return 1 lt A HFONT is a font handle i e an integer that represents a font for windows We get that integer using the GetStockObject API This function receives an integer code indicating which 110 Now is a good time to read the documentation for that API It will not be repeated here User interface considerations 243 object we are interested in and returns it There are several types of object we can get from it fonts brushes pens etc Yet another point missing in our dialog box is a correct title or prompt The title of our dialog is now just dialog This tells the user nothing at all A friendlier interface would tell the user what data the software is expecting from him her We could change the title of the dialog to a more meaningful string The program calling our dialog procedure could give this string as a parameter to the dialog box Dialog boxes can receive parameters as any other procedure They receive them in the parameters passed to the WM_INITDIALOG message A closer look to the documentation of the WM_INITDIALOG message tell us that the Param message parameter contains for the WM_INITDIALOG 32 bits of data passed in the last parameter of an API called DialogBoxParam We have to modify our calling sequence to the dialog and instead of using DialogBox we use the DialogBo
401. nction BOOL SetFileToCurrentTime HANDLE hFile FILETIME ft SYSTEMTIME st BOOL f GetSystemTime amp st gets current time SystemTimeToFileTime amp st amp ft converts to file time format f SetFileTime hFile sets last write time for file LPFILETIME NULL LPFILETIME NULL amp ft return f 2 21 25 Converting from GMT UTC time to local time The system uses Universal Coordinated Time or UTC based time internally Applications gen erally display the local time or the date and time of day for the current time zone However a developer occasionally may need to programmatically convert from UTC previously referred to as Greenwich Mean time or GMT time to local time This conversion can be done like this FILETIME FileTime LocalFileTime SYSTEMTIME UTCTime LocalTime SystemTimeToFileTime amp UTCTIme amp FileTime FileTimeToLocalFileTime amp Fil ime amp LocalFileTime FileTimeToSystemTime amp LocalFileTime amp LocalTime 2 21 26 Some Coding Tips 349 Displaying the amount of disk space for each drive finclude lt windows h gt include lt stdio h gt This program will loop through all drives in the system and will print the capacity of each drive the number of bytes free used and the percentage free At the end
402. nction sqrt with the result of hypo An argument may be an expression of any object type In preparing for the call to a function the arguments are evaluated and each parameter is assigned the value of the corresponding argument A function may change the values of its parameters but these changes cannot affect the values of the arguments On the other hand it is possible to pass a pointer to an object and the func tion may change the value of the object pointed to A parameter declared to have array or function type is converted to a parameter with a pointer type The order of evaluation of the actual arguments and sub expressions within the actual argu ments is unspecified For instance fn g h m Here the order of the calls to the functions g h and m is unspecified The syntax for function pointers is the same as for a normal function call It is not needed to dereference a pointer to a function For instance int main void int fn int fn 7 fn 7 Both calls will work If the called function has a prototype the arguments are implicitly converted to the types of the corresponding parameters when possible When this conversion fails Ilcc win issues an error and compilation fails Other compilers may have different behavior When a function has no prototype or when a function has a variable length argument list for each argument the default argument promotions apply The integer p
403. nction would need some changes too LIST Insert LIST list LIST element LIST tmp if list NULL return NULL if list element return list tmp list gt Next list gt Next element if element element gt Next tmp element gt Previous list if tmp tmp gt Previous element return list Note that we can implement a Previous function with single linked lists too Given a pointer to the start of the list and an element of it we can write a Previous function like this LIST Previous LIST root LIST element if root NULL return NULL while root amp amp root gt Next element root root gt Next return root 166 C programming with Icc win32 Circular lists are useful too We keep a pointer to a special member of the list to avoid infinite loops In general we stop when we arrive at the head of the list Wedit uses this data structure to implement a circular double linked list of text lines In an editor reaching the previous line by starting at the first line and searching and searching would be too slow Wedit needs a dou ble linked list and a circular list makes an operation like wrapping around easier when search ing 1 33 2 Hash tables A hash table is a table of lists Each element in a hash table is the head of a list of element that happen to have the same hash code or key To add an element into a hash table we construct from the data stored in the eleme
404. nd many others like isspace or isdigit We need to include the stdio h header file too since it contains the definition for NULL 54 This convention is used in the library function Actually it is a quite bad interface since the return value doesn t give any new information to the user besides the expected side effect of transforming the given string A better return value would be the number of changed characters for instance that would allow the caller to know if a transformation was done at all or the length of the string or several others But let s implement this function as it is specified in the standard library Many times you will see that even if it is obvious that software must be changed the consequences of a change are so vast that nobody wants to assume it and we get stuck with software for compatibility reasons Here is yet another example Simple programs 93 The first thing we do is to test if the given pointer is NULL If it is we return NULL Then we start our loop that will span the entire string The construction while p tests if the con tents of the character pointer p is different than zero If this is the case we transform it into a lower case one We increment our pointer to point to the next character and we restart the loop When the loop finishes because we hit the zero byte that terminates the string we stop and return the saved position of the start of the string Note t
405. nd of the listbox Notice that windows does not destroy this object You should destroy it when the dialog box finishes Creating and destroying the brush that you should return is cumbersome If you are not inter ested in modifying the background you can use the API GetStockObject returning the han dle of the white brush like this return GetStockObject WHITE_BRUSH Objects created with GetStockObejct do not need to be destroyed so you spare yourself the job of creating and destroying the brush The code would look like this BOOL WINAPI MyDlgProc HWND hwnd UINT msg WPARAM wParam LPARAM lParam HDC hDC COLORREF oldcolor switch msg case WM_CTLCOLORLISTBOX hDC HDC wParam color RGB 192 0 0 red color SetTextColor hDC color return GetStockObject WHITE_BRUSH Customizing controls 301 If you want to return another brush than white you should handle the WM_INITDIALOG message to create the brush and the WM_NCDESTROY message to destroy the brush you created to avoid memory leaks In this case the above example should be augmented with BOOL WINAPI MyDlgProc HWND hwnd UINT msg WPARAM wParam LPARAM lParam HDC hDC COLORREF oldcolor static HBRUSH hBrush switch msg case WM_INITDIALOG hBrush CreateSolidBrush BK_COLOR other initializations go here case WM_CTLCOLORLISTBOX hDC HDC wParam color RGB 192 0 0 ced color SetTextColor hDC
406. nd precision of the different formats let s try this simple program It calculates the fac torial of its argument and it is not very efficient since it will repeat all calculations at each time include lt stdio h gt include lt math h gt float factf float f float result 1 0 while f gt 0 result f if isfinitef f break f return result int main void float ff 1 0f fctf 1 0 196 C programming with Icc win32 while 1 ff factf fctf if isfinitef ff break printf 10 0 40 21g n fctf fctft t printf Max factorial is g n fctf 1 return 0 We start with the smallest format the float format We test for overflow with the standard function is_finitef that returns 1 if its float argument is a valid floating point number zero oth erwise We know that our fact function will overflow and produce a NAN Not A Num ber after some iterations and we rely on this to stop the infinite loop We obtain the following output 1 1 2 2 3 6 4 24 5 120 6 720 7 5040 8 40320 9 362880 10 3628800 11 39916800 12 479001600 13 6227020800 14 87178289152 15 1307674279936 16 20922788478976 17 355687414628352 18 6402374067290112 19 121645096004222980 20 2432902298041581600 21 51090945235216237000 22 1 124000724806013e 021 23 2 5852017444594486e 022 24 6 204483105838 766e 023 25 1 5
407. nd the request if WinHttpSendRequest rcContext hRequest WINHTTP_NO_ADDITIONAL_HEADERS 0 WINHTTP_NO_REQUEST_DATA 0 0 0 goto cleanup We wait for the answer if WinHttpReceiveResponse rcContext hRequest 0 goto cleanup We are now ready to query the headers of the resource we are tryingt to obtain The reason is simple if our routine received a request for an inexistent resource many servers will send data anyway containing some HTML that will show the famous page Unable to find server or similar We surely do not want to get that so we have to scan the headers to see if we get a 404 the http error for indicating that the resource is unavailable We do not know how long the headers can be We first query the length of the buffers allocate memory then we make the request to get the actual header data dwSize 0 WinHttpQueryHeaders rcContext hRequest WINHTTP_QUERY_RAW_HEADERS_CRLF WINHTTP_HEADER_NAMFE_ BY INDEX NULL amp dwSize WINHTTP_NO_HEADER_INDEX if GetLastError ERROR_INSUFFICIENT_BUFFER goto cleanup dwSizet count the trailing zero swzHeaders malloc dwSize sizeof wchar_t szHeaders malloc dwSize if swzHeaders NULL szHeaders NULL goto cleanup dwSize WinHttpQueryHeaders rcContext hRequest WINHTTP_QUERY_RAW_HEADERS_CRLF WINHTTP_HE
408. ndow hWnd return FALSE Get a HDC for the default printer hdcPrinter GetPrinterDC if hdcPrinter return FALSE Get the HDC for the entire window hdcWindow GetWindowDC hWnd Get the rectangle bounding the window GetWindowRect hWnd amp rc Adjust coordinates to client area OffsetRect rc rce left rce top Get the resolution of the printer device iWidth GetDeviceCaps hdcPrinter HORZRES iHeight GetDeviceCaps hdcPrinter VERTRES Create the intermediate drawing surface at window resolution hbm Create24BPPDIBSection hdcWindow rec right rc bottom if thbm DeleteDC hdcPrinter ReleaseDC hWnd hdcWindow return FALSE Prepare the surface for drawing hdcMemory CreateCompatibleDC hdcWindow SelectObject hdcMemory hbm Get the current system palette hPal GetSystemPalette If a palette was returned 339 if hPal Apply the palette to the source DC SelectPalette hdcWindow hPal FALSE RealizePalette hdcWindow Apply the palette to the destination DC SelectPalette hdcMemory hPal FALSE RealizePalette hdcMemory Copy the window contents to the memory surface BitBlt hdcMemory 0 0 rec right rc bottom hdcWindow 0 0 SRCCOPY Prepare the DOCINFO ZeroMemory amp di sizeof di di cbSize sizeof di di lpszDocName Window Con
409. ndowTextLength hEdit SetFocus hEdit SendMessage hEdit EM_SETSEL WPARAM ndx LPARAM ndx Once the caret is placed at end in the edit control you can use the EM_REPLACESEL to append text to the edit control An application sends an EM_REPLACESEL message to replace the current selection in an edit control with the text specified by the lpszReplace lParam parameter Because there is no current selection the replacement text is inserted at the current caret location This example sets the selection to the end of the edit control and inserts the text in the buffer SendMessage hEdit EM_SETSEL WPARAM ndx LPARAM ndx SendMessage hEdit EM_REPLACESEL 0 LPARAM LPSTR szBuffer Another way to insert text into an edit control is to use the Windows clipboard If the applica tion has the clipboard open or finds it convenient to open the clipboard and copies the text into the clipboard then it can send the WM_PASTE message to the edit control to append text Of course any data that was in the clipboard will be lost Before sending the WM_PASTE message the caret must be placed at the end of the edit con trol text using the EM_SETSEL message Below is pseudo code that shows how to imple ment this method OpenClipBoard EmptyClipBoard SetClipBoardData SendMessage hEdit EM_SETSEL WPARAM ndx LPARAM ndx SendMessage hEdit WM_PAST
410. ndows application create one initialize stdout and use it as you would normally use it from a native console application include lt windows h gt include lt stdio h gt include lt fcntl h gt int main void tnt Were FILE hf AllocConsole hCrt _open_osfhandle long GetStdHandle STD_OUTPUT_HANDLE _O_TEXT hf fdopen hCrt w stdout hf setvbuf stdout NULL _IONBF 0 printf Hello world n return 0 2 21 17 Enabling or disabling a button or control in a dialog box You should first get the window handle of the control using hwndControl GetDigItem hwndDlg IDBUTTON Using that window handle call EnableWindow 2 21 18 Making a window class available for all applications in the system Under 32 bit Windows and Windows NT a style of CS_GLOBALCLASS indicates that the class is available to every DLL in the process not every application and DLL in the system as it does in Windows 3 1 To have a class registered for every process in the system under Windows NT e Register the class ina DLL e Use a style of CS_GLOBALCLASS e List the DLL in the following registry key HKEY_LOCAL MACHINE SOFTWARE Microsoft Windows NT CurrentVersion Windows AppInit_DLLs This will force the DLL to be loaded into every process in the system thereby registering the class in each and every process NOTE This technique does not work under Windows 95 344 C Tutori
411. ndows uses the features of windows We will start with the simplest application that uses windows a dialog box with a single edit field that will input a character string and show it in a message box at exit The easiest way to do this is to ask wedit to do it for you You choose new project in the proj ect menu give a name and a sources directory and when the software asks you if it should generate the application skeleton for you you answer yes You choose a dialog box application when the main dialog box of the wizard appears since that is the simplest application that the wizard generates and will fit our purposes quite well But let s go step by step First we create a project The first thing you see is a dialog box not very different from the one we are going to build that asks for a name for the new project You enter a name like this Enter the new project name Project name dialog Eral You press OK and then we get a more complicated one that asks quite a lot of questions 98 note 82 228 C Tutorial You enter some directory in the second entry field make sure the windows executable at the Definition of a new project d Icc examples dialog d Icc examples dialog iec bottom is selected and press ok Then we get You press the yes button This way we get into the wizard Information Introduction to windows programming 229 The first pa
412. nds us in smaller pieces disassembling the message information into its constituent parts This macro ends calling the MainWndProc_OnCommand function that is a bit higher in the text There you will find a switch with the comment TODO Insert new commands here Well do exactly that and add as a new case in the switch your new identifier IDMENU_ASK_PARAMETERS There you can do whatever you want to do when that menu item is clicked 2 8 2 Adding a dialog box Draw the dialog box with controls and all that in the resource editor and then open it as a result of a menu option for instance You would use DialogBox that handy primitive explained in detail in the docs to fire up your dialog 3 You have to write the procedure to handle the dialog box s messages first You can start the dialog box in a non modal mode with the CreateDialog API To make this a bit more explicit let s imagine you have defined your dialog under the name of IDD_ASK_PARAMS in the resource editor 124 You add a menu item corresponding to the dia log in the menu editor one that will return IDM_PARAMETERS say You add then in the func tion MainWndProc_OnCommand code like this case IDM_PARAMETERS r DialogBox hInst 122 Go to help then click in Win API get to the index and write the name of that function 123 Again this is the defined identifier of the dialog not the dialog s ti
413. ne that the malicious user prepared for us This kinds of exploits can be avoided if we use other functions of the standard library else p 0 strncpy fullname stream gt Name sizeof fullname strncat fullname sizeof fullname p strncat fullname name sizeof fullname Those functions test for overflow conditions and are safer in case of unforeseen input patterns There is a problem with strncpy though It does NOT terminate the resulting string with a zero If we get a Name field with exactly sizeof fullname chars the string will be missing the trailing zero since strncpy doesn t add it One way to cover this possibility is to do else p 0 fullname sizeof fullname 1 0 strncpy fullname stream gt Name sizeof fullname 1 strncat fullname sizeof fullname 1 p strncat fullname name sizeof fullname 1 We finish fullname with a zero and we copy only up to sizeof fullname 1 chars leaving our terminating zero intact But you should have noted that there is something wrong here We do initialize the terminating zero within an else statement What happens if the execution of the function takes the other path We see the following FILE Fopen STREAM stream char name char mode FILE result Buffer overflows 137 char fullname 1024 p p strrchr stream gt Name if p NULL fullname 0 0 els
414. ne using the double precision values found at those positions int compare const void ppl const void pp2 const int pl ppl p2 pp2 double vall values p1 double val2 values p2 if vall gt val2 return 1 else if vall lt val2 return 1 else return 0 int main void int i r We fill the array of double precision values with a random number for demonstration purposes At the same time we initialize our indexes array with a consecutive sequence of 0 lt i lt N for i 0 i lt N i r rand values i double r indexes i i Now we call our qsort function qsort indexes N sizeof int compare We print now the values array the indexes array and the sorted vector for i 0 i lt N itt printf Value 6 0 index 3d 6 0f n values i indexes i values indexes i return 0 Another possibility is to make a structure containing a value and an index and sort a table of those structures instead of sorting the values array directly but this solution is less efficient in space terms Pointers and references 107 1 18 3 Summary of Arrays and sorting e Arrays are declared by indicating their size in square brackets after the identifier declaration lt type gt identifier SIZE e Arrays are equivalent to pointers to their first element e Arrays decay i e are transformed into pointers when passed to other functions e
415. ned at 8 byte boundaries float double The C language defines the minimum sizes that all types must have in all implementations Specifically Same as in the 32 bit version Minimum size of standard types Type Minimum size char 8 bits short 16 bits int 16 bits long 32 bits long long 64 bits The double type uses the SSE regis ters in the Intel architecture version 1 7 Declarations and definitions 5 It is very important to understand exactly the difference between a declaration and a definition in C A declaration introduces an identifier to the compiler It says in essence this identifier is a xxx and its definition will come later An example of a declaration is extern double sqrt double 25 The C standard paragraph 5 2 4 2 2 Declarations and definitions 21 With this declaration we introduce to the compiler the identifier sqrt telling it that it is a func tion that takes a double precision argument and returns a double precision result Nothing more No storage is allocated for this declaration besides the storage allocated within the compiler internal tables 7 A definition tells the compiler to allocate storage for the identifier For instance when we defined the function main above storage for the code generated by the compiler was created and an entry in the program s symbol table was done In the same way when we wrote int count ab
416. ned ones The C language allows you to go one step further in this direction by allowing you to specify a new type definition or typedef for short This syntax for doing this is like this typedef lt already defined type gt lt new name gt For instance you can specify a new type of integer called my integer with typedef int my_integer Then you can use this new type in any position where the int keyword would be expected For instance you can declare my_integer i instead of Structures and unions 115 int i This can be used with structures too For instance if you want to avoid typing at each time you use a coordinate struct coordinate a you can define typedef struct coordinate COORDINATE and now you can just write COORDINATE a what is shorter and much clearer This new name can be used with the sizeof operator too and we can write GC_malloc sizeof COORDINATE instead of the old notation But please keep in mind the following once you have defined a typedef never use the struct keyword in front of the typedef keyword if not the compiler will get really confused 1 20 4 Unions Unions are similar to structures in that they contain fields Contrary to structures unions will store all their fields in the same place They have the size of the biggest field in them Here is an example union intfloat int i double d This union has two fields an integer and a double prec
417. ned the number 78 Note that the data that will initialize the structure is enclosed in curly braces Structures can be recursive i e they can contain pointers to themselves This comes handy to define structures like lists for instance struct list struct list Next int Data Here we have defined a structure that in its first field contains a pointer to the same structure and in its second field contains an integer Please note that we are defining a pointer to an iden tical structure not the structure itself what is impossible A structure can t contain itself Double linked list can be defined as follows struct dl list struct dl list Next struct dl_list Previous int Data This list features two pointers one forward to the following element in the list and one back ward to the previous element of the list A special declaration that can only be used in structures is the bit field declaration You can specify in a structure a field with a certain number of bits That number is given as follows struct flags unsigned HasBeenProcessed 1 unsigned HasBeenPrinted 1 unsigned Pages 5 Structures and unions 111 This structure has three fields The first is a bit field of length 1 i e a Boolean value the sec ond is also a bit field of type Boolean and the third is an integer of 5 bits In that integer you can only store integers from zero to 31 i e from zero to 2 to the 5th power minus one In
418. nel of the wizard is quite impressing with many buttons etc Ignore all but the type of application panel There select a dialog based application like this Application characteristics CE E gi hiSlecSlib wizard d icc examples dialog iage ooo You see the Dialog based check button at the upper left is checked Then press the OK but ton Then we get to different dialogs to configure the compiler You leave everything with the default values by pressing Next at each step At the end we obtain our desired program For windows standards this is a very small program 86 lines only including the commentaries We will study this program in an in depth manner But note how short this program actually is Many people say that windows programs are impossible huge programs full of fat This is just not true But first we press F9 to compile it Almost immediately we will obtain dialog exe built successfully 0 0 sec 230 C Tutorial Dialog exe built successfully Well this is good news Let s try it You execute the program you just built using Ctrl F5 When we do this we see our generated program in action dialog Just a dialog box with the famous OK Cancel buttons and nothing more But this is a start We close the dialog either by pressing the x button at the top right corner or just by using OK or Cancel they both do the same thing now since the dialog box is empty We com
419. ninet lib import library 3 5 Querying the network parameters The program ipconfig shows the parameters of the TCPIP configuration We will make here a similar program to give you an idea how you can get those parameters under program control We will use the APIs defined in the IP helper API The header file is iphlp h and the library to include is iphlp lib The interface for our program is very simple There is no parameters and the return value is zero if everything went OK an error code otherwise include lt stdio h gt include lt stdlib h gt include lt string h gt include lt windows h gt include lt winsock2 h gt include lt iphlpapi h gt 141 The FTP protocol has two modes of transmission binary where no modifications are done to the transmitted data and text where the sequence r n will be translated as a single n The text mode will destroy an executable file or zip file that can contain embedded r n sequences Querying the network parameters 395 int main void FIXED_INFO pFixedInfo IP_ADDR_STRING pIPAddr ULONG ulOutBufLen DWORD dwRetVal int rey We use the GetNetworkParams API to query the host name the domain name and other related information We make two calls in the first one we give an insufficient buffer This call fails obviously returning in the ulOutBufLen the necessary buffer length Using this information we allocate the necessary memory and then call GetNetw
420. not the case under windows Furthermore under UNIX all sockets descriptors are small positive numbers This is not the case under windows You will see under UNIX code that looks like this s socket if s 1 or s lt 0 This will not work under windows or produce a series of compiler warnings about signed unsigned comparisons The preferred style is as shown above comparing explictely with the NVALID_SOCKET constant 3 7 2 Server side 3 7 2 1 Binding a socket For a server to accept client connections it must be bound to a network address within the sys tem This code demonstrates how to bind a socket to an IP address and port Client applica tions use the IP address and port to connect to the host network First we create a sockkaddr object that contains the type of network we use AF_INET the server IP number we use the local loop address 127 0 0 1 and the port in that IP number we want to connect to We can use any port number between 1024 and 65535 sockaddr_in service service sin_family AF_INET service sin_addr s_addr inet_addr 127 0 0 1 service sin_port htons 49025 Second we bind the socket to this network address int rc bind m_socket SOCKADDR amp service sizeof service if rc SOCKET_ERROR printf bind failed n 3 7 2 2 Listening on a socket After the socket is bound to an IP address and port on the system the
421. ns Predefined data formats exist for images CF_BITMAP CF_METAFILEPICT CF_TIFF sound CF_WAVE CF_RIFF text CF_TEXT pen data CF_PENDATA a list of files CF_HDROP and sev eral others When you pass a block of data to the clipboard that memory should be allocated since win dows expects that it can free it when it is no longer used Since it is the clipboard that should free the allocated me mory you can t use the standard allocation functions you should use the GlobalAlloc API to get memory to be used by the clipboard To transfer a character string to the clipboard then we could use the following function int CopyTocl int len ipboard char str HWND hwnd strlen str 1 HANDLE h h GlobalAlloc GHND GMEM DDESHARE len if h HANDLE 0 Etc 315 return 0 txt GlobalLock h strcpy txt str if OpenClipboard hwnd EmptyClipboard SetClipboardData CF_TEXT h CloseClipboard return TRUE return FALSE We allocate space for our character string then obtain a pointer from the given handle We can then copy the data into this memory block We obtain access to the clipboard by opening it giving it the handle of a window that will own the clipboard If the operation succeeds we clear the previous contents set our data and we are done 2 17 2 Serial communications You use the same primit
422. ns the time when this object is active It can be 1 Permanent the object is always there and lives from the start to the end of the program It can maybe even live after the program has finished They are declared at global scope The initial value is either explicitly given by the program such as in int p 78 or implicitly defined as zero as in int p 2 Transitory The object starts its life when the program enters the scope where it lives and disappears after the program leaves the scope Automatic variables are transitory objects The initial value is undefined and in most compilers it consists of whatever values were stored previously at that memory location 3 Allocated The object starts its life as the result of one of the allocation functions like malloc or GC_malloc and it ends its life when its storage is reclaimed either explicitly because the programs calls the free function or because the garbage collector determines that its storage is no longer used The initial value depends on the allocation function malloc returns uninitialized memory calloc and Gc_malloc zeroes the memory before returning it 1 7 6 Variable definition A variable is defined only when the compiler allocates space for it For instance at the global level space will be allocated by the compiler when it sees a line like this int a or int a 67 In the first case the compiler allocates sizeof int bytes in the non initialized variables sec
423. nt a number that is specific to the data For instance we can construct a number from character strings by just adding the characters in the string This number is truncated module the number of elements in the table and used to index the hash table We find at that slot the head of a list of strings or other data that maps to the same key modulus the size of the table To make things more specific let s say we want a hash table of 128 elements which will store list of strings that have the same key Suppose then we have the string abc We add the ASCII value of a b c and we obtain 97 98 99 294 Since we have only 128 positions in our table we divide by 128 giv ing 2 and a rest of 38 We use the rest and use the 3gth position in our table This position should contain a list of character strings that all map to the 38 position For instance the character string aE 97 69 166 mod 128 gives 38 Since we keep at each position a single linked list of strings we have to search that list to find if the string that is being added or looked for exists A sketch of an implementation of hash tables looks like this define HASHELEMENTS 128 typedef struct hashTable int hashfn char string LIST Table HASHELEMENTS HASH_TABLE We use a pointer to the hash function so that we can change the hash function easily We build a hash table with a function HASH TABLE newHashTable int
424. nt that the macro resembles exactly a function call and you have to include a block of statements within the body of the macro for instance to declare a temporary variable define s2 x y int temp x xty y x tempty temp t6 If you call it like this if x lt y s2 x y else x 0 This will be expanded to if x lt y int temp x x ty y x tempty tempt6 else x 0 This will provoke a syntax error To avoid this problem you can use the do while statement that consumes the semicolon define s2 x y do int temp x xty y x tempty temp 6 A closer look at the pre processor 169 while 0 Note the that continues this long line and the absence of a semicolon at the end of the macro An undef statement can undo the definition of a symbol For instance undef PI will erase from the pre processor tables the PI definition above After that statement the iden tifier PI will be ignored by the preprocessor and passed through to the compiler The second form of pre processor instructions that is important to know is the if expression program text else program text endif or the pair ifdef symbol else endif When the preprocessor encounters this kind of directives it evaluates the expression or looks up in its tables to see if the symbol is defined If it is the if part evaluates to true and the text until the else or the endif is copied to the ou
425. ntations of equivalent functions with some added safety features 1 Freeing NULL is allowed and is not an error the same behavior of the standard free function Memory management strategies 149 2 Double freeing is made impossible 3 Any overwrite immediately at the end of the block is checked for 4 Memory is initialized to zero 5 A count of allocated memory is kept in a global variable include lt stdlib h gt define MAGIC OxFFFF define SIGNATURE 12345678L This global variable contains the number of bytes allocated so far size_t AllocatedMemory Allocation function void allocate size_t size char r int ip NULL size 3 sizeof int r malloc size if r NULL return r AllocatedMemory size ip int r At the start of the block we write the signature xip SIGNATURE Then we write the size of the block in bytes ipt int size We zero the data space memset ip 0 size 3 sizeof int We write the magic number at the end of the block just behind the data ip int amp r size sizeof int ip MAGIC Return a pointer to the start of the data area return r 2 sizeof int Freeing the allocated block void release void pp int ip NULL int s register char p pp if p NULL Freeing NULL is allowed return The start of the block is two integers before the data p 2 sizeof int ip int p if
426. nted with a width directive too Width direc tives are quite handy when building tables to get the items of the table aligned with each other in the output The first thing we do is to build a test file to see if our program is working correctly We build a test file containing ABCDEFGHIJK And we call lcc frequencies c leclnk frequencies obj frequencies fexample and we obtain D lcc examples gt frequencies fexample 13 chars in file 10 1 13 1 65 66 67 68 69 70 71 72 73 74 75 PRPRPRPRPRPRPHPHEH AUHPtQAAHAHON WP i Fe ee ee ee ed hr We see that the characters r 13 and new line 10 disturb our output We aren t interested in those frequencies anyway so we could just eliminate them when we update our Frequencies table We add the test if c gt Frequencies c i e we ignore all characters with value less than space r n or whatever Note that we ignore tabulations too since their value is 8 The output is now more readable H lcc examples gt frequencies fexample 100 C programming with Icc win32 13 chars in file 65 1 66 67 68 69 70 71 72 73 74 75 RUHMAWAAOA WwW Pp PRPPRPPRPRPHPHH We test now our program with itself We call frequencies frequencies c 758 chars in file I have organized the data in a table to easy the display
