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C Vu Volume 1 Issue 5 PDF

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1. is e POINTEX2 C x jx Objectives Kj o declaration of a pointer o use of amp address of operator to a initialise a pointer EJ o use of pointer variable name to either assign value to or read contents of x JR pointer variable a o use of contents of operator to read x contents of object that pointer points to Jx Compiler Prospero C ay Machine Atari ST Reference Article The Dreaded Pointer y Part 1 By Phil Stubbington Ef 35 Volume 1 C Vu Volume 1 Issue 5 July 1989 include lt stdio h gt include lt stdlib h gt include lt assert h gt void main int Count Increment 4 Declaring A Pointer To An Integer int PtrToInt NOTE as PtrToInt is an auto as are Count and Increment gibberish until we initialise it assert sizeof long sizeof int 4 Using Pointer Variable Name To Assign Value To Pointer Variable Using amp Address Of Operator To Initialise A Pointer PtrToInt amp Count now PtrToInt contains the address of Count Count Increment printf Count print pu ge ts tchar i e it points to it S232 97 gd n tAddress of m Using Pointer Variable Name To Read Contents Of Pointer Variable Using Contents Of Operator To Read font enta i Object That Pointer Points To
2. F PtrToInt 1X n tContents of PtrToInt PtrTolInt Press Return Enter key to exit Count UPA ye E 1X n ma rToInt W x class variable it contains xf Issue 5 af Count amp Count sd n If you now compile link and execute the program what results do you get What you should have got is something like this Count 32 Address of Count 35718 PtrToInt 35718 36 Volume 1 Issue 5 Contents of PtrToInt 32 In other words count is 32 no great surprises there I hope The address of the variable Count is x The value in the pointer variable PtrToInt is also x Finally because PtrToInt contains the address of count the contents of that address should be the same as the variable Count i e 32 Is That It Well no it isn t What we have covered in this short article are some of the fundamentals of pointers We ve seen that we can use the address of operator amp to find the address of a variable We ve declared a pointer by telling the compiler what type of variable the pointer points to and giving the pointer a name prefixed by an asterisk to indicate that it is a pointer We ve seen that using just the pointer name can be used to either assign an address to the pointer or read the pointer address itself Finally we ve seen that prefixing the pointer name with an asterisk outside of the initial declaration can be used
3. A good procedure In C we can pass as many parameters as we like or none We can return only one value of any type or none Functions can be 0 to n lines long where n tends to infinity Function name lengths vary with the compiler but typically can be up to 31 characters long i bi a c zz q t ty s 11 locate_nearest_ Eseries _value res series Both i and ii would be legal function specifications in C Which is the more readable Accepted function names longer than more than 15 or so characters are a bit verbose but look at the possibilities Hardly any comments needed In ii we have used a structure to gather closely related information about a data type We pass our basic data and also a further parameter to control or determine the action of the function This may be a simple TRUE FALSE flag or a pointer to an array of values Passing a control parameter like this is a good idea It allows you to code the function in a way which caters for future updates It allows a single function to carry out different yet related tasks It allows us to include optional conditions in the function which we can switch on or off according to how we call it e g e annunciate out of range values e perform rounding upwards 18 Volume 1 Issue 5 e display error or remain silent A control parameter like this is often best placed first in the argument list Why Well in C if we don t ask for other parameters th
4. Bryan Hopkins Membership 8906 is also on a quest this time for some information on graphics file formats I am interested in writing some software which requires the use of files created by various graphics packages chiefly PC Paintbrush and GEM Draw So far I have been unable to work out how the files these packages produce can be read to the 45 Volume 1 Issue 5 screen Possibly someone else in the group has solved this problem already and would be willing to pass the information on Any assistance gratefully received Writing For C Vu sub titled How to keep the editor happy As you can see by flicking through any issue of C Vu the group relies heavily on a small group of members who make the effort to contribute which is after all what a user group is all about If every member of the group made the effort to write something for C Vu then we would have enough material for many issues to come Although articles are always welcome within the group we have many members who can help with your technical queries either about C itself or related to the operating system environment you are using At present we have members who can help out with technical queries on MS DOS OS 9 Unix Xenix Mirage TOS including GEM Minix Submissions for C Vu should be in the form of ASCII text files on a 3 1 2 or 5 1 4 standard MS PC GEM DOS format disk 5 1 4 BBC Micro format DFS or ADFS single sided single densi