427. nterface structure we set some fields and there we go int main int argc char argv PingInterface p Ine es memset amp p 0 sizeof p We set the host name field p HostName argv 1l We modify the default time between packets p SleepTime 500 lf we time out more than 5 times we exit p MaxTimeouts 5 We set our callback p Callback PrintReport r ping amp p if 0 printf s is down n p HostName return 1 printf n printf n d packets from s s p TotalPackets p HostName p ip printf Received d Sent d n p TotalReceived p TotalSent if p TotalPackets 0 p TotalPackets 1 400 C Tutorial printf Max time d ms Min time d ms Avg time g ms n p MaxTime p MinTime double p TotalTime double p TotalPackets return 0 3 7 Client Server programming using sockets There are two distinct types of socket network applications Server and Client The server is normally the propietary of a ressource a data file an image or other information that it serves to its clients Clients request information from the server and display it to the user Servers and Clients have different behaviors therefore the process of creating them is differ ent Client Server Initialize WSA Initialize WSA Create a socket Create a socket Connect to the server Listen on the socket Accept a connection Send and re
428. o modify environment variables permanently 367 How do add a new directory to the PATH variable permanently 368 How do add a menu item to the explorer right click menu 370 How do translate between dialog units and pixels 371 initialize in WM_CREATE but the values of my variable change Why 371 How do translate between client coordinates to screen coordinates 372 When should use critical sections and when is a mutex better 372 Why is my call to CreateFile failing when use conin or conout 372 How can control the task bar under program control 373 How to erase a file into the recycle bin 373 Making a timed message box 378 How do I build a Property sheet control 379 How to tell Windows to run a program during startup 381 How do I disable the screen saver 381 How do I play a sound 381 How do simulate a key stroke to send it to another window 381 How can encrypt and decrypt a character string 382 Finding more examples and source code 384 Overview of Icc win s documentation 384 Bibliography 385 Books 385 URLs 386 Chapter 3 Network Programming 387 Introduction 387 What is a network 387 Protocols 388 The HTTP Protocol 388 GetHttpUrl 389 Implementation 390 The FTP protocol 393 Implementing the ftp GET 393 Querying the network parameters 394 Writing ping 398 How does it work 398 Client Server programming using sockets 400 Common steps for server and client 400 Server side 401 Clien
429. o handle the messages with the WM_NOTIFY interface you should add code to handle the message of interest in the window procedure Suppose for instance that you have a tree con trol and you want to be notified when the user has clicked on an an item with the right mouse button case WM_NOTIFY LPNMHDR nmhdr LPNMHDR lParam switch nmhdr gt code case NM_RCLICK TV_HITTESTINFO testInfo The structure testInfo will be filled with the coordinates of the item at this particular point memset amp testInfo 0 sizeof TV_HITTESTINFO Get the cursor coordintes GetCursorPos amp testInfo pt ptl testInfo pt Translate the coordinates into coordinates of the tree window MapWindowPoints HWND_DESKTOP hwndTree amp testInfo pt 1 125 See The windows user interface in the online documentation of lcc win 272 C Tutorial Now ask the tree view control if there is an item at this position hti TreeView_HitTest hwndTree amp testInfo If nothing is found stop if hti HTREEITEM 0 break There is something Show the context menu using the information returned by the control in the item handle hti hnewMenu CreateContextMenu hti If the creation of the menu did not work stop if hnewMenu HMENU 0O break menultem TrackPopupMenu hnewMenu TPM_RIGHTBUTTON TPM_TOPALIGN TPM_RETURNCMD ptl x ptl y 0 hwnd NULL DestroyMenu hnewMenu Here we would do
430. o resize a column in a table List view Used to display images and text Pager Used to make a scrollable region that contains other controls You scroll the controls into view with the pager Progress bar Used in lengthy operations to give a graphic idea of how much time is still needed to finish the operation Used to pack several dialog boxes into the same place avoiding Properly sheets user confusion by displaying fewer items at the same time Allows editing text with different typefaces bold italic with Richedit different fonts in different colors The basic building block to build a text processor Status bars Used to display status information at the bottom of a window Tab controls The building block to make property sheets Toolbar controls A series of buttons to accelerate application tasks Tooltips Show explanations about an item currently under the mouse in a pop up window Trackbars Analogical volume controls for instance 322 C Tutorial Tree view Displays hierarchical trees 2 18 Advanced windows techniques Windows is not only drawing of course It has come a long way since windows 3 0 and is now a sophisticated operating system You can do things like memory mapped files for instance that formerly were possible only under UNIX Yes mmap exists now under windows and it is very useful 2 18 1 Memory mapped files Memory mapped files al
431. obscure and difficult to track bugs that Memory management strategies 147 need advanced programming skills to find And the possibilities of errors are numerous freeing twice a memory block passing a wrong pointer to free forgetting to free a block etc 2 The time used by memory allocation functions can grow to an important percentage of the total run time of the application The complexity of the application increases with all the code needed to keep track and free the memory blocks 3 This strategy suffers from the memory fragmentation problem After many malloc free cycles the memory space can be littered with many small blocks of memory and when a request for a big block of memory arrives the malloc system fails even if there is enough free memory to satisfy the request Since it is impossible for the malloc system to move memory blocks around no memory consolidation can be done 4 Another problem is aliasing i e when several pointers point to the same object It is the responsibility of the programmer to invalidate all pointers to an object that has been freed but this can be very difficult to do in practice If any pointer to a freed object remains in some data structure the next time it will be used the program can catastrophically fail or return invalid results depending on whether the block was reallocated or not 5 It can be slow Malloc free was a big bottleneck for performance using the Microsoft C runtime provided by th
432. ocess if EnumProcessModules hProcess amp hMod sizeof hMod amp cbNeeded GetModuleBaseName hProcess hMod szProcessName sizeof szProcessName CloseHandle hProcess return szProcessName Note that you should add the library PSAPI LIB to the linker command line You should do this in the linker tab in the configuration of wedit A more complex example a clone of spy exe 281 And now we are done Each time you click in an item window the program will display the associated information in the status bar E windowtree lolx File Help Desktop BaseBar tooltips_class32 BaseBar tooltips_class32 BaseBar H BaseBar tooltips_class32 Avance Sound Effect Control Panel AlcEaxCplClass e tooltips_class32 tooltips_class32 NetDDE Agent NDDEAgnt e tooltips_class32 windowtree windowtreeWndClass tooltips_class32 Project windowtree TreeViewClass smallTextPopup wedit windowtree d downloads windowtree windowtree c cIMDIFrame E MDIClient m WeditOutput H C tutorial doc Microsoft Word OpusApp Stop Current Jump OfficeTooltip fan Edit MsoCommandBarPopup be Edit Picture MsoCommandBar rel Anuicdinn x Handle 0x34013a Visible left 396 top 8 right 1127 bottom 928 height 920 width 731 Process wedit exe 7 Summary There are many things that could be improved in this small program For instance it could be useful
433. of the program but this is a matter of personal taste 116 C programming with Icc win32 char FileName int LastUse struct networkSource int socket char ServerName int LastUse struct windowSource WINDOW window int LastUse All of this data structures should represent a source of information We add the following defines define ISFILE 1 define ISNETWORK 2 define ISWINDOW 3 and now we can define a single information source structure struct Source int type union struct fileSource file struct networkSource network struct windowSource window info We have an integer at the start of our generic Source structure that tells us which of the fol lowing possible types is the correct one Then we have a union that describes all of our possi ble data sources We fill the union by first assigning to it the type of the information that follows an integer that must be one of the defined constants above Then we copy to the union the corresponding structure Note that we save a lot of wasted space since all three structures will be stored beginning at the same location Since a data source must be one of the structure types we have defined we save wasting memory in fields that would never get used Another usage of unions is to give a different interpretation of the same data For instance an MMX register in an x86 compatible processor can be viewed as two integers of 32 bits 4 inte
434. ogical AND operator xx amp amp expression Negative powers of two 0 5 0 25 0 125 etc could share this same property in a suitable fraction representation 0 5 would be 0 1 0 250 would be 0 01 0 125 would be 0 001 etc This snippet and several others are neatly explained in http www caam rice edu dougm twiddle 1 17 5 striwr Given a string containing upper case and lower case characters transform it in a string with only lower case characters Return a pointer to the start of the given string This is the library function st rlwr In general is not a good idea to replace library functions even if they are not part of the standard library as defined in the C standard like this one We make the transformation in place i e we transform all the characters of the given string This supposes that the user of this program has copied the original string elsewhere if the orig inal is needed again include lt ctype h gt needed for using isupper and tolower include lt stdio h gt needed for the NULL definition char strTolower char str iterates through str unsigned char p unsigned char str if str NULL return NULL while p str tolower p ptt return str We include the standard header ctype h which contains the definition of several character classification functions or macros like isupper that determines if a given character is upper case a
435. ogram has performed an invalid operation and will terminate that windows shows up when a machine fault is detected In other cases you will be unlucky and the de referencing will yield a non sense result 45 Message ID lt dalc0101dj6 news4 newsguy com gt Newsgroups comp lang c Subject Re why use gt not with pointers Date 30 Jun 2005 18 00 53 GMT 72 C programming with Icc win32 For instance this program will crash int main void char p p 0 return 1 We have never assigned to p an object where it should point to We are using a dangling pointer When we follow this program we obtain fae wedit crash c A int main void char p return 1 OxfffaSaSa The debugger tells us that a machine exception has occurred with the code Oxc0000005 This means that the CPU has detected an invalid memory reference and has called the exception mechanism of windows that notified the debugger of the problem Note the value of the pointer in the output window Oxfffa5Sa5a Lcec win follows the philosophy that the sooner you see an error the better When it allocates the stack frame of the function it will write this value to all memory that has not been explic itly initialized by the program When you see this value in the debugger you can be highly confident that this is an uninitialized pointer or variable This will not be done if you turn on optimizations In that case the pointe
436. ogram start Identifier will be a pointer to objects of the given type id type You add an asterisk for each level of int pa indirection A pointer to a pointer needs two asterisks etc pa will be a pointer to int type id int expr Identifier will be an array of int expr elements of the given type The expression must evaluate to a compile time constant or to a constant expression that will be evaluated at run time In the later case this is a variable length array int ptrArray 56 Array of 56 int pointers typedef old new Define a new type name for the old type see Typedef on page 58 typedef unsigned int uint register id Try to store the identifier in a machine register The type of identifier will be equivalent to signed integer if not explicitly specified see Register on page 58 register int f extern type id The definition of the identifier is in another module No space is reserved extern int frequency static type id Make the definition of identifier not accessible from other modules static int f struct id struct coord Define a compound type composed of the listof int x declarations E fields enclosed within curly braces int y hi Within a structure field declaration declare id unsigned n 4 type id n as a sequence of n bits of type type See Bit n is an unsigned fields on page 62 int of
437. ogramming with Icc win32 The line five of file one was read and since file two is already finished we repeat it Is this a bug or a feature We received vague specifications Nothing was said about what the program should do with files of different sizes This can be declared a feature but of course is better to be aware of it We see that to test hypothesis about the behavior of a program there is nothing better than test data i e data that is designed to exercise one part of the program logic In many real cases the logic is surely not so easy to follow as in this example Building test data can be done automatically To build file one and two this small program will do include lt stdio h gt int main void FILE f fopen filel w for int i 0 i lt 8 i fprintf f File 1 Line d n i fclose f f fopen file2 w for int i 0 i lt 5 i fprintf f File 2 Line d n i fclose f return 0 This a good example of throw away software software you write to be executed once No error checking small and simple so that there is less chance for mistakes And now the answer to the other bug above Using arrays and sorting 97 One of the first things to notice is that the program tests with strcmp to see if two files are the same This means that when the user passes the command line paste Filel filEl our program will believe that they are different when in fact they are n
438. oint of view It is not object oriented but you can do object ori ented programming in C if you wish Objective C generates C as does Eiffel and several other object oriented languages C precisely because of this lack of a programming model is adapted to express all of them Even C started as a pre processor for the C compiler C is not a functional language but you can do functional programming with it if you feel like See the Illinois FP language implementations in C and many other functional programming languages that are coded in C Most LISP interpreters and Scheme interpreters compilers are written in C You can do list processing in C surely not so easily like in lisp but you can do it It has all essential features of a general purpose programming language like recursion procedures as first class data types and many others that this tutorial will show you Many people feel that C lacks the simplicity of Java or the sophistication of C with its tem plates and other goodies True C is a simple language without any frills But it is precisely this lack of features that makes C adapted as a first time introduction into a complex high level language that allows you fine control over what your program is doing without any hidden features The compiler will not do anything else than what you told it to do The language 1 For an overview of the Icc win documentation see How to find more information 2 Dennis Ritchie wr
439. okes a trap immediately under Icc win and under most other compilers too The address zero is specifically not mapped to real addresses to provoke an immediate crash of the program In other environments the address zero may exist and a NULL pointer dereference will not provoke any trap but just reading or writing to the address zero 1 15 3 Pointers and arrays Contrary to popular folklore pointers and arrays are NOT the same thing In some circum stances the notation is equivalent This leads to never ending confusion since the language lacks a correct array type Consider this declarations int iArray 3 int pArray iArray This can lead people to think that pointers and arrays are equivalent but this is just a compiler trick the operation being done is int pArray amp iArray 0 Another syntax that leads to confusion is char msg Please enter a number This leads people to think that we can assign an entire array to a pointer what is not really the case here The assignment being done concerns the pointer that gets the address of the first ele ment of the character array 49 This wasn t the case in MSDOS for instance NULL pointers were made to point to a special location in memory where the compiler left a special value that was checked when the program exited If the value at the end of the program wasn t what it should be that meant that somewhere in the program a NULL pointer was used
440. omething explicit with a message or implicit like the solution we implemented above appears very often in windows programming and it is very difficult to give a general solution to it It depends a lot of course upon the application and its general style But personally J prefer explicit error messages rather than implicit ones When you receive an error message you know exactly what is wrong and you can take easily steps to correct it When you see a menu item disabled it is surely NOT evident what the hell is happening and why the software is disabling those options But there are other user interface considerations in our dialog box to take into account too One of them is more or less evident when you see how small the letters in the edit field are Dialog boxes use a default font that shows very thin and small characters It would be much better if we would change that font to a bigger one In the initialization procedure we set the font of the edit field to a predefined font Windows comes with several predefined items ready for you to use without much work One of them is the system font that comes in two flavors monospaced and proportional We use the mono spaced one Our initialization procedure then looks now like this static int InitializeApp HWND hDlg WPARAM wParam LPARAM lParam HFONT font font GetStockObject ANSI_FIXED_FONT SendDlgItemMessage hDlg IDENTRYFIELD WM_SETFONT WPARAM font 0 E
441. ompiler to write that number in there The fourth argument is our comparison function We just write it like that No casts are needed since we were careful to define our comparison function exactly as qsort expects To output the already sorted array we use again a for loop Note that the index of the loop is declared at the initialization of the for construct This is one of the new specifications of the C99 language standard that Icc win follows You can declare variables at any statement and within for constructs too Note that the scope of this integer will be only the scope of the enclosing for block It can t be used outside this scope Note that we have written the for construct without curly braces This is allowed and means that the for construct applies only to the next statement nothing more The printf n is NOT part of the for construct Ok now let s compile this example and make a few tests to see if we got that right c lcc examples gt sortargs aaa bbb hhh sss ccc nnn aaa bbb ccc hhh nnn sss OK it seems to work Now we have acquired some experience with qsort we can apply our knowledge to our frequencies example We use cut and paste in the editor to define a new compare function that will accept integers instead of char We build our new comparison function like this int compare const void argl const void arg2 return int argl int
442. on WinHttpOpen L lcc WinHTTP 1 0 WINHTTP_ACCESS_TYPE_DEFAULT_PROXY WINHTTP_NO_PROXY_NAME WINHTTP_NO_PROXY_BYPASS 0 Check to see if the session handle was successfully created if hSession NULL fRet GetLastError if fRet 0 fRet 1 return fRet The first argument to WinHttpOpen is the name of the application that issues the request for data or user agent The user agent is the client application that requests a document from an HTTP server so that the server can determine the capabilities of the client software In this case we send just a default name WinHttp uses a proxy if needed We rely that a configuration utility has already set up the proxy settings for us and request that WinHttp uses the default configuration If we can t open the session we just return the error code If all goes well we initialize our local variables We zero the rcContext structure where we store the relevant information for our session and we translate the name of the URL into UNI CODE The winhttp primitives are all in UNICODE and there is no ANSI equivalent Initialize local stuff ZeroMemory amp urlComp sizeof urlComp urlComp dwStructSize sizeof urlComp memset amp rcContext 0 sizeof rcContext mbstowcs SzWURL url 1 strlen url L Use allocated buffer to store the Host Name urlComp lpszHostName szHost urlComp dwHostNameLength
443. on however can return several return values if it modifies its environment 10 This example is a classic and appears already in the tutorial of the C language published by B W Kernighan in 1974 four years before the book The C programming language was published Their example would still compile today albeit with some warnings main printf Hello world n 11 This is one of the two possible definitions of the main function Later we will see the other one 12 Character strings can contain sequences of characters that denote graphical characters like new line n tab t backspace b or others In this example the character string is finished by the new line character n 4 C programming with Icc win32 6 The closing brace finishes the function scope Programs in C are defined in text files that normally have the c file extension You can create those text files with any editor that you want but Icc win proposes a specialized editor for this task called Wedit This program allows you to enter the program text easily since it is adapted to the task of displaying C source text To make this program then we start Wedit and enter the text of that program above 1 3 1 Program input If you know how an integrated development environment IDE works you can skip this sec tion When you click in the icon of Icc win you start a program designed to make it easy for you to type your program an
444. on to the dst location until it finds a zero byte in the src string No checks are ever done and it is assumed that the dst string contains sufficient space to hold the src string If not the whole program will be destroyed One of the most common errors in C program ming is forgetting these facts strcat appends a character string to another strcat src app will add all the char acters of app at the end of the src string For instance if we have the string pointer that has the characters lccwin32 as above and we call the library function strcat str compiler we will obtain the following sequence l c jce w i n 3 2 c jo Im p fi l e r 108 99 99 119 105 110 51 50 32 99 111 109 112 105 108 101 114 O The common operations for strings are defined in the header file lt string h gt Function Purpose Function Purpose Get a system error message strcat Appends strings strerror strerror or prints a user supplied error message _strerror 132 C programming with Icc win32 Find the first occurrence of a strchr character ina string strlen Find the length of a string Find the last occurrence of a strrchr strncat Append characters of a string character in a string Copy strings up to a maximum strcmp Compares two strings strncpy PY 8s up length Compare strin
445. on type as a function returning T A function type is characterized by the return type of the function and the types and numbers of its parame ters 16 C programming with Icc win32 1 6 2 Types classification This type classification is based on the classification published by Plauger and Brody slightly modified Types 1 Function types 1 1 Fully qualified function types Functions whose full prototype is visible 1 2 Assumed function types Functions whose prototype is partly or not visible 1 2 1 Functions whose return value is visible but not their arguments 1 2 2 Functions where the return value and their arguments are unknown 2 Incomplete types Types not completely specified 2 1 void 2 2 Incomplete struct types 2 3 Incomplete union types 2 4 Incomplete array types 3 Object types 3 1 Scalar types 3 1 1 Arithmetic types 3 1 1 1 Integer types 3 1 1 1 1 Standard integer types 3 1 1 1 1 1 boolean type 3 1 1 1 1 2 char signed unsigned 3 1 1 1 1 3 short signed unsigned 3 1 1 1 1 4 int signed unsigned 3 1 1 1 1 5 long signed unsigned 3 1 1 1 1 6 long long signed unsigned 3 1 1 1 2 Bitfields signed unsigned 3 1 1 1 3 Enumeration types 3 1 1 2 Floating types 3 1 1 2 1 Real types 3 1 1 2 1 1 float 3 1 1 2 1 2 double 3 1 1 2 1 3 long double 3 1 1 2 4 Complex types 3 1 1 2 4 1 float Complex 3 1 1 2 4 2 double Complex 3 1 1 2 4 2 long double Complex 3 1 2 Pointer types 22 http www ccs ucsd edu c types
446. onsole input or output handle by calling the CreateFile function with the special CONINS or CONOUTS filenames this call will return INVALID_HANDLE_VALUE if you do not use the proper sharing attributes for the fdwSha reMode parameter in your CreateFile call Be sure to use FILE_LSHARE_READ when open ing CONIN and FILE_LSHARE_WRITE when opening CONOUTS FAQ 373 2 22 25 How can I control the task bar under program control You can control the state of the task bar or query the characteristics using the SHAppBarMes sage API This is a complex API that allows you to change where the tasklbar is localted whether it is automatically hidden etc For instance this small program will show you if the task bar auto hide feature is on or off include lt shellapi h gt include lt stdio h gt int IsTaskbarAutoHideOn void APPBARDATA d d cbSize sizeof APPBARDATA return SHAppBarMessage ABM_GETSTATE amp ABData amp ABS _AUTOHIDE int main void printf Taskbar autohide if IsTaskbarAutoHideOn printf ON else printf OFF printf n 2 22 26 How to erase a file into the recycle bin When you erase a file within a program the deleted file doesn t appear in the recycle bin This can be annoying if you want to undo this operation of course The solution is to use the API SHFileOperation with the flag FOF_ALLOWUNDO Here is a small program that does all this f
447. ontent Close the message if hMsg CryptMsgClose hMsqg src capacity cbEncodedBlobt1 src count cbEncodedBlob src content pbEncodedBlob return 1 2 23 Finding more examples and source code John Finlay has created a web site for source code for lcc win Here is what John writes about his work When I initially started using LCC Win searching the Internet revealed no good sources of material that one could download as examples so creating a web site dedicated to this end seemed a good idea If I needed help obviously others would too The web site http www btinternet com john findlay1 contains many examples that lcc win users can easily compile and learn from I have tried to place each example in an appropriate section to help in locating as the number of examples would be bewildering if there were no discrete departments These departments sections however are not absolute as examples do not always readily fit into any specific category The largest section is Windows Programming where you will find examples ranging from a simple Generic application to far more sophisticated software There are many other sections that may be of interest OpenGL DirectX Windows Common Controls Custom Controls MultiMedia Telephony Games etc There is also the Assembler section with texts and examples explaining and showing how to code in assembler using Icc win specifically as the asm syntax used is
448. or you Compile with DTEST to have a standalone program that will accept command line arguments or without it to have just the Recycle function that 140 will erase a file to the recycle bin include lt windows h gt include lt stdio h gt include lt conio h gt include lt direct h gt include lt shellapi h gt MMT Send a file to the recycle bin Args full pathname of file bDelete if TRUE really delete file no recycle bin int Recycle LPCTSTR pszPath BOOL bDelete Copy pathname to double NULL terminated string 140 This program is based on a similar program published in MSDN magazine 2001 In the comments for that program I found the following If this code works it was written by Paul DiLascia If not I don t know who wrote it 374 C Tutorial char buf _MAX PATH 1 SHFILEOPSTRUCT sh strcpy buf pszPath buf strlen buf 1 0 allow one more character copy caller s path name need two NULLs at end SHFILEOPSTRUCT params for delete operation don t report progress don t report errors don t confirm delete REQUIRED delete operation REQUIRED which file s MUST be NULL if delete requested don t use Recycle Bin otherwise Set memset amp sh 0 sizeof SHFILEOPSTRUCT sh fFlags FOF_SILENT sh fFlags FOF_NOERRORUI sh fFlags
449. orkParams again This is a common interface with many network APIs that need buffers of varying length pFixedInfo malloc sizeof FIXED_INFO ulOutBufLen sizeof FIXED_INFO re GetNetworkParams pFixedInfo amp ulOutBufLen if rc ERROR_BUFFER_OVERFLOW free pFixedInfo pFixedInfo malloc ulOutBufLen else return GetLastError failed for another reason Exit Now this call is for real dwRetVal GetNetworkParams pFixedInfo amp ulOutBufLen if dwRetVal NO_ERROR printf Call to GetNetworkParams failed nError code d n GetLastError return 1 Show the retrieved information printf tHost Name s n pFixedInfo gt HostName printf tDomain Name s n pFixedInfo gt DomainName printf tDNS Servers n printf t t s n pFixedInfo gt DnsServerList IpAddress String The server list is stored as a linked list Go through that list until we hit a NULL pIPAddr pFixedInfo gt DnsServerList Next while pIPAddr printf t t s n pIPAddr gt IpAddress String pIPAddr pIPAddr gt Next Show the other parameters printf tEnable Routing s n pFixedInfo gt EnableRouting Yes No printf tEnable Proxy s n pFixedInfo gt EnableProxy Yes No printf tEnable DNS s n pFixedInfo gt EnableDns Yes No IP_ADAPTER_INFO pAdapteriInfo pAdapter The sam
450. ormat e is used if the exponent falls below 4 or is greater than the precision that defaults to 6 oe How do you insert a sign in your output Well by using this conversion 3 The printf family 79 1 14 4 1 Ata glance The printf family Name Description printf format Writes its output into the standard output sprintf string format Writes its output into a string snprintf string size format Writes its output into the given string but never exceeding size chars fprintf file format Writes its output into a file 1 14 5 Scanning values The scanf family of functions fulfills the inverse task of the printf family They scan a charac ter array and transform sequences of characters into values like integers strings or floating point values The general format of these functions are scanf format p1 p2 p3 Reads characters from stdin fscanf file format pl p2 p3 sscanf string format p1 p2 p3 where format is a character string like we have seen in printf and p1 p2 p3 are pointers to the locations where scanf will leave the result of the conversion For instance scanf d amp integer and the input line 123 will store the integer 123 at the location of the integer variable Some things to remember when using scanf 1 You have to provide always a format string to direct scanf 2 For each format directive you must
451. orting 101 The function qsort doesn t return an explicit result It is a void function Its argument list is the following Argument 1 isa void Void What is that Well in C you have void that means none and void that means this is a pointer that can point to anything i e a pointer to an untyped value We still haven t really introduced pointers but for the time being just be happy with this explanation qsort needs the start of the array that will sort This array can be composed of anything integers user defined structures double precision numbers whatever This whatever is precisely the void Argument 2 is a size_t This isn t a known type so it must be a type defined before in stdlib h By looking at the headers and following the embedded include directives we find stdlib h includes stddef h that defines a typedef like this gt typedef unsigned int size_t This means that we define here a new type called size_t that will be actually an unsigned integer Typedefs allow us to augment the basic type system with our own types Mmmm interesting We will keep this for later use In this example it means that the size_t n is the number of elements that will be in the array Argument 3 is also a size_t This argument contains the size of each element of the array i e the number of bytes that each element has This tells qsort the number of bytes to skip at each increment
452. ot Windows is not case sensitive for file names The right thing to do there is to compare the file names with stricmp that ignores the differences between uppercase and lowercase But an even greater problem is that we do not test for NULL when opening the files If any of the files given in the command line doesn t exist the program will crash Add the necessary tests before you use it Another problem is that we test if we have the right number of arguments i e at least two file names but if we have more arguments we simply ignore them What is the right behavior Obviously we could process and paste several files at once Write the necessary changes in the code above Note that if you want to do the program really general you should take into account the fact that a file could be repeated several times in the input i e paste filel file2 filel file3 Besides the separator char in our program is now hardwired to the tab character in the code of the program Making this an option would allow to replace the tab with a vertical bar for instance But the problem with such an option is that it supposes that the output will be padded with blanks for making the vertical bars align Explain why that option needs a complete rewrite of our program What is the hidden assumption above that makes such a change impossible Another feature that paste exe could have is that column headers are automatically under lined Explain why adding su
453. ote the pre processor that the Icc win system uses 2 C programming with Icc win32 remains transparent even if some features from Java like the garbage collection are incorpo rated into the implementation of C you are going to use As languages come and go C remains It was at the heart of the UNIX operating system devel opment in the seventies it was at the heart of the microcomputer revolution in the eighties and as C Delphi Java and many others came and faded C remained true to its own nature 1 2 Program organization A program in C is written in one or several text files called source modules Each of those modules is composed of functions i e smaller pieces of code that accomplish some task gt and data i e variables or tables that are initialized before the program starts There is a special function called main that is where the execution of the program begins In C the organization of code in files has semantic meaning The main source file given as an argument to the com piler defines a compilation unit Each compilation unit defines a name space i e a scope Within this name space each name is unique and defines only one object A unit can import common definitions using the include preprocessor directive or just by declaring some identifier as extern C supports the separate compilation model i e you can split the program in several indepen dent units that are compiled separately and t
454. ough to represent the number of atoms in the whole known universe Those numbers are defined as LDBL_MAX and LDBL_MIN in float h The number of significant digits is 18 defined as LDBL_DIG Note that even if the number of bits of the long double representation is 80 or ten bytes sizeof long dou ble is 12 and not 10 The reason for this is the alignment of this numbers in memory To avoid having numbers not aligned at addresses that are not multiple of four two bytes of pad ding are left empty 1 37 1 4 The qfloat format This format is specific to lcc win and was designed by Stephen Moshier the author of the Cephes mathematical library that lcc win uses internally Its description is as follows define _NQ_ 12 struct qfloatFormat unsigned int sign int exponent unsigned int mantissa _NQ This is defined in the qfloat h header file It provides 104 significant digits a fraction of 352 bits one word is left empty for technical reasons and a biased exponent of 32 bits The bias uses 0x8001 or 32769 1 37 1 5 Special numbers All the floating point representations include two numbers that represent an error or NAN and signed infinity positive and negative infinity The representation of NANs in the IEEE formats is as follows Numerical programming 195 type NAN Infinity and float 7 c00000 7 800000 ff800000 double 7 f80000 00000000 7 f00000 00000000 fff00000 0000000
455. ould be that the resource editor applies the changes letter by letter as the user types them in as some other editors do This has the advantage of being simpler to use but the disadvantage of being harder to program and debug As always an the appearance of the user interface is not only dictated by the user comfort but also by the programming effort necessary to implement it You will see this shortly when you are faced with similar decisions 288 C Tutorial We have at the left side the tree representing our menu Each submenu is a branch and the items in the branch the leaves are the items of the submenu We select the File submenu and press the insert key We obtain a display like this Menu editor File Edit Help A new item is inserted after the currently selected one The name is Popup and the first item is New item We can edit those texts in the window at the right We can change the symbolic name and set unset several options When we are finished we press Apply to write our changes to the resource 123 OK we change the default names to the traditional Edit and Search to obtain this display Menu editor File Edit Help We will name the new item IDM_SEARCH I am used to name all those constants starting with IDM_ from ID Menu to separate them in my mind from IDD_ ID Dialog We can now start drawing the Search dialog Just a simple one a text to sear
456. our applications of course How could we do that One way would be to call it as an independent program We could use the facilities for calling a program within the windows system and pass our prompt in the command line parameters This would work but the problem of getting the string from the user would be quite compli cated to solve Programs can only return an error code and in some situations this error code can only be from zero to 255 We can t pass pointers just like that from one program to another we can t just pass a pointer to a character string as the result of the program Why Because windows as other systems like linux Solaris and UNIX in general uses a protected virtual address schema The machine addresses that the program uses are virtual as if the pro gram was the only one running in the machine It is the operating system and the CPU that does the translation of those virtual addresses into real RAM locations in the machine you are using This means the addresses of each program aren t meaningful for another program We can pass special pointers shared memory within windows but that s too advanced stuff for an introductory text sorry But there are many other ways of solving this problem without costly interface development What do we want Let s get that clear first worrying about implementation details later int GetString char prompt char buffer int bufferlen This routine would return eithe
457. ove the compiler made space in the local variables area of the function to hold an integer And now the central point You can declare a variable many times in your program but there must be only one place where you define it Note that a definition is also a declaration because when you define some variable automatically the compiler knows what it is of course For instance if you write double balance even if the compiler has never seen the identifier balance before after this definition it knows it is a double precision number ah 1 7 1 Variable declaration A variable is declared with lt type gt lt identifier gt like int a double d long long h All those are definitions of variables If you just want to declare a variable without allocating any storage because that variable is defined elsewhere you add the keyword extern extern int a extern double d extern long long d Optionally you can define an identifier and assign it a value that is the result of some calcula tion double fn double f double d sqrt f more statements Note that initializing a value with a value unknown at compile time is only possible within a function scope Outside a function you can still write int a 7 or 26 Note that if the function so declared is never used absolutely no storage will be used A declaration doesn t use any space in the compiled program unless what is declared is effectively used
458. over other more basic protocols like the ethernet protocol in the case of coax or token ring or whataver is actually sending and receiving the data But let s get practical Let s start a small program that we can do without a lot of effort We will start then with a simple program to read files from the internet We will use the library of Microsoft provided with the operating system Winhttp 1ib The header file is winhttp h that you should include in all the programs that use this examples You should obviously include in the linker command line the library itself winhttp lib This library is just an import library for winhttp d11 that you should normally have in your windows direc tory Other header files are necessary too like stdlib h for getting the prototype of the malloc function etc 3 2 Protocols Protocols are standardized exchanges between two automata a client that asks some infor mation or resource from the server automaton that manages that information and sends it through the network A protocol has a standard interchange format the precise sequence of interactions between the two machines is fixed in all details to make automated communica tion between them possible The information exchanged can be anything an image sound an e mail hyper text you name it It can be even a pdf file where you read this lines 3 3 The HTTP Protocol The Hyper Text Transfer Protocol relies on transaction
459. ow you can resize the control by using the MoveWindow API The following code sample demonstrates how to do this This sample assumes that you have placed the combo box control in a dialog box LRESULT CALLBACK NewComboProc HWND hWnd UINT message WPARAM wParam LPARAM lParam prototype for the combo box subclass proc HANDLE hInst Current app instance BOOL bFirst A flag Dialog procedure for the dialog containing the combo box BOOL CALLBACK DialogProc HWND hDlg UINT message WPARAM wParam LPARAM 1Param FAQ 367 FARPROC lpfnNewComboProc switch message case WM_INITDIALOG bFirst TRUE Set flag here see below for usage Subclass the combo box lpfnOldComboProc FARPROC SetWindowLong GetDlgItem hDlg IDC_COMBO1 GWL_WNDPROC LONG NewComboProc break case WM_DESTROY FARPROC SetWindowLong GetDlgItem hDlg IDC_COMBO1 GWL_WNDPROC LONG lpfnOldComboProc break default break return FALSE End dialog proc Combobox subclass proc LRESULT CALLBACK NewComboProc HWND hWnd UINT message WPARAM wParam LPARAM lParam static HWND hwndList static RECT rectList if WM_CTLCOLORLISTBOX message 32 bits has new message Is this message for the list box control in the combo Do only the very first time get the list box handle and the list box rectangle Note the use of GetWindo
460. ow is then to do the following 1 Get the page size from the system 2 Set the page to guard page again An example is given below include lt intrinsics h gt For _GetStackPointer int main int argc char argv for __try StackOverflow 0 _ except EXCEPTION_EXECUTE_HANDLER LPBYTE lpPage static SYSTEM_INFO si static MEMORY_BASIC_INFORMATION mi static DWORD dwOldProtect Get page size of system GetSystemInfo amp si Find SP address lpPage _GetStackPointer Get allocation base of stack VirtualQuery lpPage amp mi sizeof mi Go to page beyond current page lpPage LPBYTE mi BaseAddress si dwPageSize Free portion of stack just abandoned if VirtualFree mi AllocationBase LPBYTE lpPage LPBYTE mi AllocationBase MEM DECOMMIT If we get here exit there is nothing that can be done 188 C programming with Icc win32 exit EXIT_FAILURE Reintroduce the guard page if VirtualProtect lpPage si dwPageSize PAGE_GUARD PAGE_READWRITE amp dwOldProtect exit EXIT_FAILURE printf Exception handler 1x n GetExceptionCode Sleep 2000 return 0 1 36 5 6 The _ retry construct You can correct the error condition that provoked the exception and then restart again using the __retry construct A simple example of this is the following include lt stdio h gt include lt seh h gt int main void char
461. p the initialization of the variable m A very bad idea since m can now contain any value 1 13 20 Return A return statement terminates the function that is currently executing and returns hence the name to the function that called the current function 1 13 20 1 Two types of return statements Since a function can return a value or not we have then two types of return statements return or return expression A return with no value is used in functions that have the return type void i e they do not return any value Functions that have a return type other than void must use the second form of the return statement It is a serious error to use an empty return statement within a function that expects a returned value The compiler will warn about this The type of the return will be enforced by the compiler that will generate any necessary con version For instance double fn void int a return a The compiler will generate a conversion from integer to double to convert a to double preci sion There is one exception to this rule If the function main does not return any value and con trol reaches the end of main the compiler will supply automatically a value of zero 1 13 20 2 Returning a structure When the return type of a function is a structure and that structure is big enough to make it impossible to return the value in the machine registers the compiler passes the address of a temporary
462. pdated when the code below changed and actually instead of help ing you to understand the code it contributes further to make it more obscure Do not comment what are you doing but why For instance record increment record by one This comment doesn t tell anything the C code doesn t tell us anyway record Pass to next record The boundary tests are done at Commenting the source code 37 the beginning of the loop above This comment brings useful information to the reader At the beginning of each procedure try to add a standard comment describing the purpose of the procedure inputs outputs error handling etc gt At the beginning of each module try to put a general comment describing what this module does the main functions etc Note that you yourself will be the first guy to debug the code you write Commentaries will help you understand again that hairy stuff you did several months ago when in a hurry The editor of Icc win provides a Standard comments feature There are two types of com ments supported comments that describe a function and comments that apply to a whole file This comments are maintained by the editor that displays a simple interface for editing them 1 10 1 Describing a function You place the mouse anywhere within the body of a function and you click the right mouse button A context menu appears that offers you to edit the description of the current function The interface that a
463. perator overloading 179 References 180 Generic functions 180 Default arguments 181 Structured exception handling 181 The signal function 188 Numerical programming 192 Floating point formats 193 What can we do with those numbers then 195 Using the floating point environment 203 The status flags 203 Reinitializing the floating point environment 204 Numerical stability 204 Complex numbers 206 The libraries of Icc win 208 The regular expressions libraries 208 Console formatting routines 208 Statistics library 208 Linear algebra library 208 Network utilities 209 Advanced math functions 209 Compression decompression functions 209 Structured Query Language SQL 209 Safer C Library 209 The regular expressions library A grep clone 209 Programming with security in mind 213 Always include a default in every switch statement 213 Pay attention to strlen and strcpy 213 Do not assume correct input 215 Watch out for trojans 215 Pitfalls of the C language 216 Defining a variable in a header file 216 Confusing and 216 Forgetting to close a comment 216 Easily changed block scope 216 Using the or more than once in an expression 217 Unexpected Operator Precedence 217 Extra Semi colon in Macros 218 Watch those semicolons 218 Assuming pointer size is equal to integer size 218 Careful with unsigned numbers 219 Changing constant strings 219 Indefinite order of evaluation 220 A local variable shadows a global one 220 Careful w
464. plemented with more sophisticated variations A common solution is to make the arena a linked list of blocks what needs a small processing overhead 2 Determining when the moment has come to release all memory is tricky unless the data processed by the program has a logical structure that adapts itself to this strategy Since there is no way of preserving data beyond the frontier where it is released data that is to be preserved must be copied into another location 1 30 4 The malloc free strategy This is the strategy that is most widely used in the C language The standard provides the func tions malloc a function that returns a pointer to an available memory block and free a func tion that returns the block to the memory pool or to the operating system The program allocates memory as needed keeping track of each memory block and freeing it when no lon ger needed The free function needs a pointer to the same exact location that was returned by malloc If the pointer was incremented or decremented and it is passed to the free function havoc ensues Advantages 1 Itis very flexible since the program can allocate as needed without being imposed any other limit besides the normal limit of available memory 2 It is economic since the program doesn t grab any more memory than it actually needs 3 Itis portable since it is based in functions required by the C language Drawbacks 1 It is very error prone Any error will provoke
465. point environment 205 The recurrence relation is given by I 1 1 5Ig I 1 2 5I I 1 3 5I etc We calculate this starting with 0 182322 We use the following program include lt stdio h gt include lt math h gt int main void float i 0 182322 for int z 1 z lt 9 z i 1 0 float z 5 0 i printf I 3d 9 6g n z i return 0 We use single precision Note the notation 1 0f meaning 1 in float precision Il 0 08839 I2 0 0580499 I3 0 0430839 I4 0 0345805 I5 0 0270974 I6 0 0311798 I7 0 0130418 I8 0 190209 The first few numbers look correct but I6 is bigger than I5 what after the recurrence relation should never happen Moreover I7 is negative and later numbers are complete nonsense Why Well because the roundoff error e in IO is multiplied by 5 in the first iteration then multiplied again by 5 in the next iteration so that after a few iterations the error becomes bigger than the result Writing this is double precision and replacing the precalculated constant with a computation of log 6 0 log 5 0 we get better results include lt stdio h gt include lt math h gt int main void double i log 6 0 log 5 0 for int z 1 z lt 29 z i 1 0 double z 5 0 i printf I 3d 9 6g n z i return 0 206 C programming with Icc win32 We get Tel 0 0883922 11 0 0140713 I21 0
466. pointer instead of the string pointer itself some people think once amp always amp sscanf s sscanf s amp str str wrong right Consider the following code include lt stdio h gt int main void int i char c scanf d amp 1i scanf Sc amp c printf Sd c n i c Assume you type 45 n in response to the first scanf The 45 is copied into variable n When the program encounters the next scanf the remaining n is quickly copied into the variable c The fix is to put explicitly a n like this scanf d n amp i Type Format char SC short shd int Sd or i long Sld long long Slld float sf or e double Sl1f or Sle long double SL or Sle string SS Pointers 81 1 15 Pointers Pointers are one of the great ideas in C but it is one that is difficult to grasp at the beginning All objects integers structures any data reside in RAM Conceptually memory is organized in a linear sequence of locations numbered from 0 upwards Pointers allow you to pass the location of the data instead of the data itself To make things explicit suppose you have some structure like this define MAXNAME 128 struct person char Name MAXNAME int Age bool Sex double Weight Instead of passing all the data to a function that works with this data you just pass the address where it starts What is this a
467. posed solution char dot_to_underscore const char s 97 Note that the versions of Icc win that relied on the system supplied calloc will fail they do not test for overflow I rewrote that function on Apr 18th 2006 and Icc win does not use the system provided cal loc any more Pitfalls of the C language 223 char t u if t u malloc strlen s 1 while ut t s s _ st return t Now I must confess that the second version baffled me at first sight Reading it closely we get while u s s _ s is the same as while u s st _ s since the while is just an empty loop Taking the out to make the code more readable we get while ut s _ s stt This is the same as while u if s u _ else u s stt utt The arguments advanced by Mr Twink were 1 Fewer lines make for more readable code You do not have to wade through a lot of code 2 His function is much more efficient than Mr Heathfield s because it doesn t make so many passes through the string It passes only twice one for the strlen call and another for making the changes Mr Heathfield s passes three times the strlen the strcpy and then the pass to make the changes Mr Heathfield answered that 1 This function was called once within the application Its efficiency is not at all crucial for the application whe
468. ppears by choosing this option looks like this There are several fields that you should fill Procedure description Name multiple Compiles a multiple regular expression Purpose Reads input from standard input Generates 4 regexp structure Several errors are displayed using the complain Ena function handling zi void multiple void d lcc examples regexp try c lines 115 Cancel 1 Purpose This should explain what this function does and how it does it 2 Inputs Here you should explain how the interface of this function is designed the arguments of the function and global variables used if any 37 The IDE of lcc win helps you by automatic the construction of those comments Just press edit description in the right mouse button menu 38 C programming with Icc win32 3 Outputs Here you should explain the return value of the function and any globals that are left modified 4 Error handling Here you should explain the error return and the behavior of the function in case of an error occurring within its body For the description provided in the screen shot above the editor produces the following out put Procedure multiple ID 1 Purpose Compiles a multiple regular expression Input Reads input from standard input Output Generates a regexp structure Errors Several errors are displayed using the complain funct
469. program will provoke a trap include lt stdio h gt int main void char p NULL 182 C programming with Icc win32 kn p 0 printf This will never be reached n return 0 There is no way you can catch this trap and try to recover or at least exit the program with an error message This means that there isn t any way for you to prevent your program from failing catastrophi cally at the smallest error It suffices to have a bad pointer somewhere and you are doomed If you use a third party library you have to trust it 100 meaning that the slightest problem in the library will provoke the end of your application The whole application is fragile and very difficult to trust A small error in ten thousands of lines is almost inevitable as you may know Of course there is already an exception handling mechanism When a machine trap occurs windows displays the well known This application message and shuts down the program Couldn t the system make something better Well it can do something better and it does Structured exception handling within Icc win is built using the general exception handling mechanism of windows It has been around since the beginning of the win API i e 1995 1 36 5 2 How do I use SEH Structured exception handling allows you to build a solution for the above problems You enclose the possibly buggy code within special markers like this include lt s
470. protected block of code _ except integer expression exception handler block If the integer expression evaluates to 1 the associated code block will be executed in case of an exception __leave Provokes an exit to the end of the current __ try block _retry Provokes a jump to the start of the try except block An overview of the whole language 47 1 11 6 Control flow if expression block If the given expression evaluates to something different than zero execute the else statements of the following block Else execute the statements of the block block following the else keyword The else statement is optional Note that a single statement can replace blocks while expression If the given expression evaluates to something different than zero execute the Statements statements in the block and return to evaluate the controlling expression again Else continue after the block See while on page 14 do statements while condition Execute the statements in the block and afterwards test if condition is true If that is the case execute the statements again See do on page 14 for init test incr Statements Execute unconditionally the expressions in the init statement Then evaluate the test expression and if evaluates to true execute the statements in the block following the for At the end of each iteration execute
471. put Frequencies return 0 We didn t have to change a lot thanks to the fact that the complexities of reading and handling a stream are now hidden in a function with well defined parameters We build a GetNext function that returns either a valid new stream or NULL if it fails It looks like this STREAM GetNext STREAM stream STREAM result struct _finddata_t fd long findnextResult _findnext stream gt handle amp fd if findnextResult lt 0 return NULL result malloc sizeof STREAM memcpy result gt FindData fd sizeof struct _finddata_t result gt handle stream gt handle result gt file fopen fd name rb return result In the same manner that we allocate RAM for our first STREAM we allocate now a new one and copy into it our finddata handle and we open the file We compile and we get a compiler warning D lcc examples gt lcc g2 freql c Warning freql c 44 missing prototype for memcpy Warning freql c 94 missing prototype for memcpy 0 errors 2 warnings Yes but where is memcpy defined We look at the documentation using F1 in Wedit and we find out that it needs the lt string h gt header file We recompile and we get H lcc examples gt lcc freql c Error freql c 95 type error in argument 1 to memcpy found struct _finddata_t expected pointer to void 1 errors O warnings Wow an error We look into the offending line and we see memcpy
472. put gt 9 1 ConstraintFailed _ func__ Input gt 9 NULL 1 13 38 Precedence of the different operators In their book C a reference manual Harbison and Steele propose the following table Tokens Operator Class Precedence Associates names literals simple tokens primary 16 n a a k subscripting postfix 16 left to right f function call postfix 16 left to right point direct selection postfix 16 left to right gt indirect selection postfix 16 left to right increment decrement postfix 16 left to right type name init compound literal postfix 16 left to right increment decrement prefix 15 right to left sizeof size unary 15 right to left bitwise not unary 15 right to left logical not unary 15 right to left arithmetic negation plus unary 15 right to left amp address of unary 15 right to left 74 C programming with Icc win32 indirection unary 15 right to left type name casts unary 14 right to left x S multiplicative binary 13 left to right additive binary 12 left to right lt lt gt gt left right shift binary 11 left to right lt gt lt gt relational binary 10 left to right equal not equal binary 9 left to right amp bitwise and binary 8 left to right A bitwise xor binary 7 left to right bitwise or binary 6 left to right amp amp logic
473. quite ugly and may be non portable to other systems where the conventions for dynamically linked code may be completely different A definitions file spares us to hard wire that syntax in the source code The definitions file has its drawbacks too however We need yet another file to maintain another small thing that can go wrong For our example we will use the __declspec dllexport syntax since we have only one function to export We return to our library project and reopen it We go again to the linker configuration tab that now is called librarian since we are building a static library and we check the radio button corresponding to a DLL project We answer yes when Wedit says whether it should rebuild the makefile and there we are Now we have to make the modifications to our small library We have to define a function that will be called when the library is loaded Traditionally the name of this function has been LibMain since the days of Windows 3 0 or even earlier We stick to it and define the following function int WINAPI LibMain HINSTANCE hDLLInst DWORD Reason LPVOID Reserved switch Reason 114 You can change this by pressing the corresponding button in the linker configuration tab or by giving the argument nounderscores to the linker when building the DLL 252 C Tutorial case DLL_PROCESS_ATTACH hinst hDLLInst DoRegisterClass break
474. r a lot of errors during the compilation instead of crashing at run time when an operation with incompatible types is attempted 1 6 1 What is a type A first tentative definition for what a type is could be a type is a definition of an algorithm for understanding a sequence of storage bits It gives the meaning of the data stored in mem ory If we say that the object a is an int it means that the bits stored at that location are to be understood as a natural number that is built by consecutive additions of powers of two If we say that the type of a is a double it means that the bits are to be understood as the IEEE 754 standard sequences of bits representing a double precision floating point value Functions have a type too The type of a function is determined by the type of its return value and all its arguments The type of a function is its interface with the outside world its inputs arguments and its outputs return value Types in C can be incomplete i e they can exist as types but nothing is known about them neither their size nor their bit layout They are useful for encapsulating data into entities that are known only to certain parts of the program Each type can has an associated pointer type for int we have int pointer for double we have double pointer etc We can have also pointers that point to an unspecified object They are written as void i e pointers to void In a similar manner we can derive a functi
475. r returned Size of the returned A byte pointer to the message DWORD cbhEncodedBlob pbEncodedBlob pbContent BYTE src content cbContent SrO count Get the size of the encoded message BLOB of messag Message encoding type Pointer to structure Inner content object ID cbEncodedBlob CryptMsgCalculateEncodedLength MY_ENCODING_TYPE 0 Flags CMSG_DATA Message type NULL NULL cbContent if cbEncodedBlob Size of conten return 0 Allocate memory for the encoded BLOB pbEncodedBlob BYTE Open a message to encod hMsg CryptMsgOpenToEncode 0 r MY_ENCODING_TYP Flags allocate_proper_space cbEncodedBlob 1 1 GI Encoding type 384 C Tutorial CMSG_DATA Message type NULL Pointer to structure NULL Inner content object ID NULL if hMsg return 0 Update the message with the data if CryptMsgUpdate hMsg Handle to the message pbContent Pointer to the content cbContent Size of the content TRUE Last call return 0 Get the resulting message if CryptMsgGetParam hMsg Handle to the message CMSG_BARE_CONTENT_PARAM Parameter type 0 Index pbEncodedBlob Pointer to the BLOB amp cbEncodedBlob Size of the BLOB return 0 pbEncodedBlob now points to the encoded signed c
476. r the Blaster worm Here is the code that allowed the Blaster worm to exist 2 HRESULT GetMachineName WCHAR pwszPath WCHAR wszMachineName N 1 LPWSTR pwszServerName wszMachineName while pwszPath L pwszServerNamet pwszPathtt The error here is the assumption that the path is a reasonable path that will not overrun the des tination buffer Machine names are normally at most 10 15 chars long If you are not expect ing unreasonable input you can just use the above code And that code was running for quite a long time before this time bomb exploded and a clever hacker found out that he she could gain control of the machine with this sloppy programming snippet 1 2 4 Watch out for trojans The windows API CreateProcess can be given the name of the program to execute in two ways as its first argument or as a whole command line in its second parameter leaving the first empty as NULL Suppose this CreateProcess NULL C Program Files myprogram exe Suppose now that somebody has left a c program exe executable in the right place What will happen CreateProcess will start executing c program instead of the indicated pro gram A simple way to avoid this is to enclose the name of the program in quotes CreateProcess NULL C Program Files myprogram exe K F Notice that the related API WinExec will scan its input for the first space making it worst than CreateProces
477. r true or false depending if the user has pressed OK or can celled the operation If the user pressed OK we would find the string that was entered in the buffer that we pass to GetString To avoid any overflow problems we would pass the length of the character string buffer so that the GetString routine stops input when we reach that limit The C language supports code reuse You can compile code that is useful in many situations and build libraries of routines that can be reused over and over again The advantages are many e The code has to be written once and debugged once e The size of our program stays small since we call a routine instead of repeating the code all over the place Function calls are the mechanism of code reuse since a function can be used in many situa tions Libraries are just a collection of routines that are linked either directly or indirectly with the main program From the standpoint of the user of the library not the one who is building it the usage is quite simple 1 You have to include the header file of the library to make the definition available to the compiler 2 You use the functions or data 3 You add the library to the set of files that the linker uses to build your program This simplicity of usage makes libraries a good way to reuse and share the code between dif ferent applications Under windows we have two types of libraries 246 C Tutorial Static libraries These libraries a
478. r will contain whatever was in there when the compiler allocated the stack frame Note that many other compilers do not do this and some programs run without crashing out of sheer luck Since Icc win catches this error it looks to the users as if the compiler was buggy I have received a lot of complaints because of this This kind of problem is one of the most common bugs in C Forgetting to initialize a pointer is something that you can never afford to do Another error is initializing a pointer within a conditional expression char BuggyFunction int a A closer view 73 char result if a gt 34 result malloc at34 return result If the argument of this function is less than 35 the pointer returned will be a dangling pointer since it was never initialized 1 13 37 Predefined identifiers A very practical predefined identifier is___ fuunc___ that allows you to obtain the name of the current function being compiled Combined with the predefined preprocessor symbols LINE__ and__ FILE___ it allows a full description of the location of an error or a poten tial problem for logging or debug purposes An example of the usage of those identifiers is the macro require that tests certain entry conditions before the body of a function define require constraint constraint 1 ConstraintFailed _ func _ constraint NULL For instance when we write require Input gt 9 we obtain In