5. In many cases however an application initiated redraw happens because of a computed change for instance a spreadsheet update and its timing is not crucial In this instance you may wish to have the app send ITSELF a redraw request The main advantage of this approach is that the AES is smart enough to see if there is already a redraw request for the same window in the queue and if so to merge the requests by doing a union of their rectangles In this fashion the blinky appearance of multiple redraws is avoided without the need to include logic for merging redraws within the program A utility routine for sending the self redraw is included in the down load for this article WINDOW CONTROL REQUESTS An application is notified by the AES via the message system when the user manipulates one of the window control points Remember that you must have specified each control point when the window was created or will not receive the associated control message The most important thing to understand about window control is that the change which the user requested does not take place until the application forwards it to the AES While this makes for a little extra work it gives the program a chance to intervene and validate or modify the request to suit A second thing to keep in mind is that not all window updates cause a redraw request to be generated for the window because the AES attempts to save time with raster moves on the scree
6. The problem arises because we can see that copydir may have to loop through several files and possibly subdirs before it returns The application may be text based windows file based who knows And why should the engine have to know Informing the Application We have several alternatives open to us 1 We can make the variables that the copydir function uses external and therefore accessible to other modules We could then have copydir call an application level function to do whatever it wants with this externally available information 2 We could call a function at appropriate stages and pass parameters with the current information The application module could do what it liked with these parameters Both of the above methods mean that we must hard code the name of the function from the application module into our copydir function This makes it less general and is something we may not want to do 3 Alternatively we could pass a pointer to a function into copydir then we don t need to hard code it s NAME but we still need to know all about the parameters so we are still hard coding here little gain really in this case What we really want is a way to control the execution of copydir and get status from it without changing the way it works In a multitasking system this is no problem but in a single task system like ours it s a bit more awkward 25 Volume 1 Issue 5 Method 2 is chosen here cal
7. Phil Stubbington scccscencaxcaiicaeaces 32 One Person s View by Francis GlassboroW seseseeseesseeses The Source LADTALY ncacievanvcs metic ces Order POM beisctsusesnsnrieesscrsnwod ess aaenntians Why Programming Why C by Donald Wilcock eeeeeeeeeeeeeee Scientific Magic Circle ce ceeseeseees DSUICES iasasvesstivodetiate eea aa R Writing For C Vu eessseseesesssseserssesresseee Megamax Laser C by Phil Stubbington 0 00 ee Standard Watching by Neil Martinin aaaea The Numerical C Extensions Group by Rex Jacsch etre sacvciasesueiecsienteeuniees Copyright amp Things ceceeeeeeeeeees ISSUE 6 DEADLINE ccsccsccecceseesees eee 45 Volume 1 Issue 5 Wotz Nu by Phil Stubbington More things to spend your or preferably someone else s money on The South West Software Library Definitely the cheapest thing to tell you about this month is the latest catalogue Number 3 from the South West Software Library Dealing exclusively in public domain shareware software for the Atari ST the S W S L are the only professional P D library I know of The twenty page catalogue contains numerous hints and tips for getting the software to work on your system In addition the library will do as much as humanly possible to solve any compatibility problems for you no guarantees though They also offer upgrades either for free if you order other disks at the same time
8. This has a unpleasant side effect of the file having a different size to the number of bytes read or written So never use stat or fstat to predict the number of bytes to read but use return value of read or feof to detect end of file Also read may return less bytes than were asked for when not at the end of file In binary mode no translation will take place so that binary data can be read or written but this may have weird effects if you attempt to read or write text files Text mode is normally the default mode although some compilers allow the default to be changed and there is usually a method to set text or binary mode on a per file basis The method of setting the mode on a file is normally done by a modifier to the open mode Microsoft C5 1 uses O_BINARY or O_TEXT for open and b or t for fopen For example fopen textfile rt or open file bin O WRONLY O BINARY Text mode also slows down file i o so it is best to use binary mode if you want to obtain benchmark timings Process Control This area is almost entirely dependent upon the O S About the only portable function is the system call In general it is best to avoid process control functions if possible Hardware If a program is to be kept portable it SHOULD NOT make any assumptions about what hardware is present this includes screen management 10 Volume 1 Issue 5 Console I O Ideally all console I O should be done with
9. again Otherwise known as a slope shoulder job Some interesting points arise in this function What happens if the target disk get s full up We need to ask for a new one Not just that but this 24 Volume 1 Issue 5 might have happened three or four levels down in subdirectories we need to create them on the new disk before we can proceed Also in a friendly application it s nice to see what s going on during lots of disk crunching and if possible allow the user to exit in a graceful way I just hate programs that don t forgive my mistakes The solution to the first problem requires creation of a function which will do what DOS doesn t let you do create several nested subdirectories at once Create directory create_dir create_dir accepts the name of a path to build and parse out the names one by one creating the subdirs as it goes If it gets into difficulties it returns a fail code Although slightly restrictive on the passed string this is a useful stand alone function And we might we expect that copydir should be useful stand alone apart from the second problem we identified This opens up a question which arises for me time and again in application programs On the one hand we want to make these engine functions as I call them as general as possible so we can use them on the next job On the other we need to tie back up to the application level somehow to let it know how things are going