479. ram to test our dll testdialog but instead of the execution of the program we see a dialog box like this testdialog exe Unable To Locate DLL x The dynamic link library dialog dll could not be found in the specified path D lec examples dialog C WINNT System32 C WINNT system C WINNT C AWINNT system32 C WINNT h Mec bin h msdev bin c ntreskit k ste xmf miktex bin h msdev bin e perform include e smalleiffel bin k borland bec55 bin d iec bin c common The system tells us that it can t find the dll Well if you reflect about this this is quite normal A DLL must be linked when the execution of the program starts The system will search in the start directory of the program and in all directories contained in the PATH environment variable If it doesn t find a dialog dll any where it will tell the user that it can t execute the program because a missing DLL that s all The solution is to copy the DLL into the current directory or copy the DLL in one of the direc tories in your PATH variable Another solution of course is to go to the directory where the DLL is and start execution of the program there Usinga DLL 255 This dependency on the DLL is quite disturbing All programs that use the DLL in this fashion would need to have the DLL in their startup directory to be able to work at all A way to get rid of this is to avoid linking with the DLL import library Yes you will say but how
480. rd with specific messages when a key is pressed released repeat counts and all the keyboard has to offer Here is a small description of each Message WM_ACTIVATE Meaning Window is being either activated or desactivated WM_CHAR The user has typed a character Here you receive characters like m for instance WM_KEYDOWN A key has been pressed Here you can use keys like the arrows of the keyboard Del Insr etc WM_KEYUP A key has been released 2 8 7 Handling moving resizing You get WM_MOVE when your window has been moved WM_STZE when your window has been resized In the parameters of those messages you find the new positions or new size of your window You may want to handle those events when you have child windows that you should move with your main window or other measures to take depending on your applica tion Message Meaning WM_MOVE Sent after a window has been moved WM_MOVING Sent to a window when the user is moving it By pro cessing this message you can monitor the position of the drag rectangle and if needed change its position 268 C Tutorial Message Meaning WM_SIZE Sent after a window has been resized WM_SIZING Sent to a window that the user is resizing By process ing this message an application can monitor the size and position of the drag rectangle and if needed change its size or po
481. rdList int Count struct _WordList Next char Word WORDLIST We have an integer that holds the number of times this word appears in the text a pointer to the next word in the list and an unspecified number of characters just following that pointer This is a variable sized structure since each word can hold more or less characters Note that variable sized structures must have only one flexible member and it must be at the end of the definition Our EnterWord function can look like this void EnterWord char word int h hash word Get the hash code for this word WORDLIST wl WordTable h Index the list at that slot while wl Go through the list if strcmp wl gt Word word wl gt Count Word is already in the table return increment the count and return wl wl gt Next Go to the next item in the list Here we have a new word since it wasn t in the table Add it to the table now wl NewWordList word wl gt Next WordTable h WordTable h wl Counting words 155 What would be a good hash function for this application This is a tutorial so we keep things simple Here is a very simple hash function int hash char word int h 0 while word h word word return h amp Oxffff We just add up our characters If we get a hash value of more than 65535 the size of our table we just take the lower 16 bits of the hash value
482. re built in files that normally have the lib extension and are linked with the program directly i e they are passed to the linker as arguments The linker takes the code of the needed functions from the library and copies the code into the pro gram Dynamic libraries These aren t copied into the main program but are resolved at load time by the program loader When you double click a program s icon you activate a system pro gram of windows called program loader that goes to the disk finds the code for the execut able you have associated with the icon and loads it from disk into RAM When doing this the loader finds if the program needs any dynamic libraries that normally have the DLL extension and reads their code too linking it dynamically to the program being loaded Which one should we use in this application Static or not static That is the question Our program needs a class registration before it can call the DialogBoxParam API If we use the static library approach we would have to require that the user of the library calls some ini tialization routine before to allow us to register our class with windows But this would complicate the interface We introduce with this requirement yet another thing that can go wrong with the program yet another thing to remember A way out of this dilemma would be to take care of doing the registration automatically We could setup an integer variable that would start as zero Before
483. re information read the associated documentation for the functions given here Etc 317 One thing you will wonder is how do you get a HANDLE starting with a FILE pointer We Function name Description CreateFile Opens or creates a file It can open a COM port serial communica tions or a pipe CloseHandle Use it to close a file ReadFile or ReadFi Reads data from a file starting at the current file pointer Both syn leEx chronous and asynchronous versions exist WriteFile or Write Writes data to a file starting at the current file pointer Both syn FileEx chronous and asynchronous versions exist CopyFile or CopyFi Copy one file to another leEx MoveFile or Move FileEx Moves a file DeleteFile Deletes a file GetFileAttributes or Reads the file attributes like if its read only hidden system etc GetFileAttributesEx SetFileAttributes or Sets the file attributes SetFileATtributesEx GetFileSize Returns the size of a file FindFirstFile and Searches for a file matching a certain wildcard FindNextFile discussed above files and used always a FILE structure as specified in lt stdio h gt To obtain a HANDLE that can be used with the windows file functions you write include lt windows h gt include lt stdio h gt FILE fptr HANDLE h HANDLE _get_osfhandle _fileno fptr 2 17 4 These days files are taken for granted Fil
484. re it is used 2 The code is easier to read 3 He argued that what Mr Twink proposed are just micro optimizations that do not change at all the actual speed of the program Mr Heathfield calculated that a user working non stop using his program 24 24 7 7 would need 50 years to get the time spent in typing the routine anew Now dear reader it is up to you to make up your mind 224 C programming with Icc win32 1 4 FunwithC There are countless ways of writing strange programs in C Here are some of them that I have collected surfing the net 1 4 1 Calculating pi This program will print the first few hundred digits of pi Do not ask me how it works I found it in http paul rutgers edu rhoads Code pi c int a 10000 b c 2800 d e 2801 g int main void for b c f b a 5 for d 0 g c 2 c 14 printf 4d etd a e d a for b c d f b a f b d g d g b d b 1 4 2 Writing poetry This one will write the 12 verses of the 12 Days of Christmas include lt stdio h gt main t _ a char a return 0 lt t t lt 3 main 79 13 at tmain 87 1 _ main 86 0 at1 a 1 t lt _ main t 1 _ a 3 main 94 27 t a amp amp t 2 _ lt 13 main 2 _ 1 s d d n 9 16 t lt 0 t lt 72 main _ t Qn wt witcdnr xr de w wkqtnt 1 n nt nt a n k r d 3 wtK w K e dq l qt d K k q r eKK w r eKK
485. rently by the software after all But this is no longer C is the heart of the application True there are other languages that let you specify with greater richness of rules what and how can be sub classed and inherited C allows you to do anything there are no other rules here other the ones you wish to enforce You can subclass a structure like this You can store the current pointer to the procedure some where and put your own procedure instead When your procedure is called it can either Do some processing before calling the original procedure Do some processing after the original procedure returns Do not call the original procedure at all and replace it entirely We will show a concrete example of this when we speak about windows sub classing later Sub classing allows you to implement dynamic inheritance This is just an example of the many ways you can program in C But is that flexibility really needed Won t just bool UpdateBalance struct customer pCustomer double newBalance do it too Well it depends Actions of the general procedure could be easy if the algorithm is simple and not too many special cases are in there But if not the former method even if more compli cated at first sight is essentially simpler because it allows you greater flexibility in small man ageable chunks instead of a monolithic procedure of several hundred lines full of special case code Mixed strategies are possible You leave for
486. ression is executed In the code fragment array 234 678 a tarray 234 The integer a and the array element at the 234th position will both have the value 679 When applied to pointers these operators increment or decrement the pointer to point to the next or previous element Note that if the size of the object those pointers point to is different than one the pointer will be incremented or decremented by a constant different than one too NOTE Only one postfix expression is allowed for a given variable within a statement For instance the expression i i is illegal C and will never work the same from one compiler to the next or even within the same compiler system will change depending whether you turn optimizations on or off for instance The same applies for the decrement operator i i is also illegal Note that this holds even if the expression is much more complicated than this i MyTable i Field gt table i is completely illegal C 1 13 10 Conditional operator The general form of this operator is expressionl expression2 expression3 41 Add the overflowcheck option to the command line 58 C programming with Icc win32 The first operand of the conditional expression expression1 is evaluated first The sec ond operand expressionz2 is evaluated only if the first compares unequal to 0 the third operand is evaluated only if the first compares equal to 0 the result of th
487. ressiveness by reducing the severity of name clashes two different libraries can use the same identifier if they use different arguments for that action 3 It makes understanding of the action being performed easier Aha It is summing all elements of the vector 1 36 3 2 Disadvantages of overloading functions or operators 1 It does little to improve the generality of the code For instance to correctly define a min overloaded function an unbounded number of implementations are necessary each one for each numeric type 2 It is unconstrained by nature No guarantee is given that all the different implementations implement the same notion hence a small programmer error can result in a call to a routine that does a completely different thing 3 It makes detailed understanding of the action being performed more difficult What is the function being called here Yes it is adding something but HOW 1 36 4 Default arguments Default arguments allow you to simplify the interface of a function by providing arguments that if not present will assume a default value For instance int fn int a int b 78 This declares a function called fn that takes one argument and optionally a second When the second is not given the compiler will arrange for it being 78 For instance fn 2 is equivalent to fn 2 78 1 36 5 Structured exception handling 1 36 5 1 Why exception handling As you know very well the following
488. rgv 2 3 h _findfirst Path amp fd A if h 1 fprintf stderr No files match s n Path return 1 matches 0 do p strrchr Path if p p 0 strcat Path fd name matches processfile expression Path while _findnext h amp fd 0 _findclose h The libraries of Icc win 211 if matches printf d matches n matches return matches 1 We do not do an extensive error checking in this function to keep things simple but a min imum should be done We test the format of the arguments since it is pointless to go on if this data is absent 2 It is more efficient to compile once for all the regular expression into its internal form If the compilation fails this means that the regular expression was incorrect and we exit with an error 3 Now we start a quite messy path handling stuff We test first if the path we have received is an absolute path i e a path like c mydir myprograms ora path that starts at the root of the current drive like mydir myprograms There is a function for this in the Windows API PathIsRoot but I have seen it fail for mysterious reasons so we use a rather crude algorithm if the second character of the path is a or the first character is a V we have an absolute path Note that there can t be any buffer overflow here since if we have a path of only one character the second one will be the terminatin
489. riable Another reason to stick to Icc win Using arrays and sorting 103 arrays and pointers to the first member are equivalent This means that in many situations arrays decay into pointers to the first element and loose their array ness That is why you can do in C things with arrays that would never be allowed in another languages At the end of this tutorial we will se how we can overcome this problem and have arrays that are always normal arrays that can be passed to functions without losing their soul At last we are ready to call our famous qsort function We use the following call expression qsort void argv size_t argc sizeof char compare The first argument of qsort is a void Since our array argv is a char we transform it into the required type by using a cast expression void argv The second argument is the number of elements in our array Since we need a size_t and we have argc that is an integer variable we use again a cast expression to transform our int into a size_t Note that typedefs are accepted as casts The third argument should be the size of each element of our array We use the built in pseudo function sizeof which returns the size in bytes of its argument This is a pseudo function because there is no such a function actually The compiler will replace this expression with an integer that it calculates from its internal tables We have here an array of char so we just tell the c
490. riable names automatically and other more or less obscure hacks 1 34 1 5 The operator This operator converts the given token into a character string It can be used only within the body of a macro definition After defining a macro like this define toString Token Token an expression like toString MyToken will be translated after preprocessing into MyToken An example of its use is the following situation We have a structure of an integer error code and a character field containing the description static struct table unsigned int code unsigned char desc hresultTab Then we have a lot of error codes defined with the preprocessor ELUNEXPECTED E_NOTIMPL E_INVALIDARG etc We can build a table with hresultTab Table E_UNEXPECTED E_UNEXPECTED E_NOTIMPL E_NOTIMPL etc This is tedious and there is a big probablity of making a typing mistake A more intelligent way is define CASE a a a Now we can build our table like this hresultTab Table CASE E_UNEXPECTED CASE E_NOTIMPL 1 34 2 Things to watch when using the preprocessor 1 One of the most common errors is to add a semi colon after the macro define add a b a b When expanded this macro will add a semicolon into the text with the consequence of a cascade of syntax errors with apparently no reason A closer look at the pre processor 173 2 Watch for side effects within macros A macro invocation is similar
491. ribed in more detail in the technical documentation Here we just tell you the main steps e The source file is first pre processed The include directives are resolved and the text of the included files is inserted into the source file The result of this process can be seen if you call the compiler with the E flag For instance to see what is the result of pre processing the hello c file you call the compiler in a command shell window with the command line Lcc E hello c The resulting file is called hello 1 e The front end of the compiler proper processes the resulting text Its task is to generate a series of intermediate code statements Again you can see the intermediate code of Icc by calling the compiler with Lcc z hello c This will produce an intermediate language file called he Llo 1il that contains the intermediate language statements e The code generator takes those intermediate instructions and emits assembler instructions from them Assembly code can be generated with the Lcc S hello c command and the generated assembly file will be called he llo asm The generated file contains a listing of the C source and the corresponding translation into assembly language e The assembler takes those assembly instructions and emits the encodings that the integrated circuit can understand and packages those encodings in a file called object file that has the obj extension This file is passed then possibly with other object files
492. right after the fopen call We can read characters from a file using the fgetc function That function updates the current position i e the position where the next character will be read 57 Global variables provoke an undocumented coupling between several apparently unrelated procedures or modules Overuse of them is dangerous and provokes errors that can be difficult to understand and get rid of I learned this by experience in long debugging sessions and now I use global variables more sparingly Using arrays and sorting 99 But let s come back to our task We update the array at each character within the while loop We just use the value of the character that must be an integer from zero to 256 anyway to index the array incrementing the corresponding position Note that the expression Frequencies count means Frequencies count Frequencies count 1 1 e the integer at that array position is incremented and not the count variable Then at the end of the while loop we display the results We only display frequencies when they are different than zero i e at least one character was read at that position We test this with the statement if Frequencies count 0 statements The printf statement is quite complicated It uses a new directive c meaning character and then a width argument i e 3c meaning a width of three output chars We knew the d directive to print a number but now it is augme
493. ritten 13 Choose another name like dialogs c for instance 132 Look in the weditreslib folder The file commmsg c contains the default procedure and all the machinery necessary for the run time of the framework Using the graphical code generator 297 Now when you save your work all the dialog procedures will be written for you But before we have to tell the framework several things The first will be the prefix to use for all the procedures that will be used in this dialog box We define this in the main properties dialog box obtained when you double click in the dialog title D1g400 is an automatic generated name not very convincing We can put in there a more meaningful name like DlgSearch for instance We will see shortly where this name is used What we want to do now is to specify to the editor where are the events that interest us For each of those events we will specify a callback procedure that the code generated by the editor will call when the event arrives Basically all frameworks no matter how sophisticated boil down to that a quick way of specifying where are the events that you want to attach some code to The events we can choose from are in the properties dialog boxes associated with each ele ment of the dialog box You have the general settings in the properties window associated with the dialog box that appears when you double click in the title and you have the buttons prop erties that
494. rn TRUE return FALSE A dialog box procedure is called by the system It has then a fixed argument interface and should return a predefined value It receives from the system the handle of the dialog box win dow the message and two extra parameters Normally these procedures are a big switch statement that handles the messages the program is interested in The return value should be TRUE if the dialog box procedure has handled the message passed to it FALSE otherwise The general form of a switch statement is very simple you have the switch expression that should evaluate to an integer and then you have several cases that should evaluate to com pile time constants All those names in the switch statement above are just integers that have been given a sym bolic name in windows h using the preprocessor define directive A break keyword sepa rates one case from the next one Note that in C a case statement can finish without a break keyword In that case execution continues with the code of the next case In any case of course a return statement finishes execution of that case since control is immediately passed to the calling function 108 238 C Tutorial In this procedure we are interested in only three messages hence we have only three cases in our switch 1 WM_INITDIALOG This message is sent after the window of the dialog box has been created but
495. rn a 64 bit integer please do not complain to me Note too the strange form of the error checking afterwards we check for a return value of all bits set to one and check the result of the GetLastError API SetLastError 0 1iSrcFileSize LowPart GetFileSize hSrcFile amp liSrcFileSize HighPart if OxFFFFFFFF 1liSrcFileSize LowPart amp amp GetLastError NO_ERROR printf couldn t get size of source file n goto DONE la Special case If the source file is zero bytes we don t map it because there s no need to and anyway CreateFileMapping cannot map a zero length file But since we ve created the destination we ve successfully copied the source if 0 liSrcFileSize QuadPart fResult SUCCESS goto DONE Map the source file into memory We receive from the OS a HANDLE that corresponds to the opened mapping object Y hSrcMap CreateFileMapping hSrcFile 0 PAGE_READONLY 0 0 0 if hSrcMap printf couldn t map source file n goto DONE 324 C Tutorial la Now we create a file mapping for the destination file using the size parameters we got above 7 hDstMap CreateFileMapping hDstFile 0 PAGE_READWRITE 1liSrcFileSize HighPart liSrcFileSize LowPart 0 if hDstMap DEBUG_PRINT couldn t map destination file n goto DONE la Now that we have the source and destination mapping objects we build two map views of the source an
496. ro are one we effectively turn off that bit only leaving all others untouched Customizing the wizard generated sample code 265 2 8 Customizing the wizard generated sample code The generator can be configured for different types of applications Use first the simple win dow application This setup produces a standard WinMain procedure like this You can add code for the initialization of your application in the InitApplication function The standard version just registers the class of the main window In the next paragraphs we will try to see how we modify this skeleton to add different items you may want to add to your application 2 8 1 Making a new menu or modifying the given menu Add your item with the resource editor and give it an identifier normally written in uppercase like IDMENU_ASK_PARAMETERS or similar This is surely not the text the user will see but a symbolic name for an integer constant that windows will send to the program when the user presses this option We can then continue our beloved programming traditions Once that is done and your menu displays correctly go to the wizard code in theMainWnd Proc function There you will see a big switch with different code to handle the events we are interested in The menu sends a command event called WM_COMMAND In there you see that this event will be handled by the HANDLE_COMMAND macro It is just a shorthand to break down the 64 bits that windows se
497. roduce approximations that can lead to errors truncation errors rounding errors whatever Suppose we want to evaluate exp x by using a series expansion 2 3 4 5 6 7 8 exp x aoe x ud zs a ama E E T 2 6 24 120 720 5040 40320 We have to stop somewhere No way out Here we get tired at the 9th term And no matter how much effort we put into this there will be always a truncation error In this case the truncation error can be accurately calculated Analyzing and estimating the error bounds is the art of numerical analysis Computers use bit patterns to represent any object that can be represented in a computer In the section about structures we represented a person by a bit pattern like this structure person char Name int age A person is surely not a bit pattern We use the bit pattern to abstract some characteristics of the person we are interested in Numbers aren t different They can be represented by a bit pat tern too We can use 32 bits what allows us to represented almost 4294967296 numbers But obviously there are more numbers infinitely more than that so any representation will always fail somewhere Any computation involving floating point numbers that map onto the real line as its argu ments can potentially produce a result that lies in between two floating point numbers In that case that number is rounded off to one of the grid points And this incurs round off error Any practical numerical ana
498. romotions are applied to each argument and float arguments are passed as double 1 13 6 Functions with variable number of arguments To use the extra arguments you should include lt stdarg h gt To access the additional argu ments you should execute the va_start then for each argument you execute a va_arg Note that if you have executed the macro va_start you should always execute the va_end macro before the function exits Here is an example that will add any number of integers passed to it The first integer passed is the number of integers that follow A closer view 55 include lt stdarg h gt int va_add int numberOfArgs va_list ap int n numberOfArgs int sum 0 va_start ap numberOfArgs while n sum va_arg ap int va_end ap return sum We would call this function with va_add 4s 987 876 567 9556 or va_add 2 456 789 1 13 6 1 Implementation details Under 32 bit systems linux or windows the variable arguments area is just a starting point in the stack area When you do a va_start ap the system makes to ap pointer point to the start of the arguments just after the return address Later when you retrieve something from the variable argument list this pointer is incre mented by the size of the argument just being passed in and rounded to point to the next This is quite simple and works in many systems Other systems specially windows 64 bits or Linux 6
499. ror found expecting Warning args c 6 Statement has no effect Error args c 6 syntax error found expecting Error args c 6 illegal statement termination Error args c 6 skipping 6 errors 1 warnings D lcc examples gt We see here a chain of errors provoked by the first The compiler tries to arrange things by skipping text but this produces more errors since the whole for construct is not understood Error recovering is quite a difficult undertaking and Icc win isn t very good at it So the best thing is to look at the first error and in many cases the rest of the error messages are just con sequences of it 3 Another type of errors can appear when we forget to include the corresponding header file If we erase the include lt stdio h gt line in the args program the display looks like this D lcc examples gt lcc args c Warning args c 7 missing prototype for printf 0 errors 1 warnings This is a warning The printf function will be assumed to return an integer what in this case is a good assumption We can link the program and the program works It is surely NOT a good practice to do this however since all argument checking is not done for unknown func tions an error in argument passing will pass undetected and will provoke a much harder type of error a run time error In general it is better to get the error as soon as possible The later it is discovered the more difficult it is to find
500. royed anyway 2 8 5 Getting mouse input You can handle the WM_LBUTTONDOWN or WM_RBUTTONDOWN messages To follow the mouse you handle the WW_MOUSEMOVE messages In the information passed with those mes sage parameters you have the exact position of the mouse in pixel coordinates Message Meaning Customizing the wizard generated sample code 267 W BUTTONBDBLCLK Double click in left mouse button WM_LBUTTONDOWN WM_LBUTTONUP Left mouse button click For the middle and right button the messages used use the letters M and R instead of L here WM_MOUSEWHEEL The mouse wheel has been used WM_MOUSEMOVE This is posted to a window when the cursor moves If the mouse is not captured the message is posted to the window that con tains the cursor Otherwise the message is posted to the window that has captured the mouse WM_MOUSEHOVER This is posted to a window when the cursor hovers over the cli ent area of the window for the period of time specified in a prior call to TrackMouseEvent WM_MOUSELEAVE This is posted to a window when the cursor leaves the client area of the window specified in a prior call to TrackMou seEvent 2 8 6 Getting keyboard input Handle the WM_KEYDOWN message or the WM_CHAR message Windows allows for a fine grained control of the keyboa
501. rrent time adjusts hours and minutes sets system time 2 21 23 Getting the list of running processes You can use pdh lib to get a list of all the running processes here is a simple code that will print this list in the standard output JS Using pdh lib to get a list of the running processes This sample is adapted from the similar sample code in the windows SDK Compile with Ic listproc c pdh lib j Finclude lt windows h gt Finclude lt winperf h gt include lt malloc h gt Finclude lt stdio h gt Hinclude lt pdh h gt Hinclude lt pdhmsg h gt int main void PDH_STATUS pdhStatus ERROR_SUCCESS LPTSTR szCounterListBuffer NULL DWORD dwCounterListSize 0 LPTSTR sziInstanceListBuffer NULL DWORD dwinstanceListSize 0 LPTSTR szThisInstance NULL call the function to determine the required buffer size for the data pdhStatus PdhEnumObjectItems NULL reserved NULL local machine Process object to enumerate szCounterListBuffer pass in NULL buffers amp dwCounterListSize an 0 length to get szInstanceListBuffer required size amp dwinstanceListSize of the buffers in chars PERF_DETAIL WIZARD counter detail level 0 if pdhStatus ERROR_SUCCESS amp amp pdhStatus PDH_MORE_DATA printf nUnable to determine the buffer size required return 1
502. rs with enough characters inside to hold a maximum path and a few more Then and in the same declaration we declare a character pointer p This pointer will be set with strrchr If there isn t any backslash in the path we just set the start of our full name to zero If there is a path we cut the path component as we did before and copy the path component into the fullname variable The library function strcpy will copy the second argument to the first one including the null character for terminating correctly the string Buffer overflows 135 We add then a backslash using the strcat function that appends to its first argument the second string It does this by copying starting at the terminator for the string and copying all of its second argument including the terminator We restore the string and append to our full path the given name In our example we copy into fullpath the character string src77 then we add the backslash and then we add the rest of the name to build a name like src77 alloc c This done we look again into our program Yes there are things that could be improved For instance we use the 256 to write the number of elements of the array Frequencies We could improve the readability of we devised a macro NELEMNTS that would make the right calcula tions for us That macro could be written as follows define NELEMENTS array sizeof array sizeof array 0 This means just that th
503. rs in HKEY_CLASSES_ROOT and in process servers are registered in this key To change the settings for the interactive user store the changes under HKEY_CURRENT_USER Software Classes rather than HKEY_CLASSES_ROOT 2 HKEY_CURRENT_USER Registry entries under this key define the preferences of the current user These preferences include the settings of environment variables data about program groups colors printers network connections and application preferences This key makes it easier to establish the current user s settings the key maps to the current user s branch in HKEY_USERS In HKEY_CURRENT_USER software vendors store the current user specific preferences to be used within their applications Lcc win for example creates the HKEY_CURRENT_USER Software lcc key for its applications to use with each application creating its own subkey under the Icc key 3 HKEY_LOCAL MACHINE Registry entries under this key define the physical state of the computer including data about the bus type system memory and installed hardware and software It contains subkeys that hold current configuration data including Plug and Play information the Enum branch which includes a complete list of all hardware that has ever been on the system network logon preferences network security information The Registry 309 software related information such as server names and the location of th
504. ry clever This can be solved by adding a line like this pLink gt SetWorkingDirectory c my documents lcc myproject References IShellLink Interface documentation 2 19 Error handling under windows The windows API is an ancient software construct Pieces of the original design started with windows 2 x under MSDOS with the 64K limitations of real mode are still buried within it Pieces of the Windows 3 1 16 bit protected mode software are still very much in evidence and the Win32 API is already 8 years old and counting Because those historical reasons there exists a bewildering set of failure results We have actually all possibilities 37 1 The boolean convention Returning TRUE for success FALSE for failure This is a simple minded approach that is used in many APIs You code then if DoSomething failure handling The drawback of this convention is that with only two different values there is no room for explaining the failure reasons 2 The status convention Returning a status like HRESULT A HRESULT gt 0 such as S_OK is a success and a HRESULT lt 0 such as E_FATL is a failure This would be OK but there is the problem that other API functions return an error code defined in windows h There is the BIG problem that ERROR_SUCCESS 8 is defined there as zero In this schema the value zero is reserved to indicate that everything is OK and all other values 137 This part has been adap