10. be quite acceptable All such boundary conditions must be clearly commented and documented Length If a function has stretched to more than 70 or 80 lines then look at it closely for blocks of statements which form natural sub activities No matter if this sub block is never called again it is likely to improve the legibility of the program Sometimes a function with multiple case statements and lots of comments may stretch to 100 lines This should be considered exceptional A fine length for a function is one which fits on a single form of printout paper We ll continue next time with some talk about exit codes and function return types The Story Behind FLIT by Colin Masterson I describe FLIT as a multiple media disk copying program which replaces the tedium of creating temporary directories and transferring files in and out of them when copying This is the background of it s development with a look inside at some of the functions which may be of interest to DOS users The Background I move around a lot I work in offices at home offshore here there everywhere The IBM standard has been great for me WITHOUT IT the type of work I do would NOT be possible WITH IT it s just a hassle The hassle part comes from the fact that I m always moving files from one machine to another and copying disks from one format to another For a while I only had 5 25 disk to worry about now I ve got 3 5 ones too One thing that rea
11. code amongst their wide selections but the CUG library is specially dedicated to making source code available for programmers to develop with rather than being a source of ready to run free programs This feature makes the library useful to people with a wide range of machines and interests If you have a machine with a C compiler that is able to read one of the disk formats the library is offered on then we have something to offer you Many other library services cater only for the strict IBM PC clone market The CUG library does not care if you have a PC an Atari an Apricot an Archemedies or even a Unix system The two disk formats that the library directly supports are the PC 360k standard for 5 1 4 disks and the 720k double sided 3 1 2 format used by IBM PS 2 Apricot Atari and most of IBM compatible portables Single sided variants of the above formats are also available if requested specifically To read a library disk you will need to be able to understand Microsoft MS DOS disk format WITH sub directories i e DOS 2 0 or above The library disks will use sub directories to partition files into groups that belong together If a program has more than one source file it will generally have a directory to itself unless it is obvious which files belong together No form of archiving or packing will be used on the library disks This removes the need to have a version of ARC or similar that runs on your machine One exception to this is that
12. from CGA to VGA and even Hercules monochrome graphics However compared with most commercial graphics libraries Microsoft s offering is slightly limited Text can only be output at text screen coordinates and no text styles are supported CodeView The CodeView debugger is much larger than it s earlier incarnations it weighs in at over 200k and takes minutes to load from floppy as it now tries to cater not only for C programmers but for BASIC Pascal FORTRAN and assembler programmers too The expression evaluator is different for each mode hence the increased size It now handles 80386 code and lets you debug overlays It is still my favourite debugger and a far cry from those old days on the Harris minicomputer when I had to printfQ every function to track down the bugs In order to debug your source code with CodeView you need to add a compiler switch when you invoke the compiler If you link your program separately you will also need to tell the linker to add CodeView debugging information onto the end of your executable file As a consequence such files are much larger than normal If your program is very large then CodeView may not be able to load the whole program even if MS DOS can To get round this Microsoft now include a CVPACK utility which optimises the debugging information in the executable file On one test 32654 bytes of debugging info was packed to 3856 byte just by running CVPACK An enhancement to the old CodeV
13. from September that completely changes with the introduction of Corporate or Group membership The idea behind this is to get C Users meeting talking and providing mutual support and encouragement There will be a single corporate membership fee that is independent of the number of people making up a group During the summer I will be putting together a package of material for use by members who want to start their own local group and we hope that you all will This package will be based on the experience of the Oxford and District C User Group which grew out of the very successful C Programming Workshop that is run by the North and West Oxford Community Education Committee The package will include 1 Advertising posters and other promotional material to help you get started 2 A draft constitution just something simple to keep you legal 3 Suggestions about who to contact for help in all aspects of developing a local group 4 Ideas on running a programming workshop 5 Running your on branch of the National CUG source code library If you have any other ideas about things that would help in getting a local group started please contact me so that they can be included The pack will be ready for the PC Show but earlier notification of interest would be welcome and encouraging C Programming Workshop From September 1988 till March 1989 I ran a programming workshop on monday evenings at a local school About a dozen people turned up regul
14. hoped that the work done by group members on the software that comes into the library will improve this situation UPDATING THE LIBRARY The initial offerings in the library have mostly been culled from the offerings of other shareware libraries amp BBS downloads Some material has been donated by CUG members At the moment organisation of the library is in its early stages and the quality of the software patchy I have endeavoured to cut out on duplication and the banal leaving a reasonable base of material on which to build a strong UK Public Domain resource If you have taken one of the programs from the library and have made significant improvements to it then you may re submit the improved version for inclusion to the library Any improved versions of the library programs will be made available to the membership as separate volumes will full acknowledgement to the member who has done the improvement work The original version will remain available as the original volume number In this way the development of the programs under out control can be traced and the same program can be allowed to branch off into many separate development paths Anybody submitting an improved version of a library program will be entitled to an equivalent amount of new library material at no charge If you indicate that you would like to be put in touch with other members that are working with the same program then this can be arranged through the pages of C Vu a so
15. ina README DOC file how this can be overcome The compiler is closer to the proposed ANSI standard than previous incarnations but some features are still unsupported The volatile declarator is implemented syntactically but not semantically Trigraphs are not included but then they would be redundant as the IBM environment supports the full 8 bit ASCII character set However most other features are fully supported including the use of as single line comment delimiter New pragmas allow changing the source and object code listing format and placing comments into the object file While testing this I found a bug The string pragma comment lib mylibry mentioned in the manual will not compile If it had worked the lib comment type would allow the user to select from the source code a library to be included at link time Other features include error to output an error message new predefined macro names DATE TIME STDC and TIMESTAMP _ the use of macros in include and line directives and ellipsis in function prototypes to specify that the function takes a variable number of arguments All these features can be disabled via a command line option if portability to non ANSI compilers is an issue Quick C As a result of the recent publicity most people have probably heard of the Microsoft Quick C development environment This integrates a full screen editor with a fast in memory C compiler debugger linker an
16. less than you do listen to them with respect but do not let then overawe you One day you will know something they don t Well thats it from me Why don t you have a go Tell us something about your experience of C Tell us what you use it for Tell us what you would like to know about Send in your favourite function Whatever you do don t just sit there and hope someone else will provide something for you to read on the next wet afternoon If you do you will simply have to put up with more from me and the rest of the ODCUG lot All the best for now hoping to see lots and lots of you at the PC Show this Autumn 40 Volume 1 Issue 5 The Source Library The Source Library is intended to be a collection of C source code in the public domain brought together so that any member of the C Users Group U K can user and develop it as an aid to their own learning and enjoyment and to improve the stock of C source T Software Tools 1 bracket and comment checkers structure analysers three variations upon the XREF theme several hex loaders and dumpers time command execution Games 1 principally the AdvSys adventure writing system with all sources documentation and a sample adventure Also contains the Towers of Hanoi and Conways Life Editors one of the latest version of the MicroEmacs editor with sources and extensive documentation Now contains a macro languag
17. of the EXE files have been generated from the sources by myself The library does not at present cover the Apple Mac or any of the CP M formats including Amstrad P C W If you have one of these machines then contact me and I can arrange transfer of the volume of your choice by modem This will be for the same charge as the disk would be but you will also have to pay the phone bill Another alternative would be for you to find a friend with a machine that can read one of the disk formats and do a serial transfer over a direct RS232 line HOW IT WORKS The way the library works is that any C code donated to the library will be catalogued and a CUG Library header comment prepended to the file This comment reproduced below is intended to allow the change history of the file while in CUG hands to be recorded It is hoped that any CUG member that improves a library program will re submit it to the library so that all may benefit from the work they have done In this way all may learn together and produce good software for the benefit of all Here is a sample comment anything between lt and gt is variable information ROR KKK KKK KR KK KK KKK kkk K kk kK k k kk RK k K k k k k RK KK OR KK k C Users Group U K C Source Code Library File lt disk num gt Inquiries to M Houston 36 Whetstone Clo Farquhar Rd Edgbaston Birmingham B15 20N ENGLAND x KKKKKKKKKKKKKKKKKKKKK KKK KKK KKKKKKKKKKKKKK KKK KKKKKKKKKKKK