505. ry functions instead of writing your own The isalpha function does not make any jumps like we do but indexes a table of property bits Much faster And what about error checking Remember we just open the file given in the command line without any test of validly We have to fix this Another useful feature would be to be able to report a line number associated with our file instead of just an error message that leaves to the user the huge task of finding where is the offending part of the input file that makes our program crash This is not very complex We just count the new line characters The output of our program is far from perfect It would be better if we justify the columns To do that we have to just count the length of each word and keep a counter to the longest word we find Another nice thing to have would be a count of how many words with 1 character we find how many with two etc In the Appendix you will find the complete source code containing the answers to this prob lem 1 32 Time and Date functions The C library offers a lot of functions for working with dates and time The first of them is the time function that returns the number of seconds that have passed since January first 1970 at midnight 78 Several structures are defined that hold time information The most important from them are the tm structure and the timeb structure struct tm int tm_sec int tm min int tm_hour 78
506. s NO_ERROR printf tError d getting stats n GetLastError return 1 printf tNumber of IP addresses ld n pStats gt dwNumAddr printf tNumber of Interfaces ld n pStats gt dwNumIf printf tReceives ld n pStats gt dwInReceives printf tOut Requests ld n pStats gt dwOutRequests printf tRoutes ld n pStats gt dwNumRoutes printf tTimeout Time ld n pStats gt dwReasmTimeout printf tIn Delivers ld n pStats gt dwInDelivers 398 C Tutorial printf tIn Discards ld n pStats gt dwInDiscards printf tTotal In ld n pStats gt dwInDelivers pStats gt dwInDiscards printf tIn Header Errors ld n pStats gt dwInHdrErrors Get the TCP statistics MIB_TCPSTATS pTCPStats pICcPStats MIB_TCPSTATS malloc sizeof MIB_TCPSTATS if dwRetVal GetTcpStatistics pTCPStats NO_ERROR printf Error d getting TCP Stats n GetLastError printf tActive Opens ld n pTCPStats gt dwActiveOpens printf tPassive Opens ld n pTCPStats gt dwPassiveOpens printf tSegments Recv ld n pTCPStats gt dwiInSegs printf tSegments Xmit ld n pTCPStats gt dwOutSegs printf tTotal Conxs ld n pTCPStats gt dwNumConns Getting accurate information about the TCP and IP statistics is very important when you want to measure the performance of a
507. s i e a standardized exchange between two computers Within a HTTP transaction you exchange information with another computer elsewhere on a network The information exchanged can be a file that contains data in the form of text sound video or whatever or it can be the results of a database query A piece of information exchanged over a network is called a resource Normally the computer that sends a resource is the server and the computer that receives that resource is a client The process of obtaining a resource using the HTTP protocol requires that a series of mes sages be exchanged between the client and the server The client begins the transaction by sending a message that requests a resource This message is called an HTTP request or some times just a request An HTTP request consists of the following components 1 Method Uniform Resource Identifier URI protocol version number 2 Headers 3 Entity body The request is sent as plain text over the network It uses the TCP IP port 80 The HTTP Protocol 389 When a server receives a request it responds by sending a message back to the client The message sent by the server is called an HTTP response It consists of the following compo nents 1 Protocol version number status code status text 2 Headers 3 Entity body The response either indicates that the request cannot be processed or provides requested infor mation Depending on the type of request this can be
508. s In the above example the code WinExec C program files myprogram exe will always try to execute c program if it exists 92 Microsoft Security Bulletin MS03 026 Buffer Overrun In RPC Interface Could Allow Code Execu tion 823980 Originally posted July 16 2003 Revised September 10 2003 Cited by Michael Hor ward in his excellent series about security in msdn The URL for one of its articles is http msdn microsoft com library default asp url library en us dncode html secure09 112003 asp 216 C programming with Icc win32 1 3 Pitfalls of the C language Look I am not a religious person C is not a religion for me and this means that I see some of the pitfalls of the language I write this so that you see them at the start and they do not bite you 1 3 1 Defining a variable in a header file If you write static int foo 7 in a header file each C source file that includes that header will have a different copy of foo each initialized to 7 but each in a different place These variables will be totally unrelated even if the intention of the programmer is to have a single variable foo If you omit the static at least you will get an error at link time and you will see the bug Golden rule Never define something in a header file Header files are for declarations only 1 3 2 Confusing and If you write if a 6 you are assigning to a the number 6 instead of tes
509. s lpPoints LPPOINT GlobalAlloc GPTR sizeof POINT iNumPts if lpPoints return FALSE Allocate room for the point types lpTypes GlobalAlloc GPTR iNumPts if lpTypes GlobalFree lpPoints return FALSE Get the points and types from the current path iNumPts GetPath hDC lpPoints lpTypes iNumPts More error checking if iNumPts 1 GlobalFree lpTypes GlobalFree lpPoints return FALSE Intialize the rectangle SetRect lprc OxFFFFF OxFFFFF 0 0 2 22 8 How do I close an open menu To cancel an active menu send a WM_CANCELMODE message to the window that owns it When you send the WM_CANCELMODE message to the owner window of an active menu the window exits the menu mode You can use this technique to force the abandonment of active TrackPopupMenu or TrackPopupMenuEx 2 22 9 How do I center a dialog box in the screen To center a dialog box on the screen before it is visible add the following lines to the process ing of the WM_INITDIALOG message 360 C Tutorial RECT rc GetWindowRect hDlg amp rc SetWindowPos hDlg NULL GetSystemMetrics SM_CXSCREEN rec right rce left GetSystemMetrics SM_CYSCREEN rc bottom re top 0 0 SWP_NOSIZE SWP_NOACTIVATE dy 2 2 r This code centers the dialog horizontally and vertically 2 22 10 How do I create non re
510. s are performed between two operands of integer type The type of the result is deter mined by the type of the left operand Supposing 32 bit integers the operation int a 4976 int b a lt lt 3 consists of 1 0011 0111 0000 4976 1001 1011 1000 0000 39808 This is the same than 4976 8 39808 since 8 is 23 A shift to the left is equal to multiplying by 2 a shift to the right is equivalent to dividing by two Obviously if you make shifts bigger than the number of bits in the integer you are shifting you get zero This snippet include lt stdio h gt int main void int a 4977 int b 4977 int i for i 0 i lt 5 i printf 4977 lt lt d 8d 0x 08x n i a lt lt i a lt lt i printf 4977 lt lt Sd 8d 0x 08x n i b lt lt i b lt lt i produces the following output 4977 lt lt 0 4977 0x00001371 4977 lt lt 0 4977 Oxffffec8Ff 4977 lt lt 1 9954 0x000026e2 4977 lt lt 1 9954 0Oxffffd9le 4977 lt lt 2 19908 0x00004dc4 4977 lt lt 2 19908 Oxffffb23c 4977 lt lt 3 39816 0x00009b88 4977 lt lt 3 39816 Oxffff6478 4977 lt lt 4 79632 0x00013710 4977 lt lt 4 79632 Oxfffec8F 0 We have shifted a nibble 4 bits We see it when we compare the last two lines with the first ones The standard specifies that a right shift with a negative number is implementation defined It can be that in another machine you would get different res
511. s could be done with DLLs too the linker should export all externally visible symbols In practice is better only to export symbols that should be visible This avoids name clashes 250 C Tutorial When we start this program from the command line we see cc examp es dialog ccstestdialog this is the string This isn t that bad for a start We have a sophisticated line editor complete with arrow inter face to move around in the text clipboard support built in delete and backspace keys already taken care of etc If we would have to write ourselves an equivalent program it would cost us probably days of development To develop the clipboard interface already is quite a challenge But we are confronted to the problem of resources Our static library idea was a dead end We have to find something else Summary The C language supports the concept of code reuse in the form of libraries The static libraries are combined with the main application at link time statically They can t contain resources Dynamically linked libraries DLLs 251 2 4 Dynamically linked libraries DLLs A dynamically linked library is just like a static library it contains a set of useful functions that can be called from other software As with normal lib libraries there is no main function Unlike static libraries however they have several features that make them a very interesting alternative to static libraries e When they are load
512. s function in the Windows documentation of Icc win 2 22 21 initialize in WM_CREATE but the values of my variable change Why Consider this code snippet switch iMsg case WM_CREATE Pole 10 10 1 return 0 case WM_PAINT hdc BeginPaint hwnd amp ps GetClientRect hwnd amp rect int x y for x 0 x lt 20 x for y 0 y lt 20 ytt DrawBitmapNum hdc hBitmap rect left x 16 rect topty 16 Pole x yl l 8 EndPaint hwnd amp ps return 0 case WM_DESTROY PostQuitMessage 0 return 0 139 1 got the idea of this from http www kbcafe com articles HowTo Shell pdf by by Randy Charles Morin 372 C Tutorial The programmer initializes the array Pole first when it handles the creation message And the programmer expects that the value will stay from one invocation of this function to the next This will NOT be the case unless the variable is declared with the static keyword Only then values will be preserved from one call to the next and this becomes correct code This is a very common error 2 22 22 How do I translate between client coordinates to screen coordinates To determine the screen coordinates for the client area of a window call the ClientToScreen function to translate the client coordinates returned by GetClientRect into screen coordinates The following code demonstrates how to use the two functions together RECT rMyRect
513. s h Characteristics of integer types iso646 h Alternative spellings for some keywords If you prefer writing the opera tor amp amp as and use this header limits h Size of integer types locale h Definitions for the formatting of currency values using local conven tions math h Mathematical functions setjmp h Non local jumps i e jumps that can go past function boundaries See page 85 signal h Signal handling See page 188 stdbool h Boolean type and values stddef h This file defines macros and types that are of general use in a program NULL offsetof ptrdiff_t size_t and several others stdint h Portable integer types of specific widths stdio h Standard input and output stdlib h Standard library functions string h String handling Here are defined all functions that deal with the standard representation of strings as used in C See Traditional string representa tion in C on page 130 stdarg h Functions with variable number of arguments are described here See page 54 time h Time related functions See page 158 tgmath h Type generic math functions wchar h Extended multibyte wide character utilities wctype h Wide character classification and mapping utilities 1 4 1 The stdheaders h include file Normally it is up to you to remember which header contains the declaration of which func tion This can be a pain and it is easy to confuse some header with another To avoid this ov
514. s initialize tables and do some setup before actually beginning the computation they want to perform The best is to collect all those ini tializations into a single procedure so that any new initializations aren t scattered all around but concentrated in a single function 8 void Initialize void for int i 0 i lt 256 i Frequencies i CharacterValue i Following our analysis of main we see that the next steps are the processing of the opened file We read a character and we update the Frequencies array Well this is a single task that can be delegated to a function a function that would need the opened file handle to read from and a Frequencies array pointer to be updated We develop a ProcessFile function as follows int ProcessFile FILE infile CHARS Frequencies int count 0 int c fgetc infile 68 Yes but then all initializations are done out of their respective contexts Some people say this is the wrong way to go and that each data type should initialize in a separate init procedure In this concrete example and in many situations making a global init procedure is a correct way of building software Other contexts may be different of course 69 We find very often the expression while c fgetc infile EOF instead of the expression above Both expressions are strictly equivalent since we first execute the fgetc function assigning the result to c
515. s into a bitmap with the colors translated according to a translation table This table is prepared in lines 12 to 17 then passed as argument to the API Now we have to create our memory device context We make a compatible context in line 19 and then select into it the bitmap we have just obtained after color translation We will use this memory bitmap to copy bits into our display Before that however we make a solid brush and fill the whole window with the background color lines 21 23 For each character in our text we do 1 Calculate a rectangle with the position in our memory bitmap of the bits of the given character Since we assume that all characters have the same width it is a simple multiplication of a known constant by the width of the characters We leave that calculation to the GetCharBmpOffset function lines 26 27 2 Using that rectangle we copy the bits from our memory bitmap to the display using the BitBlt API lines 28 30 3 The rest of the lines in the loop updates the position of the destination and take care of advancing to the next line 4 Lines 44 48 concern the cleanup We tell windows that we are finished with drawing using the EndPaint API line 44 We deselect our bitmap from the memory device context line 45 then we delete the memory DC Note that we must do things in that order since a bitmap can t be deleted if it is selected in a DC Then we delete the background brush we created 308 C
516. s that as long as the Next pointer is not NULL we position our roving pointer hence the name rvp to the next element and repeat the test We suppose obviously that the last element of the list contains a NULL Next pointer We ensure that this condition is met by initializing the rvp gt Next field to NULL when we initialize the new element To access a list of n elements we need in average to access n 2 elements Other functions are surely necessary Let s see how a function that returns the nth member of a list would look like LIST ListNth LIST list int n while list amp amp n gt 0 list list gt Next return list Note that this function finds the nth element beginning with the given element which may or may not be equal to the root of the list If there isn t any nth element this function returns NULL If this function is given a negative n it will return the same element that was passed to it Given a NULL list pointer it will return NULL Other functions are necessary Let s look at Insert LIST Insert LIST list LIST element LIST tmp if list NULL return NULL if list element return list tmp list gt Next list gt Next element if element element gt Next tmp return list We test for different error conditions The first and most obvious is that list is NULL We just return NULL If we are asked to insert the same element to
517. sabling tooltips Although ToolTips may be helpful you might find it annoy ing To disable it go to HKEY_USERS DEFAULT Control Panel Desktop On the right pane double click UserPrefer encemask and change the value to 3E 00 00 00 To enable it again change the value back to BE 00 00 00 a Windows registry guide http www winguides com registry where I took some of the examples above They distribute for free a very interesting guide in windows help format full of tips like that Another similar site is http www activewin com tips reg index shtml 2 17 Etc At last count there was around 17000 APIs in the file Icc lib apilist txt This file is used by the linker to figure out in which library a given API is found You can look at it to get an impression of the richness of the windows API There are functions for many kinds of stuff and here I will just try to give a very superficial overview of all that You are invited to down Etc 313 load the SDK documentation for free from the Microsoft MSDN site Lcc win gives you access to all this Clipboard Just that A common repository for shared data Quite a few formats are available for images sound text etc Communications Read and write from COM ports Consoles and text mode support The msdos window improved libraries DLLs Debug Help Why not Write a debugger Any one can do it It is quite interesting as a progra
518. scanning function each time a file is found We define typedef int callback char This means a function pointer called callback that points to a function that returns an int and receives a char as its argument This function pointer will be passed to our scanning func tion and will return non zero scanning should be continued or zero scanning should stop Here is a possible implementation of this concept include lt stdio h gt include lt windows h gt include lt direct h gt Here is our callback definition typedef int callback char This function has two phases In the first we scan for normal files and ignore any directories that we find For each file that matches we call the given function pointer The input the char spec argument should be a character string like c or h If several specifications are needed they should be separated by the semi colon char For instance we can use c h asm to find all files that match any of those file types The second argument should be a function that will be called at each file found int ScanFiles char spec callback fn char p q Used to parse the specs char dir MAX PATH Contains the starting directory char fullname MAX _PATH will be passed to the function HANDLE hdir HANDLE h WIN32_FIND_DATA dirdata WIN32_FIND_DATA data Get the current directory so that we can always
519. second parameter is actu ally a char pointer In the days of Windows 2 0 however in the cramped space of MSDOS with its 640K memory limit passing a real character string was out of the question and it was decided to save space that instead of passing the name of the dialog box resource as a real name it should be passed as a small integer in a pointer The pointer should be a 32 bit pointer with its upper 16 bits set to zero and its lower 16 bits indicating a small constant that would be searched in the resource data area as the name of the dialog box template to load Because we need to load a template i e a series of instructions to a built in interpreter that will create all the necessary small windows that make our dialog box As you have seen dia log boxes can be quite complicated full of edit windows to enter data buttons trees what have you It would be incredible tedious to write all the dozens of calls to the CreateWin dow API passing it all the coords of the windows to create the styles etc 103 When the IDE asks you if you want to open it as a resource say NO We want to look at the text of that file this time Introduction to windows programming 233 To spare you this Herculean task the designers of the windows system decided that a small language should be developed together with a compiler that takes statements in that language and produce a binary file called resource file This resource files are boun
520. sed without prototypes I have thought many times to introduce that into Icc win because ignoring the function prototype is always an error But for compatibility reasons I haven t done it yet 1 7 3 Function definitions Function definitions look very similar to function declarations with the difference that instead of just a semi colon we have a block of statements enclosed in curly braces as we saw in the function main above Another difference is that here we have to specify the name of each argument given these identifiers aren t optional any more they are needed to be able to refer to them within the body of the function Here is a rather trivial example int addOne int input return input 1 1 7 4 Scope of identifiers The scope of an identifier is the extent of the program where the identifier is active i e where in the program you can use it There are three kinds of identifier scopes 1 File scope An identifier with file scope can be used anywhere from the its definition till the end of the file where it is declared 2 Block scope The identifier is visible within a block of code enclosed in curly braces and Y 3 Function prototype scope This scope is concerned with the identifiers that are used within function prototypes For instance void myFunction int argl the identifier argl is within prototype scope and disappears immediately after the prototype is parsed We could
521. sed is the given precision The argument is a pointer and is printed in pointer format Under Icc win this is the same as the unsigned format u The argument is a pointer to int default pointer to short h modifier or pointer to long long 11 modifier Contrary to all other conversions this conversion writes the number of characters written so far in the address pointed by its argu ment e E Signed decimal floating point conversion Argument is of type double default or long double withthe L modifier or gf loat with the q modifier The result will be displayed in scientific notation with a floating point part the letter e for the e format or the letter E for the E format then the exponent If the precision is zero no digits appear after the decimal point and no point is shown If the flag is given the point will be printed Signed decimal floating point conversion Argument is of type double default or long double with the L modifier If the argument is the special value infinite inf will be printed If the argument is the special value NAN the letters nan are written g G This is the same as the above but with a more compact representation Argu ments should be floating point Trailing zeroes after the decimal point are removed and if the number is an integer the point disappears If the flag is present this stripping of zeroes is not performed The scientific notation as in f
522. server must then listen on that IP address and port for incoming connection requests To listen on a socket call the listen function passing the created socket and the maximum number of allowed connections to accept as parameters printf Error listening on socket n if listen Socket 1 SOCKET_ERROR 3 7 2 3 Accepting connections Once the socket is listening for a connection we must handle connection requests on that socket To accept a connection on a socket we create a temporary socket object for accepting connections SOCKET AcceptSocket Create a continuous loop that checks for connections requests If a connection request occurs call the accept function to handle the request printf Waiting for a client to connect n 402 C Tutorial while 1 AcceptSocket SOCKET_ERROR while AcceptSocket SOCKET_ERROR AcceptSocket accept Socket NULL NULL When the client connection has been accepted assign the temporary socket to the original socket and stop checking for new connections printf Client Connected n Socket AcceptSocket break There we go we have a socket ready to send and receive data 3 7 3 Client side For a client to communicate on a network it must connect to a server To connect to a socket we create a sockaddr_in object and set its values sockaddr_in clientService clientService sin_family AF_INET
523. sesossesossescoosssossocsesesocossososssosossoosesossosesessesessessses marker 2 15 Building custom controls In many cases it is a good idea to develop a class of windows that can be used in several appli cations with the same interface The idea is to encapsulate into a dll module or just in a static library a specialized window that will do one kind of thing a grid for a database application or for using a simpler example an lcd simulation display The objective is to build a simple display window that simulates a small lcd display that shows a few lines of text To build this application we follow the usual procedure we generate an application with the wizard and we change the display of the window instead of drawing a blank window we add a handler for the WM_PAINT message like this LRESULT CALLBACK MainWndProc HWND hwnd UINT msg WPARAM wParam LPARAM lParam switch msg case WM_PAINT DoPaint hwnd break case WM_DESTROY return 0 In our DoPaint procedure we will do just that paint the lcd window We need first to draw a simple character set from which we will copy the characters into the display Here is a simple one In this bitmap we use three colors a light blue for drawing the body of the characters a darker blue for drawing the background of the characters and black to draw the space 306 C Tutorial between each character 4 Our drawing procedure DoPa
524. sional array using the indexes il i2 in See Arrays on page 51 Table 34 23 This access the 35 line 24 P position of Table fn args Call the function fn and pass it the comma separated argument list args see Function call syntax on page 54 printf za 5 An overview of the whole language 41 fn arg See Functions with variable number of arguments on page 54 fn args Call the function whose machine address is in the pointer fn struct field Access the member of the structure Customer Name struct gt field Access the member of the structure through a pointer Customer gt Name Assign to the variable the value of the right hand var value side of the equals sign See Assignment on a 45 page 55 Equivalent to expression expression 1 expressiont Increment expression after using its value a i See Postfix on page 57 Equivalent to expression expression 1 expression Decrement expression after using its value a i see Postfix on page 57 Equivalent to expression expression 1 Increment texpression eai a AFI expression before using its value i eanna Equivalent to Expression expression 1 7 SrTex als Sd p Decrement expression before using it Return the machine address of object The type of amp object 5
525. sition WM_WINDOWPOSCHANGED Sent to a window whose size position or place in the Z order has changed as a result of a call to the SetWin dowPos function or another window management function WM_WINDOWPOSCHANGING Same as above message but sent before the changes WM_GETMINMAXINFO Sent to a window when the size or position of the win dow is about to change You can use this message to override the window s default maximized size and position or its default minimum or maximum tracking size WM_ENTERSIZEMOVE Sent one time to a window after it enters the moving or sizing modal loop The window enters the moving or sizing modal loop when the user clicks the window s title bar or sizing border or when the window passes the WM_SYSCOMMAND message to the DefWin dowProc function and the wParam parameter of the message specifies the SC_MOVE or SC_SIZE value The operation is complete when DefWindowProc returns WM_EFXITSIZEMOVE Sent one time to a window after it has exited the mov ing or sizing modal loop 2 9 Window controls A control is a technical name for a child window that has a characteristic appearence and fills a functionality for user input A list box for instance is a child window that has a rectangu lar appearence with lines and scrollbars that displays a list of items When the system creates a dialog box it creates all its child windows ac
526. sizeof szHost sizeof szHost 0 Set non zero lengths to obtain pointer to the URL Path note if we threat this pointer as a NULL terminated string this pointer will contain Extra Info as well urlComp dwUrlPathLength 1 Crack HTTP scheme urlComp dwSchemeLength 1 Parsing an URL is a tricky business that we better leave for an API than trying to do this our selves if WinHttpCrackUrl szWURL 0 0 amp urlComp goto cleanup Note that all errors are processed using a goto cleanup what simplifies the error handling The famous goto statement is not that bad after all This is it We attempt to open a connection now Open an HTTP session The HTTP Protocol 391 rceContext hConnect WinHttpConnect hSession szHost urlComp nPort 0 if NULL rcContext hConnect goto cleanup Note that no actual connection will be done until we start a request This is a GET request dwOpenRequestFlag INTERNET_SCHEME HTTPS urlComp nScheme WINHTTP_FLAG SECURE 0 Open a GET request rcContext hRequest WinHttpOpenRequest rcContext hConnect L GET urlComp lpszUrlPath NULL WINHTTP_NO_REFERER WINHTTP_DEFAULT_ACCEPT_TYPES dwOpenRequestFlag if rcContext hRequest 0 goto cleanup Now we are ready to send our request This will open a connection Se
527. some action indicated by the menultem code break This code begins with a cast of the Param message parameter into a pointer to a NMHDR structure Then it examines the passed notification code If it is a right click it fills a TV_HITTESTINFO structure with the coordinates of the mouse and translates those into the coordinates of the tree control that this code supposes in a global variable hwndTree The control should return either NULL meaning there is no item at that position or the handle of an item that was right clicked with the mouse If there was an item a context menu is created shown and the result is an integer indicating which menu item was chosen if any This is one of the many ways you can interact with the window system Each control will have its own interface since they are all different and perform quite different actions You can see the above code in action when you click with the right button in an item of the project workspace window in Wedit You use the CreateWindow API with a predefined window class You pass it as the parent window parameter the handle of the window where you want to put the control on For instance if you want to create somewhere in your window an edit field you would write hEditWnd CreateWindow EDIT window class is edit NULL WS_CHILD WS_VISIBLE ES_MULTILINE S_VSCROLL WS_HSCROLL ES_AUTOHSCROLL ES_AUTOVSCROLL
528. sorry for the inconvenience 3 Hello aaaa 4 Hello aaaaa 5 Hello aaaaaa 6 Hello aaaaaaa 7 Hello aaaaaaaa 8 Hello aaaaaaaaa 9 Hello aaaaaaaaaa Hello aaaaaaaaaaa Yes we are sorry for the inconvenience And no it doesn t help to call Microsoft It is not their fault this time What happened Obvious The printf specification 10s will NOT limit the copy to 10 characters It just says that the string will be padded at the left with blanks if it is shorter than 10 chars If not sprintf will continue to copy the characters without any limit Our function can be made safe very easily by just using snprintf instead of its dangerous cousin sprintf The snprintf function will take an optional integer argument after the for mat string telling it how many characters it should write at most into its destination buffer void func char p char buf 10 1 memset buf 0 sizeof buf limit string to 10 chars by using snprintf snprintf buf 10 10s p printf Hello s n buf This time we see the expected output 0 Hello a 1 Hello aa 2 Hello aaa 3 Hello aaaa 4 Hello aaaaa 5 Hello aaaaaa 6 Hello aaaaaaa 7 Hello aaaaaaaa 8 Hello aaaaaaaaa 9 Hello aaaaaaaaaa 10 Hello aaaaaaaaaa 11 Hello aaaaaaaaaa 12 Hello aaaaaaaaaa Programming with security in mind 215 1 2 3 Do not assume correct input Do you remembe
529. ss the OK button and we do what we did with the dialog in the DLL our first example The finished dialog should look roughly like this Text Search An edit field and two push button for OK and Cancel The edit field should receive the ID IDTEXT Now comes the interesting part How to connect all this We have to first handle the WM_COMMAND message so that our main window handles the menu message when this menu item is pressed We go to our window procedure MainWnd Proc Here it is 290 C Tutorial LRESULT CALLBACK MainWndProc HWND hwnd UINT msg WPARAM wParam LPARAM lParam switch msg case WM_SIZE SendMessage hWndStatusbar msg wParam lParam InitializeStatusBar hWndStatusbar 1 break case WM_MENUSELECT return MsgMenuSelect hwnd msg wParam lParam case WM_COMMAND HANDLE WM COMMAND hwnd wParam 1Param MainWndProc_OnCommand break case WM_DESTROY PostQuitMessage 0 break default return DefWindowProc hwnd msg wParam lParam return 0 We can see that it handles already quite a few messages In order We see that when the main window is resized it resizes its status bar automatically When the user is going through the items of our menu this window receives the WM_MENUSELECT message from the system We show the appropriate text with the explana tions of the actions the menu item in the status bar When a command from the menu or from a chil
530. ssages we just use our friend GetDlgItemText to get the length of the text in the edit field If there is some text we enable the IDOK button with the API EnableWindow If there is NO text we disable the IDOK button with the same API Since 109 I remember calling the software support when installing some hardware many of the options of the installation software were disabled but there was no way of knowing why 242 C Tutorial we are getting those notifications each time the user types a character the reaction of our IDOK button will be immediate But we have still one more thing to do before we get this working We have to modify our Ini tializeApp procedure to start the dialog box with IDOK disabled since at the start there is no text in the entry field static int InitializeApp HWND hDlg WPARAM wParam LPARAM lParam SetFocus GetDlgItem hDlg IDENTRYFIELD Disable the IDOK button at the start EnableWindow GetDlgItem hDlg IDOK 0 return 1 We recompile and it works The OK button starts disabled grayed and when we type the first character it becomes active just as we wanted When we select all the text in the entry field and then erase it we observe that the button reverts to the inactive state 2 2 User interface considerations There was another way of informing the user that text must be entered a MessageBox call telling him her precisely what is wrong This alternative making s
531. ssible 1 3 10 Careful with unsigned numbers Consider this loop int i for i 5 i gt 0 i printf i Sd n i This will terminate after 6 iterations This loop however will never terminate unsigned int i for i 5 i gt 0 i printf i Sd n i The loop variable i will decrease to zero but then the decrement operation will produce the unsigned number 4294967296 that is bigger than zero The loop goes on forever Note too that the common windows type DWORD is unsigned 1 3 11 Changing constant strings Constant strings are the literal strings that you write in your program For instance you write outScreen Please enter your name This constant string Please enter your name is stored under Icc win in the data section of your program and can be theoretically modified For instance suppose that the routine out Screen adds a r n to its input argument This will be in almost all cases a serious problem since 1 The compiler stores identical strings into the same place For instance if you write a This is a string b This is a string there will be only one string in the program The compiler will store them under the same address and if you modify one the others will be automatically modified too since they are all the same string 2 If you add characters to the string with strcat for instance you will destroy the other strings or other data that lies