18. reason for this is that the old FCB call is actually much faster since it allows the use of wild cards There is no equivalent in the new calls as far as I can see There is a bit more fancy footwork in count_files to handle read only files but not much With the careful use of the mode flag the KILLDIR program simply adds a user interface some protection and two calls to count files The first call lists the subdirs and the number of files in each the second call does the actual dirty work Rea ie Volume 1 Issue 5 Be warned Notice the use of the word protection with reference to count_files I coded KILLDIR to place a number of restraints on its use since it s a potentially lethal function It will quite merrily delete your entire disk without a whisper if you ask The protection I added in KILLDIR was e Deletion of the root prohibited e Deletion from another drive prohibited e Deletion of the current or a lower level directory prohibited e No clever stuff like CURRENTDIR in the subdir name KD is a fairly safe program to use unless you start adding the switches to force it to skip the listing Now although I have this protection in KD while developing FLIT I had one or two nasty experiences because of the NUKE nature of count files BE WARNED I added one or two double checks on the calls but the biggest risk is that you ll ask it to select a directory which it never gets to but goes ahead and deletes
19. seen a notice of a package produced by the Institute of Electrical Engineers They have kindly sent me a complimentary copy well I have a couple of contacts I think I should warn you that it is only useful to those who need a rapidly outdating listing of articles books and compilers Unless you have experience of this kind of material you will be very disappointed The entire package is a single A4 booklet of less than 50 pages of material produced by a word processor that fully justifies text by inserting whole spaces Honesty forces me to query the utility of such packages when a continually updated package devoid of the glossy cover would prove to be far more useful APDCCWFSCFTAST A Public Domain C Compiler with full source code for the Atari ST Oh you lucky Atari ST owners a complete public domain C Compiler called Sozobon has just come the way of CUG It includes the full documented source for the compiler assembler optimiser and linker together with a library manager libraries everything includes the relevant source code and the most open Public Domain release note that you could want well you musn t sell it but you are positively encouraged to pass it on and develop it Of course it has its weaknesses There is some doubt about its handling of functions passed as pointers in parameter lists and its floating point routines are rather minimal no trig and double is only a synonym for float But every local group should have a co
20. sensible then coping with problems arising does not involve a complete rework of other modules Having said that there is no doubt that many functions go through an evolutionary stage where their return values or parameters are altered to suit changing situations Finally The functions available allow you to format any kind of DOS disk to read the type of disk or if one is inserted or to determine if the disk is an operating system disk This is the nitty gritty level I wanted to get to From here there a number of interesting ways to go but I rather suspect it s a bit too late to bother Copy protection has gone optical disks are not far off the day of the media ID byte has almost gone forever perhaps the next standard will be consistent in the way it uses things 28 Volume 1 Issue 5 The Source Library by Martin Houston What is it all about INTRODUCTION The CUG library is intended to be a collection of public domain C source code brought together so that anyone who wishes to may use the programs and further develop them both as an aid to their own learning and enjoyment and to improve the stock of C software in the Public Domain Very few real programs are ever written from scratch Most things are developed using and adapting parts from previous programs The library will serve as a toolkit of parts to aid in the process of developing new ideas May PD Software amp Shareware libraries carry some C source
21. stdin and stdout The MIT X Windows system is fast becoming the standard for graphical interfacing in the UNIX world Hardware I O For portability a program should never try to access memory or I O ports directly since the addresses of I O ports and system variables can change between different versions of the O S or the machine type IBM PC and PS 2 is a good example However most compilers provide some sort of port I O function inp and outp are common If it is really vital to access a specific memory location then a pointer can always be forced to a specific address declare a union of a long or short and a char but do so entirely at your own risk Neither the author nor the C Users Group U K can be held responsible for any damage Interrupts Traps amp Exceptions The signal function is about the only portable interrupt trap exception handler SIGINT usually corresponds to a user abort Ctrl C or Ctrl Break while SIGFPE can be used to catch floating point errors Proposed Standard For CUG U K Library Programs With the very wide range of machines and operating systems used by CUG members I would like to the following portability standard for use with programs submitted to the library The list is not intended to be exhaustive your suggestions and comments are welcome ED how about operating environments Windows PM Macintosh GEM X Operating System Dependencies fFdef UNIX Generic UNIX fdef ATT AT