532. stance c 2 The second is to apply a regular expression to each line of the set of files A regular expression is a program that will be interpreted by a special interpreter at run time We have first to compile it then we apply it to each line Here is then a first approximation of grep 91 http en wikipedia org wiki Regular_expression 210 C programming with Icc win32 include include include include include include include int main lt stdio h gt lt regexp h gt lt io h gt lt stdlib h gt lt string h gt lt direct h gt lt shlwapi h gt int argc char argv regexp expression struct _finddata_t fd long h int matches char p unsigned char path MAX_PATH 2 unsigned char currentdir MAX PATH unsigned char Path 2 MAX PATH if arge lt 3 1 fprintf stderr Usage grep lt expression gt lt files gt n return 1 expression regcomp argv 1 2 if expression NULL fprintf stderr Incorrect reg expression s n argv 1 return 1 if argv 2 0 amp amp argv 2 1 3 getcwd currentdir sizeof currentdir 1 strcpy path currentdir strcat path strcat path argv 2 p strrchr path if p p 0 PathCanonicalize Path path p strrchr argv 2 if p NULL strcat Path p argv 2 strcat Path p else strcpy Path a
533. ster it will return to the value 1 even if we incremented it before calling longjmp The only way to avoid this problem is to force the compiler to allocate local Variable in mem ory using the volatile keyword The declaration should look like this int volatile localVariable This instructs the compiler to avoid any optimizations with this variable i e it forces allocat ing in the stack and not in a register This is required by the ANSI C standard You can t assume that local variables behave normally when using longjmp setjmp 88 C programming with Icc win32 The setjmp longjmp functions have been used to implement larger exception handling frame works For an example of such a usage see for example Exceptions and assertions in C Interfaces and implementations of David Hanson Chapter 4 Simple programs 89 1 17 Simple programs To give you a more concrete example of how C works here are a few examples of very simple programs The idea is to find a self contained solution for a problem that is simple to state and understand 1 17 1 strchr Find the first occurrence of a given character in a character string Return a pointer to the char acter if found NULL otherwise This problem is solved in the standard library by the st rchr function Let s write it The algorithm is very simple We examine each character If it is zero this is the end of the string we are done and we return NULL to indicate that
534. storage to the function where the function writes its result This is done automati cally and does not need any special intervention from the user Other compilers may have different schematas for returning a structure Under Windows lcc win uses the guidelines proposed by Microsoft Non Microsoft compilers under windows may use different schematas 1 13 20 3 Never return a pointer to a local variable Suppose a function like this double fn void double m 42 This exception is a misguided attempt of the C standards committee to copy the C behavior 62 C programming with Icc win32 i ee return amp m This is a serious error that will be flagged by the lcc win compiler but other compilers may be less explicit The problem here is that the variable m lives in the activation record of the pro cedure fn Once the procedure returns all storage associated with it is freed including all storage where local variables are stored The net effect of this return is to return a bad address to the calling function The address is bad since the storage is no longer valid Any access to it can provoke a trap or worst can give wrong values when accessed 1 13 21 Unsigned Integer types long long long int short and char have the most significant bit reserved for the sign bit This declaration tells the compiler to ignore the sign bit and use the values from zero the 2 for the values of that type For instance
535. szClassName dialog RegisterClass amp wc You see that the code is the same as the code we had originally in WinMain then in our Get String procedure etc To finish LibMain we handle the message DLL_PROCESS_DETACH unregistering the class we registered before With this our GetString procedure is simplified We do not need to test our flag to see if the class has been registered any more We can be certain that it was int APIENTRY __declspec dllexport GetString char prompt char destbuffer int bufferlen int result result DialogBoxParam hinst MAKEINTRESOURCE IDD_MAINDIALOG NULL DLGPROC DialogFunc int prompt if result 1 strncpy destbuffer buffer bufferlen 1 destbuffer bufferlen 1 0 return result We compile and link our DLL by pressing F9 Note that when we are building a DLL Icc win will generate three files and not only one as with a normal executable 1 We obtain of course a dialog dll file that contains the DLL 2 We obtain an import library that allows other programs to be linked with this DLL The name will be dialog lib but this is not a normal library It is just a library with almost no code containing stubs that indicate the program loader that a specific DLL is used by the program 3 We obtain a text file called dialog exp that contains in text form the names that are exported from the DLL If for any reason we
536. t if Frequencies count 0 printf 3c 4d d n count count Frequencies count return 0 We compile link and then we write frequencies frequencies c 957 chars in file Using arrays and sorting 105 Well sorting definitely works you read this display line by line but we note with dismay that A 192 1 A 193 1 A 194 1 A 195 1 A 196 1 A 197 1 198 1 199 1 200 1 201 1 202 1 203 2 Tot 204 iS 2 205 S22 I 206 2 I 207 2 208 2 209 3 210 3 O 211 3 Op 272 TS O 82 e EB SC 214y 3 x 215 4 216 4 Ue C212 4 218 4 219 5 U 220 5 Y 221 5 B 222 5 BR 223 6 224 6 225 6 226 79 A 227 7 A 228 7 A 229 7 230 7 q 231 7 232 8 233 8 234 10 E 235 10 i 236 10 tC 23S 17 fA 238 et 239 13 240 16 fi 241 20 242 21 OF 243 S21 6 244 21 6 245 24 246 24 247 25 248 28 249 35 250 38 251 39 252 46 253 52 bp 254 52 y 255 93 All the character names are wrong Why Well we have never explicitly stored the name of a character in our integer array it was implicitly stored The sequence
537. t lt drive gt n printf For example nmount c mnt cdrom g n return 1 Js We should do some error checking on the inputs Make sure there are colons and backslashes in the right places etc bFlag GetVolumeNameForVolumeMountPoint argv 2 input volume mount point or directory Buf output volume name buffer BUFSIZE size of volume name buffer i if bFlag TRUE printf Retrieving volume name for s failed n argv 2 return 2 Check that the file system supports mounting bFlag GetVolumeInformation argv 2 bufl BUFSIZI NULL amp nl amp flags fsname 256 Gl if 0 flags amp FILE_SUPPORTS_REPARSE_POINTS printf File system doesn t support mount points n return 3 printf Volume name of s is s n argv 2 Buf if strlen argv 1 lt 2 printf Incorrect path name s n argv 1 return 4 strncpy fsname argv 1 sizeof fsname 1 fsname sizeof fsname 1 0 FAQ 351 Add a trailing backslash if not this call will not work if fsname strlen fsname 1 strcat fsname bFlag SetVolumeMountPoint fsname mount point Buf volume to be mounted if bFlag printf Attempt to mount s at s failed Error code d n argv 2 argv 1 GetLastError else printf s mounted in s n argv 2 argv 1 return bFlag 2 21 27 2 Umount Once we have mount
538. t Word pw2 gt Word return pwl gt Count pw2 gt Count Note that we have implemented secondary sort key If the counts are the same we sort by alphabetical order within a same count void DoReports char filename int i int idx 0 Index into the resulting table Print file name and number of words printf s d different words n filename words allocate the word list pointer table WORDLIST tab more_memory words sizeof WORDLIST Go through the entire hash table for i 0 i lt sizeof WordTable sizeof WordTable 0 i WORDLIST wl WordTable i while wl look at the list at this slot tab idx wl wl wl gt Next idx if idx gt words amp amp wl fprintf stderr program error n exit EXIT_FAILURE Sort the table qsort tab words sizeof WORDLIST comparewords Print the results for i 0 i lt words itt printf s 5d n tab i gt Word tab i gt Count We start by printing the name of the file and the number of different words found Then we go through our hash table adding a pointer to the word list structure at each non empty slot Note that we test for overflow of the allocated table Since we increment the counter each time that we add a word it would be very surprising that the count didn t match with the number of items in the table But it is better to verify this After filling our table for th
539. t all in those systems the main function will be defined as always int main void 21 The detailed description of what happens when we start a program what happens when we compile how the compiler works etc are in the technical documentation of Icc win With newer versions you can use the compilation driver Ic exe that will call the linker automatically Iteration constructs 13 1 5 Iteration constructs We introduced informally the for construct above but a more general introduction to loops is necessary to understand the code that will follow There are three iteration constructs in C for do and while 1 5 1 for The for construct has 1 An initialization part i e code that will be always executed before the loop begins 2 A test part i e code that will be executed at the start of each iteration to determine if the loop has reached the end or not and 3 An increment part i e code that will be executed at the end of each iteration Normally the loop counters are incremented or decremented here The general form is then for init test increment statement block Within a for statement you can declare variables local to the for loop The scope of these variables is finished when the for statement ends include lt stdio h gt int main void for int i 0 i lt 2 i printf outer i is d n i for int i 0 1 lt 2 it printf
540. t for the xy FAQ 353 modeless dialog box hwnd aA if thwnd IsDialogMessage hwnd amp msg TranslateMessage amp msqg DispatchMessage amp msqg The following describes how to incorporate the progress dialog as part of an application s sub task that is CPU intensive The PROGRESS_DLG resource should contain a button with an ID of 2 because this is the wParam of the WM COMMAND that will be sent when the user presses the ESC key The button should also have the BS_DEFPUSHBUTTON style so that the ENTER key will also result in the termination of the CPU intensive subtask FARPROC lpProgressProc HWND hwndProgress This needs to be global if accessed by other modules Initialize before starting CPU intensive work x lpProgressProc MakeProcInstance ProgressDlgProc hInst Current instance hwndProgress CreateDialog hInst Current instance PROGRESS_DLG Resource hwndParent Parent handle xy lpProgressProc Instance address ShowWindow hwndProgress Start CPU intensive work here Before or after each unit of work the application should do the following ProgressYield hwndProgress if Cancel TRUE break Terminate CPU intensive work immediately End CPU intensive work here DestroyWindow hwndProgress FreeProcInstance lpProgressProc 2 22 2 How do I show in
541. t in detail We include the standard header string h to get the definitions of string handling functions like stricmp We define our comparison function with int compare const void argl const void arg2 This means that our compare function will return an int and that takes two arguments named arg1 and arg2 that are pointers to any object void The objects pointed to by arg1 and arg2 will not be changed within this function i e they are const We need to get rid of the void within our compare function We know we are going to pass to this function actually pointers to characters i e machine addresses to the start of character strings so we have to transform the arguments into a type we can work with For doing this we use a cast A cast is a transformation of one type to another type at compile time Its syntax is like this newtype expression In this example we cast a void to a char a pointer to a pointer of characters The whole expression needs quite a lot of reflection to be analyzed fully Return here after reading the section about pointers Note that our array argv can be used as a pointer and incremented to skip over the first ele ment This is one of the great weaknesses of the array concept of the C language Actually 60 Most compilers do not have the C99 standard implemented In those compilers you can t do this and you will have to declare the loop counter as a normal local va
542. t side 402 Sending and receiving data 402 Simplifying sockets programming with Icc win 402 Why learn C 1 Introduction to C This tutorial to the C language supposes you have the lcc win compiler system installed You will need a compiler anyway and Icc win is free for you to use so please if you haven t done that yet download it and install it before continuing http www g software solutions com What the C language concerns this is not a full fledged introduction to all of C There are other better books that do that see the bibliography at the end of this book Even if I try to explain things from ground up there isn t here a description of all the features of the language Note too that this is not just documentation or a reference manual Functions in the standard library are explained of course but no exhaustive documentation of any of them is provided in this tutorial But before we start just a quick answer to the question 1 1 Why learn C C has been widely criticized and many people are quick to show its problems and drawbacks But as languages come and go C stands untouched The code of Icc win has software that was written many years ago by many people among others by Dennis Ritchie the creator of the language itself The answer to this question is very simple if you write software that is going to stay for some time do not learn the language of the day learn C C doesn t impose you any p
543. t we would lose the possibility of knowing exactly which operation failed This is in many cases not very important we could very well be interested that somewhere there was a serious error without bothering to investigate which operation was that it failed 1 1 2 Reinitializing the floating point environment Things can become messy and you would like to reset everything to a known state The stan dard provides the macro FE_DFL_ENV that represents the address of the default environ ment the one you started with In lIcc win this environment is stored in the __default_fe_env global variable so this macro is just define FE_DFL_ ENV amp _default_fe_ env You can reset everything to its default state with fesetenv FE_DFL_ENV The default environment in Icc win has the following characteristics 1 The rounding mode is set to round to nearest 2 The precision of the FPU is set to full precision 80 bits 3 All exceptions are masked i e the result of invalid operations is a NAN not a trap 1 1 3 Numerical stability Suppose we have a starting point and a recurrence relation for calculating the numerical value of an integral The starting value is given by To in x 5 4 1n 6 In 5 0 182322 90 I have this example from the very good book Numerical Mathematics and Scientific Computation by Germund Dahlquist and Ake Bj rck Available on line at http www mai liu se akbjo NMbook html Using the floating
544. t with the binary and operation The number one has only one bit set the rightmost one By the way one is a power of two Note that the return expression could have also been written like this return bitcount 1 The intention of the program is clearer with the if expression How can this program fail The while loop has only one condition that n is different than zero i e that n has some bits set Since we are shifting out the bits and shifting in always zero bits since bit count is unsigned in a 32 bit machine like a PC this program will stop after at most 32 iterations Running mentally some cases a good exercise we see that for an input of zero we will never enter the loop bit count will be zero and we will return 0 the correct answer For an input of 1 we will make only one iteration of the loop Since 1 amp lis 1 bitcount will be incremented and the test will make the routine return 1 the correct answer If n is three we make two passes and bitcount will be two This will be different than 1 and we return zero the correct answer Anh Vu Tran anhvu tran ifrance com made me discover an important bug If you change the declaration of n from unsigned int to int without qualification the above function will enter an infinite loop if n is negative Why When shifting signed numbers sign is preserved so the sign bit will be carried through pro voking that n will become eventually a string of 1 bits nev
545. t you know what is going on however But now we can see how we can make Wedit generate the code for us The code generator is not enabled by default You have to do it by choosing the Output item in the resources menu This leads to an impressing looking box like this Cancel Definitions and prototypes h Help h winexample winexampleres h IV Generate Binary resources res h winexample winexample res IV Generate RC ASCII resource file 1c h winexample winexample rc M Generate Dialogs only ascii resource file dlg I Generate Generate m User callbacks file fr winexample winexample_cbk c Additional include files Dictionary for automatic language translation Include path for bitmaps and other baggage files fr lec include This dialog shows you the files that will be generated or used by Wedit Those that will be generated have a box at the right to enable or disable their generation The others are used if available but only for reading The last item is an additional path to look for bitmaps icons and other stuff that goes into resources You notice that the first item is disabled You enable it and type the full path of a file where you want Wedit to write the dialog procedures Notice that by default the name of this file is lt name of the project gt c This could provoke that your winexample c that we worked so hard to write could be overw
546. ta Opera tions are allowed between compatible types and not between any data whatsoever It is possi ble to add two integers or an integer and a floating point number and even an integer and a complex number It is not possible to add an integer to a function or to a character string the operation has no meaning for those types An operation implies always compatible types between the operands In C all data must be associated with a specific type before it can be used All variables must be declared to be of a known type before any operation with them is attempted since to be able to generate code the compiler must know the type of each operand C allows the programmer to define new types based on the previously defined ones This means that the type system in C is static i e known at compile time but extensible since you can add new types This is in contrast to dynamic typing where no declarations are needed since the language associates types and data during the run time Dynamic typing is much more flexible but this flexibility has a price the run time system must constantly check the types of the operands for each operation to see if they are compatible This run time checking slows down the program considerably In C there is absolutely no run time checking in most operations since the compiler is able to check everything during the compilation which accelerates the execution of the program and allows the compiler to discove
547. tack contents will change 2 21 5 Disabling the screen saver from a program Under Windows NT you can disable the screen saver from your application code To detect if the screen saver is enabled use this SystemParametersInfo SPI_GETSCREENSAVEACTIVE 0 pvParam 0 i On return the parameter pvParam will point to TRUE if the screen saver setting is enabled in the system control panel applet and FALSE if the screen saver setting is not enabled Some Coding Tips 337 To disable the screen saver setting call SystemParametersInfo with this SystemParametersInfo SPI_SETSCREENSAVEACTIVE FALSE 0 SPIF_SENDWININICHANGE 2 21 6 Drawing a gradient background You can draw a smooth gradient background using the following code void DrawBackgroundPattern HWND hWnd HDC hDC GetDC hWnd Get the DC for the window RECT rectFill Rectangle for filling band RECT rectClient Rectangle for entire client area float fStep How large is each band HBRUSH hBrush int iOnBand Loop index How large is the area you need to fill GetClientRect hWnd amp rectClient Determine how large each band should be in order to cover the client with 256 bands one for every color intensity level fStep float rectClient bottom 256 0f Start filling bands for iOnBand 0 iOnBand lt 256 iOnBand Set the location of the curr
548. tandard should present code that is 100 right There are so few lines of code in the standard that making those lines buffer overflow free is not a daunting task by any means 1 28 1 3 The attitude of the committee I am not the first one to point out this problem In a Defect Report filed in 2001 Clive Feather proposed to fix it The answer of the committee was that if any of the members of the input argument was out of range this was undefined behavior and anything was permitted including corrupting memory Corrupting memory provokes bugs almost impossible to trace The symptoms vary and the bug can appear and disappear almost at random depending on the linker and what data was exactly beyond the overflowed buffer This means that the asctime function can t be relied upon Any small mistake like passing it an uninitialized variable will provoke no immediate crash but a crash later in some completely unrelated program point 140 C programming with Icc win32 72 Defect Report 217 Submitter Clive Feather UK Submission Date 2000 04 04 Reference Document N A Version 1 3 Date 2001 09 18 15 51 36 Subject asctime limits Summary The definition of the asctime function involves a sprintf call writing into a buffer of size 26 This call will have undefined behavior if the year being represented falls outside the range 999 9999 Since appli cations may have relied on the size of 26 this should not be
549. tdio h gt include lt seh h gt int main void char p NULL __try p 0 _ except EXCEPTION_EXECUTE_HANDLER printf Ooops there was a problem with this program n printf Please call the maintenance team at 0 800 XxXX n return 0 This will print D lec mce38 test gt test Ooops there was a problem with this program Please call the maintenance team at 0 800 XXxX If we change it to include lt stdio h gt include lt seh h gt int main void char p 10 try p 0 82 This is an extension of Microsoft and is not part of the standard language It is supported by many compilers under windows but not by all of them Advanced C programming with Icc win 183 printf No exceptions n _ except EXCEPTION_EXECUTE_HANDLER printf Ooops there was a problem with this program n printf Please call the maintenance team at 0 800 XxXX n return 0 This will now print No exceptions We have three parts here The first one is the protected code block enclosed by __try This block can contain code that provokes exceptions To leave it prematurely you use the __leave expression The second part is an integer expression that appears between parentheses after the __ except keyword This expression should eventually evaluate to one of the three constants defined in the lt seh h gt header file EXCEPTION_EXECUTE_HANDLER 1 means that the code in th
550. te that this shouldn t be a define but actually a calculated variable Windows allows us to query the horizontal and vertical screen dimensions but for a simple drawing of a spiral a define will do The function PlotPixelAt looks like this void PlotDotAt HDC hdc double x double y COLORREF rgb SetPixel hdc int x int y rgb The first argument is an HDC an opaque pointer that points to a device context not fur ther described in the windows documentation We will speak about opaque data structures later A COLORREF is a triple of red green and blue values between zero black and 255 white that describe the colors of the point We use a simple schema for debugging purposes we paint the first arm black 0 0 0 and the second red 255 0 0 In event oriented programming the question is which event will provoke the execution of this code Windows sends the message WM_PAINT to a window when it needs repainting either because its has been created and it is blank or it has been resized or when another window moved and uncovered a portion of the window We go to out MainWndProc function and add code to handle the message We add case WM_PAINT dopaint hwnd break We handle the paint message in its own function This avoids an excessive growth of the MainWndProc function Here it is void dopaint HWND hwnd PAINTSTRUCT ps HDC hDC hDC BeginPaint hwnd amp ps DrawGalaxy
551. ted from an excellent article by Jon Pincus published in MSDN June 2000 138 Simply looking at this name ERROR_SUCCESS implies that there is a big problem with the peo ple that designed that stuff It is an error code or a success indication 332 C Tutorial mean an error code Note that the value of zero that in the boolean convention above indicates failure means the contrary here 3 Returning a NULL pointer This failure indication is used in the standard C library malloc realloc and many others return NULL for failure As with the boolean convention some other means are necessary to distinguish the different kinds of failures 4 Returning an impossible value Sometimes this value is zero for instance in the API GetWindowsDirectory sometimes is 1 for instance the fgets function in the C library or many other values This convention becomes very difficult to follow and memorize when applied to a large API like the windows API 5 Throwing a C exception This is very nice in C but it will never work with C or with COM It is illegal to throw a C exception in COM Besides the runtimes of different compilers handle C exceptions in a different way so they are incompatible with each other Anyway if you work with Icc win you will be spared this 6 Using the RaiseException API This is the normal way of using structured exception handling in Icc win It has its drawbacks too since it doesn t fit very well with CO
552. tem for instance or when you need to allow the user to change the current directory of your application The windows shell offers a ready made set of functions for you and the resulting function is quite short Let s first see its specification i e what do we want as an interface to this function Required is a character string where the result will be written to and a title for the user inter face element The result should be 1 if the path contains a valid directory O if there was any error the user cancelled whatever To be clear about the specifications let s look at this example int main void char path MAX_PATH if BrowseDir Choose a directory path printf You have choosen s n path else printf action cancelled n return 0 How do we write BrowseDir in windows Here it is include lt shlobj h gt include lt stdio h gt int BrowseDir unsigned char Title char result PMALLOC pMalloc 1 BROWSEINFO browselInfo 2 PITEMIDLIST ItemIDList 3 326 C Tutorial INE E O 4 if S_OK SHGetMalloc amp pMalloc 5 return 0 memset amp browselInfo 0 sizeof BROWSEINFO 6 browseInfo hwndOwner GetActiveWindow 7 browseInfo pszDisplayName result 8 browseInfo lpszTitle Title 9 browseInfo ulFlags BIF_NEWDIALOGSTYLE 10 ItemIDList SHBrowseForFolder amp browselInfo 11 if ItemIDList NULL result 0 if SHGetP
553. tents Initialize the print job if StartDoc hdcPrinter amp di gt 0 Prepare to send a page if StartPage hdcPrinter gt 0 340 C Tutorial Retrieve the information describing the surface GetObject hbm sizeof DIBSECTION amp ds Print the contents of the surface StretchDIBits hdcPrinter 0 O iWidth iHeight 0 O re right re bottom ds dsBm bmBits LPBITMAPINFO amp ds dsBmih DIB RGB COLORS SRCCOPY Let the driver know the page is done EndPage hdcPrinter Let the driver know the document is done EndDoc hdcPrinter Clean up the objects you created DeleteDC hdcPrinter DeleteDC hdcMemory ReleaseDC hWnd hdcWindow DeleteObject hbm if hPal DeleteObject hPal 2 21 8 Centering a dialog box in the screen Use the following code RECT rc GetWindowRect hDlg amp rc SetWindowPos hDlg NULL GetSystemMet rics SM_CXSCREEN rec right rce left GetSystemMetrics SM_CYSCREEN rc bottom rce top 0 0 SWP_NOSIZE SWP_NOACTIVATE eae N N 2 21 9 Determining the number of visible items in a list box In a list box if the number of lines is greater than the number of lines in the list box some of them will be hidden In addition it could be that the list box is an owner draw list box making the height of each line a variable quantity Here is a code snippet that will handle all
554. ter Example int d 10 int pint amp d 2 The number stored in pint is the memory location index where the integer d starts say 0x4202600 The size of each integer is 4 so the 3rd integer after 402600 starts at 0x4202608 If we want to find the fifth integer after 0x4202608 we add 20 5 sizeof int 20 and we obtain 0x420261C To increase a pointer by one means adding to it the size of the object it is pointing to In the case of a pointer to integer we add 4 to 0x204600 to obtain the next integer This is very often written with the shorthand pint or pint This is a short hand for Move the pointer to point to the next element Obviously this is exactly the same for subtraction Subtracting a displacement from a pointer means to point it to the lt nth gt element stored before the one the pointer is pointing to Id we have a pointer to int with a value of 0x4202604 making P means that we subtract 4 from the value of the pointer to make it point to the integer stored at address 0x4202600 the previous one To be able to do pointer arithmetic the compiler must know what is the underlying type of the objects That is why you can t do pointer arithmetic with void pointers the compiler can t know how much you need to add or subtract to get to the next element 1 15 1 2 Subtraction The subtraction of two pointers means the distance that separates two objects of the same type This distance is not
555. ter with the function fopen that returns a pointer to a FILE 3 Assignment to a specific address This happens in programs that need to access certain machine addresses for instance to use them as input output for special devices In those cases you can initialize a pointer to a specific address Note that this is not possible under windows or Linux or many operating systems where addresses are virtual addresses More of this later 4 You can assign a pointer to point to some object by taking the address of that object For instance int integer int pinteger amp integer Here we make the pointer pinteger point to the int integer by taking the address of that integer using the amp operator This operator yields the machine address of its argument 5 You can access the data the pointer is pointing to by using the operator When we want to access the integer pinteger is pointing to we write pinteger 7 108 C programming with Icc win32 This assigns to the integer variable indirectly the value 7 In lcc win pointers can be of two types We have normal pointers as we have described above and references i e compiler maintained pointers that are very similar to the objects them selves 2 References are declared in a similar way as pointers are declared int a 5 declares an integer a int pa amp a declares a pointer to the integer a int amp ra a de
556. th the argument the file we just created and that is all The two new keys will be automatically added to the registry Note the double backward slashes Obviously you should change the path to cmd exe to suit your system configuration 1 2 22 20 How do translate between dialog units and pixels When a application dynamically adds a child window to a dialog box it may be necessary to align the new control with other controls that were defined in the dialog box s resource tem plate in the RC file Because the dialog box template defines the size and position of a control in dialog box units rather than in screen units pixels the application must translate dialog box units to screen units to align the new child window An application can use the following two methods to translate dialog box units to screen units The MapDialogRect function provides the easier method This function converts dialog box units to screen units automatically For more details on this method please see the documentation for the MapDialogRect func tion in the Microsoft Windows Software Development Kit SDK Use the GetDialogBaseUnits function to retrieve the size of the dialog base units in pixels A dialog unit in the x direction is one fourth of the width that GetDialogBaseUnits returns A dialog unit in the y direction is one eighth of the height that the function returns For more details on this method see the documentation for the GetDialogBaseUnit
557. the stdio h header file You will notice that the name of the include file is enclosed within a lt gt pair This indicates the compiler that it should look for this include file in the standard include directory and not in the current directory If you want to include a header file in another directory or in the compilation directory use the double quotes to enclose the name of the file for instance include myfile h 2 We define a function called main that returns an integer as its result and receives no arguments void 1 All programs in C have a function called main and it is here that all programs start The main function is the entry point of the program 3 The body of the function is a list of statements enclosed by curly braces 4 We call the standard function printf that formats its arguments and displays them in the screen A function call in C is written like this function name argument list In this case the function name is printf and its argument list is the character string Hello n Character strings are enclosed in double quotes See page 50 for more on character string constants page 54 for function call syntax 5 The return statement indicates that control should be returned hence its name to the calling function Optionally it is possible to specify a return result in this case the integer Zero 9 InC only one return value is possible A functi
558. the internet wave required that each coffee machine in the world should have an internet connection Higher level interfaces were developed and added to the standard windows API Here is an example of a working program that will download the README file from the Icc win home q software solutions and write it to the disk of your machine in the current directory include lt stdio h gt include lt string h gt include lt windows h gt include lt direct h gt include lt wininet h gt static void ErrorOut char where int err GetLastError printf Error d 0x x when calling s n err err where int main void DWORD dwType FTP_TRANSFER_TYPE_BINARY HANDLE hConnect hOpen char szUser szPass szHost szFilel szFile2 hOpen InternetOpen FTPGET LOCAL_INTERNET_ACCESS NULL 0 0 if hOpen ErrorOut InternetOpen return 1 szHost www q software solutions com szUser anonymous szPass foo foo com hConnect InternetConnect hOpen szHost INTERNET INVALID _PORT_NUMBER szUser szPass INTERNET_SERVICE_FTP INTERNET_FLAG PASSIVE 0 if hConnect szFilel pub lcc README Advanced windows techniques 329 szFile2 README if FtpGetFile hConnect szFilel szFile2 FALSE INTERNET_FLAG RELOAD dwType 0 ErrorOut Ftp
559. the arguments to a function When you have a function prototyped like this void fn TYPE1 t1 TYPE2 t2 fn t2 The same rules apply as if you had written tl t2 1 13 8 The four operations This should be simple everyone should be able to understand what a b represents There are some subtleties to remember however 1 13 8 1 Integer division When the types of both operands to a division are one of the integer types the division per formed is integer division by truncating the result towards zero Here are some examples include lt stdio h gt int main void printf 5 6 d n 5 6 printf 6 5 d n 6 5 printf 6 5 d 6 5 d n 6 5 6 5 printf 23 6 d n 23 6 The output of this program is 5 6 0 6 5 1 6 5 1 6 5 1 23 6 3 1 13 8 2 Overflow All four arithmetic operations can produce an overflow For signed integer types the behavior is completely unspecified and it is considered an error by the standard Floating point types double or float for instance should set the overflow flag and this flag can be queried by the program using the floating point exception functions Most modern computers can distinguish between two types of overflow conditions 1 A computation produces a carry i e the result is larger than what the destination can hold 2 The sign of the result is not what you would expect from the signs of the operands a true overflow
560. the character is not there If we find it we stop searching and return the pointer to the character position char FindCharInString char str int ch while str 0 amp amp str ch str if str ch return str return NULL We loop through the characters in the string We use a while condition requiring that the char acter pointed to by our pointer str is different than zero and it is different than the character given In that case we continue with the next character by incrementing our pointer i e mak ing it point to the next char When the while loop ends we have either found a character or we have arrived at the end of the string We discriminate between these two cases after the loop How can this program fail We do not test for NULL Any NULL pointer passed to this program will provoke a trap A way of making this more robust would be to return NULL if we receive a NULL pointer This would indicate to the calling function that the character wasn t found what is always true if our pointer doesn t point anywhere A more serious problem happens when our string is missing the zero byte In that case the program will blindly loop through memory until it either finds the byte is looking for or a zero byte somewhere This is a much more serious problem since if the search ends by finding a random character somewhere it will return an invalid pointer to the calling program This is reall
561. the continuum leaving wide gaps between each number The range and precision of this subset is determined by the IEEE Standard 754 for the types float double and long double The qfloat and the bignum data types have their own formats 1 37 1 1 Float 32 bit format This format uses one bit for the sign 8 bits for the exponent and 23 bits for the fraction struct floatFormat unsigned Fraction 23 unsigned Exponent 8 unsigned sign 1 Bits 0 22 contain the 23 bit fraction f with bit O being the least significant bit of the fraction and bit 22 being the most significant bits 23 30 contain the 8 bit biased exponent e with bit 23 being the least significant bit of the biased exponent and bit 30 being the most significant and the highest order bit 31 contains the sign bit s The normalized numbers are represented using this formula Ds x 2 177 x Lf Here we have an exponent that uses 127 as bias This means that a constant is added to the actual exponent so that the number is always a positive number The value of the constant depends on the number of bits available for the exponent In this format the bias is 127 but in other formats this number will be different The range of this format is from 7f 7fffff to 00800000 in decimal 3 40282347e 38 to 1 17549435e 38 This numbers are defined in the standard header file lt float h gt as FLT_MAX and FLT_MIN The number of significant digits is 6 defined in float h as FLT_DIG 1
562. the incr statements and evaluate the test code again See for on page 13 switch expression case int expr Evaluate the given expression Use the resulting value to test if it matches any of the integer expressions defined in each of the case constructs If the statements comparison succeeds execute the statements in sequence beginning with that break case statement default If the evaluation of expression produces a value that doesn t match any of the statements cases and a default case was specified execute the default case statements in sequence See Switch statement on page 64 goto label Transfer control unconditionally to the given label Within the scope of a for do while loop statement continue with the next continue iteration of the loop skipping all statements until the end of the loop See Break and continue statements on page 63 break Stop the execution of the current do for while loop statement return expression return End the current function and return control to the calling one The return value of the function if any can be specified in the expression following the return keyword See page 61 1 11 7 Windows specific syntax Use the stdcall calling convention for this fi ti f ti inter th _stdcall A ee era E _stdcall fn void called function cleans up the stack See Stdcall on page 62 __declspec Export this identifier
563. then we compare that result with EOF In the second slightly more complicated we need a set of parentheses to force execution to execute the fgetc and the assignment first There is the danger that c would get assigned the result of the comparison of the fgetc result with EOF instead of the character itself Top down analysis 123 while c EOF count if c gt Frequencies c Frequency c fgetc infile return count The interface with the rest of the software for this function looks like this count ProcessFile infile Frequencies We could have avoided passing the Frequencies array to ProcessFile since it is a global vari able Its scope is valid when we are defining ProcessFile and we could use that array directly But there are good reasons to avoid that Our global array can become a bottleneck if we decide later to process more than one file and store the results of several files maybe combin ing them and adding up their frequencies Another reason to explicitly pass the Frequencies array as a parameter is of course clarity The Frequencies array is a parameter of this function since this function modifies it Pass ing it explicitly to a routine that modifies it makes the software clearer and this is worth the few cycles the machine needs to push that address in the stack When we write software in today s powerful micro processors it is important to get rid of the frame of mind of twenty y
564. ting for equality The if branch will be always taken because the result of that assignment is 6 what is different from zero The com piler will emit a warning whenever an assignment in a conditional expression is detected 1 3 3 Forgetting to close a comment If you write a b this is a bug c d c d will never happen The comment in the first line is not terminated It goes one through the second line and is fin ished with the end of the second line Hence the assignment of the second line will never be executed Wedit the IDE of lcc win helps you avoid this by coloring commentaries in another color as normal program text 1 3 4 Easily changed block scope Suppose you write the following code if someCondition fnl1 else OtherFn This is OK but if you add some code to debug for instance you end up with if someCondition fn1 else printf Calling OtherFn n OtherFn The else is not enclosed in curly braces so only one statement will be taken The end result is that the call to OtherFn is always executed no matter what Pitfalls of the C language 217 Golden rule ALWAYS watch out for scopes of if or else not between curly braces when adding code 1 3 5 Using the or more than once in an expression The ANSI C standard specifies that an expression can change the value of a variable only once within an expression This means that a statement like i
565. ting point number 50 0 This cast is not necessary at all and is there just for documentation purposes All integers when used in a double precision expression will be automatically converted to double precision by the com piler even if there is no cast The functions exp and tan are declared in math h Note that it is imperative to include math h when you compile this If you don t those functions will be assumed to be external functions that return an int the default this will make the compiler generate code to read an integer instead of reading a double what will result in completely nonsensical results 284 C Tutorial A break statement breaks the loop This statement means r r cos theta 5 and NOT r r cos theta CENTER In line 8 we use the rand function This function will return a random number between zero and RAND_ MAX The value of RAND_ MAX is defined in stdlib h If we want to obtain a random number between zero and 1 we just divide the result of rand by RAND_MAX Note that the random number generator must be initialized by the program before calling rand for the first time We do this in WinMain by calling srand unsigned time NULL This seeds the random number generator with the current time We are missing several pieces First of all note that CENTER is define CENTER 400 because with my screen proportions in my machine this is convenient No
566. tion and skip setting the size of the input and output buffers with SetupComm fSuccess GetCommState hCom amp dcb if fSuccess Handle the error printf GetCommState failed with error d n GetLastError return 2 Fill in DCB 57 600 bps 8 data bits no parity and 1 stop bit dcb BaudRate CBR_57600 set the baud rate dcb ByteSize 8 data size xmit and rcv dcb Parity NOPARITY no parity bit dcb StopBits ONESTOPBIT one stop bit fSuccess SetCommState hCom amp dcb if fSuccess Handle the error printf SetCommState failed with error d n GetLastError return 3 printf Serial port s successfully reconfigured n pcCommPort return 0 2 17 3 Files Besides the classical functions we have discussed in the examples Windows offers you more detailed file control for accessing file properties using asynchronous file input or output for managing directories controlling file access locking etc In a nutshell you open a file with CreateFile read from it with ReadFile write to it with WriteFile close the connection to it with CloseHandle and access its properties with GetFileAttributes Compared with the simple functions of the standard library those functions are more difficult to use since they require more parameters but they allow you a much finer control Here is a very small list of some of the file functions provided For mo
567. tion of the program In the second case it allocates the same amount of space but writes 67 into it and adds it to the initialized variables section 1 7 7 Statement syntax In C the enclosing expressions of control statements like if or while must be enclosed in parentheses In many languages that is not necessary and people write if a lt b run Not in C in C the if statement requires a parentheses if a lt b run The assignment in C is an expression i e it can appear within a more complicated expression if x z gt 13 z 0 This means that the compiler generates code for assigning the value of z to x then it compares this value with 13 and if the relationship holds the program will set z to zero 1 8 Errors and warnings It is very rare that we type in a program and that it works at the first try What happens for instance if we forget to close the main function with the corresponding curly brace We erase the curly brace above and we try h lcc examples gt lcc args c Error args c 15 syntax error found end of input expecting 1 errors O warnings 26 C programming with Icc win32 Well this is at least a clear error message More difficult is the case of forgetting to put the semi colon after the declaration of count in the line 3 in the program above D lcc examples gt lcc args c Error args c 6 syntax error found for expecting Error args c 6 skipping for Error args c 6 syntax er
568. tions for clearing the screen positioning the cursor at some line and column in the text screen etc You can also change the color of the text and modify the background 1 1 3 Statistics library This library provides a very complete set of statistics functions from the simple ones to the more complex ones Most of it uses the functions provided by the CEPHES mathematical library but adds a lot of other functions to it It follows for the naming of the functions the pro posal of Paul Bristow for the C language 1 1 4 Linear algebra library This library is based on the MESCHACH linear algebra package It helps you solve linear sys tems and many other things It accepts also sparse matrices and complex matrices The libraries of Icc win 209 1 1 5 Network utilities This is a small library but very useful It has functions like GetHttpUrl that allow you to get any file from the internet with a minimum effort Other things like ping and client server protocols are there See the Network chapter at the end of this tutorial for more information 1 1 6 Advanced math functions This library has been incorporated into the standard C library libc lib They are principally the elliptic functions Bessel functions psi Struve function and others Functions to evaluate a polynomial or find the roots of a polynomial have been added recently 1 1 7 Compression decompression functions This is the zlib library th
569. tips_class32 BaseBar tooltips_class32 BaseBar BaseBar tooltips_class32 Avance Sound Effect Control Panel AlcEaxCplClass tooltips_class32 tooltips_class32 NetDDE Agent NDDEAgnt tooltips_class32 H windowtree windowtreeWndClass a smallTextPopup t wedit windowtree d downloads windowtree windowtree c cIMDIFrame Timer ATL STATIC C tutorial doc Microsoft Word Opus pp Font OfficeTooltip Edit MsoCommandBarPopup Irfanv iew32 lt Clipboard gt 485 x 508 x BPP IrfanView32 How To Select a Window 32770 How To Select a Rectangle 32770 p Screen Capture WinCap Mame dM a bet Ee dee mle oe A lot of code is necessary to make this work but thankfully it is not our code but window s The window resizes redraws etc without any code from us 278 C Tutorial 2 10 7 Filling the status bar Our task consisted in drawing the tree but also of displaying some useful information about a window in the status bar when the user clicks on a tree item First we have to figure out how we can get notified when the user clicks in an item The tree control as many other controls sends notifications through its WM_NOTIFY mes sage We add a snippet of code to our MainWndProc procedure case WM_CREATE hwndTr CreateTr hwnd IDTREEWINDOW break case WM_NOTIFY return HandleWmNotify hwnd wParam lParam The function HandleWmNotify looks as follows
570. tle 124 The registry has been criticized because it represents a single point of failure for the whole system That is obviously true but it provides as a redeeming value a standard way of storing and retrieving configuration data and options It allows your application to use the same interface for storing this data instead of having to devise a schema of files for each application The software is greatly simplified by this even if it is risky as a general principle 266 C Tutorial MAKEINTRESOURCE IDD_ASK_PARAMS ghwndMain ParamsDlgProc break You give to that API the instance handle of the application the numerical ID of the dialog enclosed in the MAKEINTRESOURCE macro the handle of the parent window and the name of the procedure that handles the messages for the dialog You will need the prototype of the function in some header file to be able to use the name of it so it is a good idea to write a dlg boxprotos h header file that is included in every source file of the application If you want to pass a parameter to the dialog box procedure you can use DialogBoxParam 2 8 3 Drawing the window You have to answer to the WM_PAINT message See the documentation for a longer descrip tion This will provoke drawing when the window needs repainting only You can force a redraw if you use the InvalidateRect API You add code like this case WM_PAINT PAINTSTRUCT ps HDC hDC Begi
571. tory to the given one Its prototype is in lt direct h gt After changing the current directory we restore the argument argv 1 to its previous value using the same pointer p Note too that when we enter a backslash in a character constant enclosed in single quotes we have to double it This is because the backslash is used as within strings for indicating characters like n or others But this isn t a good solution We change the current directory instead of actually using the path information Changing the current directory could have serious consequences in the working of other functions If our program would be a part of a bigger software this solution would surely provoke more headaches than it solves So let s use our name field that up to now isn t being used at all Instead of passing a name to Fopen we will pass it a STREAM structure and it will be Fopen that will take care of opening the right file We change it like this FILE Fopen STREAM stream char name char mode FILE result char fullname 1024 p p strrchr stream gt Name if p NULL fullname 0 0 else p 0 strcpy fullname stream gt Name strcat fullname p strcat fullname name result fopen fullname mode if result NULL fprintf stderr Impossible to open s n fullname exit EXIT_FAILURE return result We declare a array of characte
572. tput being prepared to the compiler If it is NOT true then the preprocessor ignores all text until it finds the else or the endif This allows you to disable big portions of your program just with a simple expression like if 0 endif This is useful for allowing disabling portions of your program according to compile time parameters For instance lcc win defines the macro __LCC__ If you want to code some thing only for this compiler you write ifdef _ LCC Statements endif Note that there is no way to decide if the expression SomeFn foo Is a function call to SomeFn or is a macro call to SomeFn The only way to know is to read the source code This is widely used For instance when you decide to add a parameter to Cre ate Window function without breaking the millions of lines that call that API with an already fixed number of parameters you do define CreateWindow a b CreateWindowEx 0 a b This means that all calls to CreateWindow API are replaced with a call to another routine that receives a zero as the new argument s value It is quite instructive to see what the preprocessor produces You can obtain the output of the preprocessor by invoking lcc with the E option This will create a file with the extension i intermediate file in the compilation directory That file contains the output of the preproces sor For instance if you compile hello c you will obtain hello 1 1 34 1 Preprocessor
573. tring It contains two types of charac ters normal characters that are copied to the output without any change and conversion spec ifications that instruct the function how to format the next argument In the example above we have just the string hello n without any conversion specification so that character string is simply copied to the destination There should be always at least as many arguments to this functions as there are conversion specifications If you fail to do this with lcc win you will get a warning from the compiler Other compilers can be less user friendly so do not rely on that 1 14 1 Conversions A conversion specification begins with a percent sign and is made of the following ele ments 1 Zero or more flag characters 0 or space which modify the meaning of the operation 2 An optional minimum field width Note well this The printf function will not truncate a field The specified width is just that a minimum For instance the output of this program include lt stdio h gt int main void printf 5s n 1234567890 is 1234567890 and NOT 46 the quote char is specific to lcc win 76 C programming with Icc win32 12345 as expected If you want to specify a maximum field width you should use the precision field not the width field 7 3 An optional precision field made of a period followed by a number This is where you specify the maximum fie
574. tring instead of the compiler generated name Once this technical problems solved we see that our interface is much more flexible now We could just return FALSE from our interface function if the DLL wasn t there and thus disable some parts of the software but we wouldn t be tied to any DLL If the DLL isn t found the functionality it should fulfill can t be present but nothing more no catastrophes 115 In the documentation of windows you will find out that in the def file you can write other kinds of statements None of them are supported by Icc win and are silently ignored since they are redundant with the command line arguments passed to the linker Do not write anything else in the def file besides the names of the exports 116 The Macintosh works in the same manner albeit with a much more primitive system Amore formal approach 257 2 6 Amore formal approach 2 6 1 New syntax Now that we know how to make a DLL we should be able to understand more of C so let s come back again to the syntax and take a closer look A problem area is function pointer casting what leads straight into gibberish looking code int APIENTRY pfn char char int Better is to typedef such constructs with typedef int APIENTRY pfn char char int Now we declare our function pointer just with pfn pfnGetString and we can cast the result of GetProcAddress easily with pfnGetString pfn GetProcAddress
575. ts Casts as any other of the constructs above can be misused In general they make almost impossible to follow the type hierarchy automatically C is weakly typed and most of the weakness comes from casts expressions Many people add casts to get rid of compiler warnings A cast tells essentially to the compiler I know what I am doing Do not complain But this can make bugs more difficult to catch For instance Icc win warns when a narrowing conversion is done since the narrowed value could be greater than the capacity of the receiving type char c long m c m Possible loss of data It is easy to get rid of that warning with a cast But is this correct Some people in the C community say that casts are almost never necessary are a bad program ming practice etc For instance instead of void p int c char p they would write void p char cp p int c cp This is more of a matter of aesthetic Personally I would avoid the temporary variable since it introduces a new name and complicates what is otherwise a simple expression 43 Thanks to Keith Thompson for pointing me this fact 70 C programming with Icc win32 1 13 35 Selection A structure can have several different fields The operators and gt select from a variable of structure type one of the fields it contains For instance given struct example int amount double debt_ratio struct example Exm struct exampl
576. type those names our selves Without changing anything else we close the button properties and save our work We open the c source file generated by the editor 298 C Tutorial We obtain the following text Wedit Res Info ifndef _ windows_h include lt windows h gt endif include winexampleres h BOOL APIENTRY DlgSearch HWND hwnd UINT msg WPARAM wParam LPARAM lParam static WEDITDLGPARAMS WeditDlgParams switch msg case WM_INITDIALOG SetWindowLong hwnd DWL_USER DWORD amp WeditDlgParams DigSearchInit hwnd wParam lParam store the input arguments if any SetProp hwnd InputArgument HANDLE lParam break case WM_COMMAND switch LOWORD wParam case IDOK DigSearchOnOKSelected hwnd break break return HandleDefaultMessages hwnd msg wParam lParam We have here a normal callback procedure for our dialog It handles two messages WM_INITDIALOG and WM_COMMAND The callback procedures are in bold type There are two of them The initialization callback called DlgSearchInit and the one we attached to the OK button above Dl1gSearchOnOkSelected There are more things in there but for the time being we are interested in just those ones because they have to be written by you What you want to do when the dialog box has been created but it is not yet visible This is the purpose of the first callbac
577. u have a function like int fn int a the argument named a is copied into a storage area reserved by the compiler for the functions arguments Note that the function fn will use only a copy not the original value For instance int fnl int a a at7 return a int fn2 void int b 7 fn1 b return b 14 If this doesn t work or you receive warnings you have an installation problem unless you made a typing mistake Or maybe I have a bug When writing mail to me do not send messages like It doesn t work Those messages are a nuisance since I can t possibly know what is wrong if you do not tell me exactly what is happening Wedit doesn t start Wedit crashes The computer freezes The sky has a black color Keep in mind that in order to help you I have to reproduce the problem in my setup This is impossible without a detailed report that allows me to see what goes wrong Wedit will make a default project for you when you click the compile button This can go wrong if there is not enough space in the disk to compile or the installation of lcc win went wrong and Wedit can t find the compiler executable or many other reasons If you see an error message please do not panic and try to correct the error the message is pointing you to A common failure happens when you install an older version of Wedit in a directory that has spaces in it Even if there is an explicit warning that you sho
578. uff elif MACINTOSH Mac stuff elif WIN32 Windows stuff else error Unknown system endif Note the error directive This directive just prints an error message and compilation fails The lines that are in the inactive parts of the code will be completely ignored except of course preprocessor directives that tell the system when to stop Note too that the flow of the program becomes much difficult to follow This feature of the preprocessor can be abused to the point that is very difficult to see which code is being actually compiled and which is not The IDE of lcc win provides an option for preprocessing a file and showing all inactive lines in grey color Go to Utils the choose Show ifdefs in the main menu Note You can easily comment out a series of lines of program text when you enclose them in pairs of if 0 lines to be commented out endif 1 34 1 3 The pragma directive This directive is compiler specific and means that what follows the pragma is dependent on which compiler is running The pragmas that Icc wi32 uses are defined in the documentation In general pragmas are concerned with implementation specific details and are an advanced topic 172 C programming with Icc win32 1 34 1 4 The operator This operator allows you to concatenate two tokens define join a b a b a join anne bob When preprocessed this will produce a annebob This is useful for constructing va
579. uld NOT install it there most people are used to just press return at those warnings without reading them Then Icc win doesn t work and they complain to me I have improved this in later versions but still problems can arise 15 For understanding the rest of the output see the technical notes below 6 C programming with Icc win32 The fn2 function will always return 7 because function fnl works with a copy of b not with b itself This is known as passing arguments by value This rule will not be used for arrays in standard C When you see a statement like printf Hello n it means that the address of the first element is passed to printf not a copy of the whole character array This is of course more efficient than making a copy but there is no free lunch The cost is that the array can be modified by the function you are calling More about this later 1 3 3 Console mode programs and windows programs Windows makes a difference between text mode programs and windows programs In the first part of this book we will use console programs i e programs that run in a text mode window receiving only textual input and producing text output Those are simpler to build than the more complicated GUI Graphical User Interface programs Windows knows how to differentiate between console windows programs by looking at cer tain fields in the executable file itself If the program has been marked by the compiler as a console mode
580. ults 1 13 32 Address of operator The unary operator amp yields the machine address of its argument that must be obviously an addressable object For instance if you declare a variable as a register variable you can t use this operator to get its address because registers do not live in main memory In a similar way you can t take the address of a constant like amp 45 because the number 45 has no address 68 C programming with Icc win32 The result of the operator amp is a pointer with the same type as the type of its argument If you take the address of a short variable the result is of type pointer to short If you take the address of a double the result is a pointer to double etc If you take the address of a local variable the pointer you obtain is valid only until the func tion where you did this exits Afterward the pointer points to an invalid address and will pro duce a machine fault when used if you are lucky If you are unlucky the pointer will point to some random data and you will get strange results what is much more difficult to find In general the pointer you obtain with this operator is valid only if the storage of the object is pointing to is not released If you obtain the address of an object that was allocated using the standard memory allocator malloc this pointer will be valid until there is a free call that releases that storage Obviously if you take the address of a static or global
581. unc int prompt if result 1 strncpy destbuffer buffer bufferlen 1 destbuffer bufferlen 1 0 return result We have several things to explain here 1 We move the declaration of our static buffer that was before further down to the beginning of the file so that we can use this buffer in the GetString procedure to copy its contents into the destination buffer 2 We declare our flag for testing if the class has been registered as a static int i e an integer visible only in this module We do not need to initialize it to zero since the C language guarantees that all non explicitly initialized static variables will be set to zero when the program starts 3 We modify the declarations of local variables in the GetString procedure adding a result integer variable and a HANDLE that will hold the instance of the current module Before we received this as a parameter in the arguments of WinMain but now we have to get it by some other means The solution is to call the GetModuleHandle API to get this We indicate it that we want the handle of the currently running executable by passing it a NULL parameter 4 We test then our global flag classRegistered If it is zero we haven t registered the class and we do it now Afterwards we set the variable to one so that this piece of code will not be executed again 5 We call our DialogBox procedure just like we did before but now we assign its result to an
582. unction pointer member There are other function pointers in that structure for sure but we do not use them in this application We pass to that Free function a pointer to the interface it gave to us and then the object to free 136 Passing NULL works too 328 C Tutorial When we are done with a COM interface we have to remember to call a function to release it passing it again a pointer to the returned object We are done now we return the result and exit How can this program fail There are only three API calls here and all of them are tested for failure In principle there is no way this can fail although it could fail for other reasons it could provoke a memory leak for instance if we had forgotten the call to the Re lease method at the end or it could use resources that are never released the list of identifiers that we obtain from the system etc 2 18 3 Retrieving a file from the internet The basic way of receiving sending data in the internet is TCP IP a protocol originally devel oped for Unix systems and adapted later to windows by Microsoft under the name of win sock for window sockets The first versions of TCP IP for windows were very difficult to use and required a good deal of network programming knowledge the code for establishing an FTP connection under win dows 3 1 was several thousand lines and required watching each transaction and following each possible error This has changed a lot since
583. ur Frequencies array the new character frequen cies found The first function to be modified is checkargs We keep the interface with the calling function return NULL on error but we change the inner workings of it so that instead of calling fopen it calls findfirst STREAM checkargs int argc char argv STREAM infile NULL long findfirstResult struct _finddata_t fd if arge lt 2 printf Usage countchars lt file name gt n else findfirstResult findfirst argv 1 amp fd if findfirstResult lt 0 printf File s doesn t exist n argv 1 return NULL infile malloc sizeof STREAM infile gt Name argv 1 memcpy amp infile gt FindData amp fd sizeof struct _finddata_t infile gt File fopen fd name rb infile gt handle findfirstResult return infile We store in the local variable findfirstResult the long returned by findfirst We test then if smaller than zero i e if something went wrong If findfirst failed this is equivalent to our for mer program when it opened a file and tested for NULL But now comes an interesting part If all went well we ask the system using the built in mem ory allocator malloc for a piece of fresh RAM at least of size STREAM If this call fails there is no more memory left For the time being see later we ignore this possibility We want to store in there all the parameters we need to use the findfirst findne
584. urse to use the switch syntax and avoid the overhead of a function call Lec win allows you to do this with pragma density 0 This will modify the threshold parameter in the switch construction in the compiler so that a dense table of pointers is automatically generated for each case and all of the cases that aren t represented This is dangerous if your code contains things like case 1 case 934088 In this case the table could be a very bad idea This is a good technique for very dense switch tables only 178 C programming with Icc win32 There are many other uses of function tables for instance in object oriented programming each object has a function table with the methods it supports Since function pointers can be assigned during the run time this allows to change the code to be run dynamically another very useful application We have come up with a decent solution let s see what other might do include lt stdio h gt void print int n n amp amp print n 1 1 amp amp printf d n n int main int argc char argv print atoi argv 1 return 0 How does this work By using short circuit evaluation The statement n amp amp print n 1 1 amp amp printf Sd n n can be read from left to right like this If n is zero do nothing and return The second expression print n 1 1 calls print then yields 1 as its result This means that the third expression is evaluate
585. use malloc to allocate 12 pieces of RAM 357 913 942 bytes each Obviously the alloca tion should fail since it is much more than windows can allocate When we run this program however we see the following output s 12 n 357913942 s n 8 0x002d58c8 We see that s n is not 4 294 967 304 but 8 We have passed to malloc the number 8 instead of 4GB Imagine what will happen when we try to access that pointer that points to a memory area of just 8 bytes To avoid this kind of bad surprises it is better to pass the s and n variables to calloc instead that will take care of overflow 1 3 19 Programming style Style is one of the questions that regularly appear in the discussions in comp lang c For instance this routine written by R Heathfield Its object is to replace all points by an under score in a character string Mr Heathfield wrote char dot_to_underscore const char s char t malloc strlen s 1 if t NULL char u strcpy t s u t while u if u return t Mr Antonious Twink posted a message with the subject Bug Gross InEfficiency in Heath Field s fgetline program He said For some reason it makes thr passes through the string a strlen a strcepy then another pass to change dots when two would clearly be suffi cient This could lead to unnecessarily bad performance on very long strings It is also written in a hard to read and clunky style Pro
586. ut it isn t It took me quite a while to make an implementation that is at the same time easy to use and robust For instance what happens if the other side never answers It would be really bad if ping would freeze waiting for an answer that will never come Many other problems can occur and within the PingInterface structure there are a lot of fields that inform you what is going on The basic design principle is that you establish a callback function that is called by the ping function each time a packet arrives or a timeout is detected A more sophisticated usage of ping is the remake of the program of the same name Here is a possible implementation of that First we write a callback function to show progress in the screen as we receive a packet include lt ping h gt int PrintReport PingInterface Data if Data gt Errorcode WSAETIMEDOUT printf Timed out n return 1 printf sd bytes from s Data gt Bytes Data gt ip printf icmp_seq d Data gt Seq printf time td ms Data gt Time printf n return 1 This function is called by ping and just prints out the fields Note that we test the error code flag to see if we are being called because of a timeout or because of a packet arrived In this function we could send a message to a GUI window or we would update some pregress control etc The main function is now trivial We zero the i
587. uter if you are using a recent version of Icc win I improved error handling when I was writing this tutorial Input and output 27 But the most dreaded form of errors are the errors that happen at execution time i e when the program is running Most of these errors are difficult to detect they pass through the compila tion and link phases without any warnings and provoke the total failure of the software The C language is not very forgiving what programmer errors concerns Most of them will provoke the immediate stop of the program with an exception or return completely nonsense results In this case you need a special tool a debugger to find them Lcc win offers you such a tool and you can debug your program by just pressing F5 in the IDE Summary e Syntax errors missing semi colons or similar are the easiest of all errors to correct e The compiler emits two kinds of diagnostic messages warnings and errors e You can rise the compiler error reporting with the A option e The linker can report errors when an identifier is defined twice or when an identifier is missing a definition e The most difficult errors to catch are run time errors in the form of traps or incorrect results 1 9 Input and output In the Unix operating system where the C language was designed one of its central concepts is the FILE generalization Devices as varied as serial devices disks and what the user types in his her keyboard
588. variable the pointer will be always valid since the storage for those objects is never released Note that if you are using the memory manager gc making a reference to an object will pro voke that the object is not garbage collected until at least the reference goes out of scope 1 13 33 Sequential expressions A comma expression consists of two expressions separated by a comma The left operand is fully evaluated first and if it produces any value that value will be discarded Then the right operand is evaluated and its result is the result of the expression For instance p fn 2 3 6 The p variable will always receive the value 6 and the result of the function call will be dis carded Do not confuse this usage of the comma with other usages for example within a function call The expression fn c d 6 78 is always treated as a function call with three arguments and not as a function call with a comma expression Note too that in the case of a function call the order of evaluation of the different expressions separated by the comma is undefined but with the comma operator it is well defined always from left to right 1 13 34 Casts A cast expression specifies the conversion of a value from one type to another For instance a common need is to convert double precision numbers into integers This is specified like this double d int d In this case the cast needs to invoke run time code to make the actua
589. ve number that will interpret as a size_t ie as an unsigned integer This means that a negative request will be inter preted as an allocation request of more than 2GB Testing the result of an allocation allows a clean exit or an exception handling construct or other solutions that allow you to pinpoint with greater easy where the failure happened You should be aware of this problem when using flexible arrays When you write int fn int a int arrayl a 334 C Tutorial Here you are allocating a integers in the stack when control reaches the function prologue There is no way for you to check if this worked or not the only failure notification will be a stack overflow if a has the wrong value 2 20 Common errors 2 20 1 Dialog will not display when you add a control If you add a control that is implemented in comctl32 dll you need to always initialize the com mon controls before you open the dialog The best place is to do it at the start of the program in WinMain for instance You can use for the initialization either InitCommonControls or the newer primitive InitCommonControlsEx Some Coding Tips 335 2 21 Some Coding Tips Here are some useful receipts for solving specific windows problems 2 21 1 Determining which version of Windows is running BOOL InWinNT test for NT OSVERSIONINFO osv GetVersionEx amp 0Sv osv dwOSVersionInfoSize sizeof osv return osv dwPlatformId VER_PLATFORM
590. verloaded docalcs qfloat pq int overloaded docalcs double pd This function can receive either a qfloat number or a double number as input The compiler notices the type of argument passed in the call and arranges for calling the right function Notice that you define two internally different functions and that the decision of which one will be called will be done according to the type of arguments in the call It is not possible to declare a function overloaded after a call to this function is already gener ated The following code will NOT work docals 2 3 int overloaded docals double pd 81 This is a marker not a keyword The C standard forbids new keywords and this identifier is free to use in another contexts For instance you can still write int overloaded 123 Advanced C programming with Icc win 181 Here the compiler will signal an error It is also an error to declare overloaded functions with exactly the same parameter lists Note that the parameter lists can be the same even if they look different for instance int overloaded balance int newAmount int overloaded balance const int Both declarations are the same since the parameter names are of no importance Also the type qualifiers const volatile do not matter in this context 1 36 3 1 Advantages of overloading functions or operators 1 Provides incrementality since more overloading can be added at any time 2 It increases exp
591. wRect as the parent of the list box is the desktop window if bFirst hwndList HWND lParam HWND is 32 bits GetWindowRect hwndList amp rectList bFirst FALSE Resize listbox window cx by 50 use your size here MoveWindow hwndList rectList left rectList top rectList right rectList left 50 rectList bottom rectList top TRUE Call original combo box procedure to handle other combo messages return CallWindowProc lpfnOldComboProc hWnd message wParam lParam 2 22 17 How do I modify environment variables permanently You can modify user environment variables by editing the following Registry key HKEY_CURRENT_USER Environment You can modify system environment variables by editing the following Registry key 368 C Tutorial HKEY_ LOCAL MACHINE SYSTE CurrentControlSet Control Session Manager Environment BON ae BEE te Note that any environment variable that needs to be expanded for example when you use SYSTEM must be stored in the registry as a REG_EXPAND_SZ registry value Any val ues of type REG_SZ will not be expanded when read from the registry Note that RegEdit exe does not have a way to add REG_EXPAND_SZ Use RegEdt32 exe when editing these values manually However note that modifications to the environment variables do not result in immediate change For example if you start another Command Prompt after m
592. wanted to regenerate the import library for the DLL we could use this file together with the buildlib utility of lcc win to recreate the import library This can be important if you want to modify the names of the exported functions establish synonyms for some functions or other advanced stuff 254 C Tutorial 2 5 Using a DLL To use our newly developed DLL we just plug in the older test program we had done for our static library The interface is the same nothing has changed from the user code of our library The only thing that we must do differently is the link step since now we do not need to add the resource file to our program Wedit leaves our DLL in the Icc directory under the project main directory We just recompile our testdialog c program that we had before Here is the code for testdialog c again extern int APIENTRY GetString char prompt char buffer int len int main int argc char argv char buffer 1024 if GetString Enter a string buffer sizeof buffer printf String is s n buffer else printf User cancelled n return 0 We compile this in the directory of the project without bothering to create a project Suppose that our project is in h lcec projects dialog and the dll is in h lcc projects dialog lcc We compile with the command lcc testdialog c then we link with the command lcclnk testdialog obj lcc dialog lib Perfect We now type the name of the prog
593. we have to change the following things We have to initialize the name field of the array that now will be an array of structures and not an array of integers When each character is read we have to update the frequency field of the corresponding struc ture When displaying the result we use the name field instead of our count variable Here is the updated program include lt stdio h gt include lt stdlib h gt typedef struct tagChars int CharacterValue int Frequency CHARS CHARS Frequencies 256 Array of frequencies int compare const void argl const void arg2 CHARS Argl CHARS argl1 CHARS Arg2 CHARS arg2 Compare both integers return Arg2 gt Frequency Argl gt Frequency int main int argc char argv int count 0 FILE infile int c 118 C programming with Icc win32 if arge lt 2 printf Usage countchars lt file name gt n exit EXIT_FAILURE infile fopen argv 1 rb if infile NULL printf File s doesn t exist n argv 1 exit EXIT_FAILURE for int i 0 i lt 256 i Frequencies i CharacterValue i c fgetc infile while c EOF count if ce gt Frequencies c Frequency c fgetc infile fclose infile printf d chars in file n count qsort Frequencies 256 sizeof CHARS compare for count 0 count lt 256 count if Frequencies count Frequency
594. we want to start This is easy we ask the IDE Wedit about it using the Executable stats option in the Utils menu We get the following display 13 You start wedit by double clicking in its icon or if you haven t an icon for it by going to the Start menu run and then type the whole path to the executable For instance if you installed Icc win in c lcc wedit will be in c lcc bin wedit exe Hello 5 We see at the first line of the bottom panel that the program executable is called h lcec projects hello exe 2 We open a command shell window and type the command C gt h lcec projects lccl hello exe Hello C gt Our program displays the character string Hello and then a new line as we wanted If we erase the n of the character string press F9 again to recompile and link the display will be C gt h lcc projects lccl hello exe Hello c gt But how did we know that we have to call printf to display a string Because the documentation of the library told us so The first thing a beginner to C must do is to get an overview of the libraries provided already with the system so that he she doesn t waste time rewriting programs that can be already used without any extra effort Printf is one of those but are several thousands of pre built functions of all types and for all tastes We present an overview of them in the next section 1 3 2 What are function parameters When yo
595. were passed printf Usage countchars lt file name gt n else Call the _findfirst function with the name and info buffer findfirstResult _findfirst argv 1 amp fd Test result of findfirst and return immediately NULL if wrong if findfirstResult lt 0 printf File s doesn t exist n argv 1 return NULL Ask more memory to the allocator infile malloc sizeof STREAM Set the name of the new stream infile gt Name argv l1 Note the first argument of this call it s the address within the infile structure of the FindData member We take the address with the amp operator Since we are using a pointer we have to dereference a pointer i e with gt and not with the Note that the amp operator is used with the fd local variable to obtain a pointer from a structure member memcpy amp infile gt FindData amp fd sizeof struct _finddata _t infile gt file fopen fd name rb infile gt handle findfirstResult return infile void Initialize void this is the same as the function before int ProcessStream STREAM instream CHARS Frequencies int count 0 int c fgetc instream gt file while c EOF count if c gt Frequencies c Frequency c fgetc instream gt file return count Improving the design 129 void DisplayOutput CHARS Frequencies this is the same function as before STREAM
596. work The best approach is to leave this flag on at all times Obviously the executable size will be bigger since the information uses up space on disk If you do not want it you can instruct the linker to ignore it at link time In this way just switching that linker flag on again will allow you to debug the program The debug information generated by Icc win uses the NBO9 standard as published by Microsoft and Intel This means that the programs compiled with Icc win can be debugged using another debugger that understands how to use this standard Filling the blanks 289 In the Resources submenu we find a New item with several options in it We choose the dialog option The dialog editor builds an empty dialog and we are shown the following parameters dialog Properties Events DLG 0800 800 ooo Symbol value 800 Position 6 18 180 180 6 18 180480 Caption text Dialog Title Menu Class Font Font size 8 o ooo Oe Frame Border style Styles Oooo Advanced styles Even if this quite overwhelming we are only interested in two things the title of the dialog and the symbolic identifier We leave all other things in their default state We name the dialog IDD_SEARCH and we give it the title Text search After editing it looks like this Properties ets IDD SEARCH Symbol value Pasition Caption text Menu Class Font Font size Frame Border style Styles Advanced styles We pre
597. ws time formats can be easily obtained by using Windows functions such as FileTimeToSystemTime and File TimeToDosDateTime void UnixTimeToSystemTime time_t t LPSYSTEMTIME pst FILETIME ft UnixTimeToFileTime t amp ft FileTimeToSystemTime amp ft pst Exercises Explain this mystery include lt stdio h gt include lt unistd h gt include lt time h gt int main void time_t t1 t2 char st1 st2 tl time NULL if sleep 1 printf Signal received exiting n return 1 t2 time NULL printf tl is lu n unsigned long t1 printf t2 is Slu n unsigned long t2 stl st2 ctime amp t1 ctime amp t2 printf stl1 is s stl printf st2 is Ss st2 return 0 The code above gives this output t1 is 1183506197 t2 is 1183506198 stl is Wed Jul 4 01 43 18 2007 st2 is Wed Jul 4 01 43 18 2007 How can it happen that two outputs of ctime 3 given two different inputs t1 t2 are the same stl st2 Moreover on a shell console date r 1183506197 Wed Jul 4 01 43 17 CEST 2007 Using structures continued 163 date r 1183506198 Wed Jul 4 01 43 18 CEST 2007 1 33 Using structures continued C allows implementation of any type of structure Here is a description of some simple ones so you get an idea of how they can be built and used 1 33 1 Lists Lists are members of a more general type of objects called sequences i e
598. xParam API Looking into our program we see that the DialogBox API was called in our WinMain function see above We should modify this call then but a new prob lem appears where does WinMain know which string to pass to the DialogBoxParam API Well we could decide that this string would be the parameters passed to WinMain in the IpC mdLine argument This is the most flexible way We modify then the call to DialogBox like follows return DialogBoxParam hinst MAKEINTRESOURCE IDD_MAINDIALOG NULL DLGPROC DialogFunc int lpCmdLine Since our dialog box is now constructed with DialogBoxParam we receive in the lParam mes sage parameter the same pointer that we gave to the DialogBoxParam API Now we have just to set that text in the caption of our dialog box and it s done We do that again in our initial ization procedure by adding SetWindowText hDlg char 1Param The SetWindowText API sets the caption text of a window if that window has a caption bar of course To test this we have to tell Wedit to pass a command line argument to the program when it calls the debugger or executes the program with Ctrl F5 We do this by selecting the debugger tab in the configuration of wedit 4 File Edt Search Projest Jesoures ac IlnerCleassWem dials Linker Lang Ber Froect Help 111 We introduced that to see if we were really getting a string Since now we are returning that data to
599. ximum size the application will catastrophically fail with a stack overflow exception 146 C programming with Icc win32 2 There is no way to pass this memory block to a calling function Only functions called by the current function can see the memory allocated with this method 3 Even if the C99 standard is already several years old some compilers do not implement this Microsoft compilers for instance do not allow this type of allocation A work around is to use the _alloca function Instead of the code above you would write char workspace _alloca siz 1 30 3 Arena based allocation This strategy is adapted when a lot of allocations are done in a particular sequence of the pro gram allocations that can be released in a single block after the phase of the program where they were done finishes The program allocates a large amount of memory called arena and sub allocates it to the consuming routines needing memory When a certain phase of the pro gram is reached the whole chunk of memory is either marked as free or released to the operat ing system The windows operating system provides support for this strategy with the APIs CreateHeap HeapAlloc and others Advantages 1 Fewer calls to memory allocation deallocation routines 2 No global fragmentation of memory Drawbacks 1 Since the size of the memory that will be needed is not known in advance once an arena is full the strategy fails or needs to be com
600. xpression Meaning and value of result Example The value associated with that identifier see A ise deci closer view on page 49 an The value defined with this constant see Constants on page 49 Integer constant 45 45L 45LL constant Floating constant Sopi Aosa 45 9L 45 9Q character constant A L A String literal ba ao 3 constants Define tables or structure data 1 67 Integer constants 45 long integer constants 45L integer constants long long 64 bits integer constant 45LL or 45164 octal constant base 8 introduced with a leading zero 055 This is 45 in base 8 Hexadecimal constant introduced with 0x Ox2d this is 45 in base 16 Binary constant introduced with Ob This is an Icc win extension 0b101101 this is 45 in decimal his 4549 double precision constant K 4 59e2 eaten 45 9 or alt a 2 Float single precision constant 4 59e2f constants 45 9L or long doubl tant ong double constan 4 59621 qfloat constant This is an extension of lcc win 45 9q h t ai EE S char enclosed in simple quotes rar opg constant string literals enclosed in double quotes a string Array index Access the position index of the given array Indexes start at zero see Within the string the following abbreviations are recognized on page 51 Table 45 Array il i2 Access the n dimen
601. xt function pair with easy and we want to copy the finddata_t into our own structure and even put the name of the stream and a FILE pointer into it To do that we need memory and we ask it to the mal loc allocator Once that done we fill the new STREAM with the data e we Set its name using the same pointer as argv 1 e we copy the fd variable into our newly allocated structure and e we set the file pointer of our new structure with fopen so that we can use the stream to read characters from it Another alternative to using the built in memory allocator would have been to declare a global variable call it CurrentStream that would contain all our data We could have declared some where in the global scope something like STREAM CurrentStream and use always that variable 126 C programming with Icc win32 This has several drawbacks however the bigger of it being that global variables make follow ing the program quite difficult They aren t documented in function calls they are always passed implicitly they can t be used in a multi threaded context etc Better is to allocate anew STREAM each time we need one This implies some memory man agement something we will discuss in depth later on Now we should modify our ProcessFile function since we are passing to ita STREAM and not a FILE This is easily done like this int ProcessFile STREAM infile CHARS Frequencies int count 0 int c fgetc
602. y If you have an array of pointers to structures you use array index gt field 4 If you have an array of structures you use array index field 5 If you are interested in the offset of the field i e the distance in bytes from the beginning of the structure to the field in question you use the of fSetof macro defined in stddef h offsetof structure or typedef name member name For instance to know the offset of the Frequency field in the structure CHARS above we would write offsetof CHARS Frequency This would return an integer with the offset in bytes 120 C programming with Icc win32 1 22 Identifier scope and linkage Until now we have used identifiers and scopes without really caring to define precisely the details This is unavoidable at the beginning some things must be left unexplained at first but it is better to fill the gaps now An identifier in C can denote e an object e a function e atag or a member of a structure union or enum e a typedef e a label For each different entity that an identifier designates the identifier can be used is visible only within a region of a program called its scope There are four kinds of scopes in C The file scope is built from all identifiers declared outside any block or parameter declaration it is the outermost scope where global variables and functions are declared A function scope is given only to label identifiers The block scope is built from all
603. y with his proposal for the C language 119 Remember the basics of Boolean logic a bit ANDed with another will be one only if both bits are 1 A bit Ored with another with return only if one or both of them is 1 A more advanced window 259 mary menu and nothing else Well this is the skeleton of a windows application Let s see it in more detail We start as always in the same place We go to the WinMain function and we try to figure out what is it doing Here it is int WINAPI WinMain HINSTANCE hiInstance HINSTANCE hPreviInstance LPSTR lpCmdLine INT nCmdShow MSG msg HANDLE hAccelTable Saves in this global variable the instance handle that must be passed as an argument to many window functions hinst hInstance f the initialization of the application fails WinMain exits if InitApplication return 0 Loads the keyboard accelerators for common menu options hAccelTable LoadAccelerators hInst MAKEINTRESOURCE IDACCEL Creates the main window and exits if it can t be created if hwndMain CreateApplWndClassWnd HWND 0 return 0 Creates the status bar at the bottom of the main window CreateSBar hwndMain Ready 1 Shows the main window ShowWindow hwndMain SW_SHOW Starts the message loop When the main window post the quit message GetMessage will return NULL while GetMessage amp msg NULL 0 0 if TranslateAccelerator msg hwnd hAccelTa
604. y work is done we have to figure out now an efficient organization for our word table We have the following requirements 1 It should provide a fast access to a word to see if a given sequence of characters is there already 2 It should not use a lot of memory and be simple to use The best choice is the hash table We use a hash table to hold all the words and before entering something into our hash table we look if is in there already Conceptually we use the follow ing structure 154 C programming with Icc win32 Slot word table lists of VVORDLIST structures Our word table is a sequence of lists of words Each list is longer or shorter depending on the hash function that we use and how good our hash function randomizes the input If we use a table of 65535 positions slots and a good hash algorithm we divide the access time by 65535 not bad To enter something into our table we hash the word into an integer and we index the slot in the table We then compare the word with each one of the words in the list of words at that slot If we found it we do nothing else than increment the count of the word If we do not find it we add the word at the start of that slot Note that this requires that we define a structure to hold each word and its associated count Since all the words are in a linked list we could use the following structure borrowing from the linked list representation discussed above typedef struct _Wo
605. y 308 Enumerating registry subkeys 309 Rules for using the registry 311 Interesting keys 312 Etc 313 Clipboard 314 Serial communications 315 Files 316 File systems 317 Graphics 318 Handles and Objects 318 Inter Process Communications 318 Mail 319 Multimedia 319 Network 319 Hooks 319 Shell Programming 320 Services 320 Terminal Services 320 Windows 321 Advanced windows techniques 322 Memory mapped files 322 Letting the user browse for a folder using the shell 325 Retrieving a file from the internet 328 Opening a web site or an HTML file using the default browser 329 Creating a desktop shortcut 329 Error handling under windows 331 Check the return status of any API call 333 Always check allocations 333 Common errors 334 Dialog will not display when you add a control 334 Some Coding Tips 335 Determining which version of Windows is running 335 Translating the value returned by GetLastError into a readable string 335 Clearing the screen in text mode 335 Getting a pointer to the stack 336 Disabling the screen saver from a program 336 Drawing a gradient background 337 Capturing and printing the contents of an entire window 337 Centering a dialog box in the screen 340 Determining the number of visible items in a list box 340 Starting a non modal dialog box 341 Displaying the environment variables 341 Propagating environment variables to the parent environment 342 Restarting the shell under program control 342 Translating client coor
606. y are used Static These controls do not send any notifications hence they are called static They are text strings or lines rectangles Rich edit controls They are used to display text with more than a single font or color They have a long list of notifications you can even specify that you want to be notified when the user clicks in an URL in the text This control uses both the WM_COMMAND interface and the WM_NOTIPY interface The interface using the WM_COMMAND message was described above See page 273 Another interface used by many controls is the WM_NOTIFY interface This message has the following format 1lResult SendMessage returns LRESULT HWND hWndControl handle to parent window UINT WM_NOTIFY message ID WPARAM wParam WPARAM int idCtrl LPARAM lParam LPARAM LPNMHDR pnmh i This code is executed by the control when it sends a message to the parent window The important parameters of this message are 1 idCtrl This is a numerical constant an integer that is used as the ID of this control 2 pnmh This is a pointer to a structure that contains further information about the message It points to a NMHDER structure that contains the following fields typedef struct tagNMHDR HWND hwndFrom UINT idFrom UINT code NMHDR 270 C Tutorial 3 This struture can be followed by more data in some of the notifications that a control can send In that c
607. y bad news since the calling program may not use the result immediately It could be that the result is stored in a variable for instance and then used in another completely unrelated section of the program The program would crash without any hints of what is wrong and where was the failure Note that this implementation of strchr will correctly accept a zero as the character to be searched In this case it will return a pointer to the zero byte 1 17 2 strlen Return the length of a given string not including the terminating zero This is solved by the strlen function We just count the chars in the string stopping when we find a zero byte int strlen char str 90 C programming with Icc win32 char p str while p 0 ptt return p str We copy our pointer into a new one that will loop through the string We test for a zero byte in the while condition Note the expression p 0 This means Fetch the value this pointer is pointing to p and compare it to zero If the comparison is true then we increment the pointer to the next byte gt l We return the number of characters between our pointer p and the saved pointer to the start of the string This pointer arithmetic is quite handy How can this program fail The same problems apply that we discussed in the previous example but in an attenuated form only a wrong answer is returned not an outright wrong pointer The program will only stop at a
608. y initialized and loading of the program can continue or zero meaning a fatal error happened and the DLL is unable to load itself Note that we return always TRUE even if our registration failed Why If our registration failed this module will not work The rest of the software could go on run ning however and it would be too drastic to stop the functioning of the whole software because of a small failure in a routine that could be maybe optional Why the registration of our class could fail One of the obvious reasons is that the class is already registered i e that our calling program has already loaded the DLL and it is loading it again Since we do not unregister our class this would provoke that we try to register the class a second time For the time being we need to handle only the event when the DLL is loaded or unloaded We do two things when we receive the DLL_PROCESS_ATACH message we store away in our global variable the instance of the DLL and then we register our string dialog box class We could have just done it in the LibMain function but is clearer to put that code in its own rou tine We write then static void DoRegisterClass void Dynamically linked libraries DLLs 253 WNDCLASS wc memset amp wc 0 sizeof wc we lpfnWndProc DefDlgProc wce cbWndExtra DLGWINDOWEXTRA we hInstance hinst we hCursor LoadCursor NULL IDC_ARROW wce hbrBackground HBRUSH COLOR_WINDOW 1 we lp
609. y to restart the shell To do this find the window of the Explorer send it a quit message and restart it The following code snippet will work HWND hwndShell FindWindow Progman NULL PostMessage hwndShell WM_QUIT 0 OL WinExec Explorer exe SW_SHOW 2 21 14 Translating client coordinates to screen coordinates To determine the screen coordinates for the client area of a window call the ClientToScreen function to translate the client coordinates returned by GetClientRect into screen coordinates The following code demonstrates how to use the two functions together RECT rMyRect GetClientRect hwnd LPRECT amp rMyRect ClientToScreen hwnd LPPOINT amp rMyRect left ClientToScreen hwnd LPPOINT amp rMyRect right 2 21 15 Passing an argument to a dialog box procedure You can pass a void to a dialog box procedure by calling result DialogBoxParam hInst Instance of the application MAKEINTRESOURCE id The resource ID or dialog box name GetActiveWindow The parent window Some Coding Tips 343 Digfn The dialog box procedure DWORD Hello The arguments In your dialog box procedure here DlgFn you will find those arguments in the IParam parameter of the WM_INITDIALOG message 2 21 16 Calling printf from a windows application Windows applications do not have a console i e the DOS window To access the console from a Wi

Programming with lcc-win

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