22. the older people had done programming in other languages before One man was a real expert Our tutor gave a lecture on pointers for about half an hour In this half hour he also introduced us to more of the esoteric words arrays variables strings include printf etc He handed out copies of what seemed to be a fairly complicated programme and said that if we did not have anything already we should work through this programme There was a pile of books on one of the tables for consultation So we all went over to the computers and started It seemed that day that I had a question about practically every single word or symbol Francis our tutor gradually worked round the class giving helpful advice and suggestions so that we all in our turn could see our way to one or more steps forward This evening set the pattern for the weeks to come By the second class I had bought a book and I worked on one of the examples from it By now it was obvious that I needed a compiler of my own so that I could work at home Francis was very helpful in answering my questions about this and when I had bought one how to actually get it to work on my machine As the weeks went by I had an idea of what I wanted to create as a programme of my own I worked on this at home until I was stuck and on the class night I would set up the programme on the computer as far as it went and when Francis came round he would show me where I had typed it wrongly or make suggestions a
23. the whole concept of computing is something like a drug the more one has of it the more one realizes that there is so much more to know to find out about one is drawn onwards towards wider and ever more time consuming horizons Programming was one of these directions what was it that could make the computer respond with unbelievable alacrity or with considerable reluctance according to its whim to some arbitrary command I remember standing in front of the bookshelves at Harrods where the computer books are and looking at the introduction or back cover of every book that announced by its title that it touched upon the subject of programming I soon came to the conclusion that the C language was the thing of the future Whilst searching for some formal instruction in C I came across a C workshop for beginners and more experienced programmers which was shortly to start in the school opposite to where I live in Oxford After two terms and six or seven months later I can take stock of the methods employed and try to evaluate where I stand now and where I want to go I can remember that on the very first evening my impression that everyone engaged in the computer industry was either a Yuppie or a rogue or both was dispelled by the down to earth attitude and genuine helpfulness of everyone present There were a good number of young people 15 year olds seem to have a head and a half start upon people like me and it transpired that some of
24. to read the contents of whatever the pointer points to If you d like to see more or fewer articles like this then drop us a line at the usual address or I can be reached on CIX as philip Similarly if you dropped off half way through and would rather things went a bit quicker or conversely got lost after the first paragraph LET US KNOW Do bear in mind the old you can t please all of the people proverb I II go with the majority decision One Person s View by Francis Glassborow Francis Glassborow makes his debut in C Vu and gives out a few brick bats amongst the bouquets Sometime in the back end of last year I began to wonder if I had thrown my money away when I joined CUG Then a copy of C Vu dropped through my letter box As it had been such a long time since the previous issue I wondered if I had missed an issue I wrote to Martin Houston expressing some concern and at the same time offering a disc of C source code for the library The up shot of that letter was a phone call and eventually my attendance at the first AGM of CUG UK By the time you get to read this many months will have passed since your last issue of C Vu However you would be mistaken if you thought that CUG was slowly burying itself in inertia Though only a dozen members attended the AGM it was undoubtedly the most important event in the history of CUG A committee was formed which by now will have met twice and is already dramatically developing
25. KKKKKKKKKKKK File name lt name of this file gt x Program name lt name of program to which file belongs which as could be a library or an executable gt Source of file lt where the original came from before the library gt Purpose lt what it does gt 5 Changes lt who what when amp why major changes have been made gt x KK KK I KI I A A A IR OR KK RK KK lt disk num gt is the library disk number that the file comes from 0 means that the information has not been filled in The library will try to ensure that each file that goes out will have at least a blank header but it is largely up to the members to fill the headers in and keep them up to date I feel that this is a bit of discipline will be of great benefit to the CUG members as it will enable a database of what is in the software library to be kept so that answers can be supplied to such questions as Can you find me a function that does pattern matching or Are there any assemblers in the library as C source It will take a while before the library enquiries database is fully operational but I feel it is a goal well worth attaining The header will usualy only be put in the main module of any multi module program that obviously belongs together such as the xlisp sources If members want to go through and header each and every file then they are welcome to but doing so intelligently requires considerable knowledge of the structure of the program The
26. M MOVED Actually GEM enforces a couple of constraints on sizing First the window may not be sized off screen Second there is a minimum window size which is dependent on the window components specified when it was created This prevents features like scroll arrows from being squeezed into oblivion The most common application constraint on sizing is to snap the size to horizontal words as above and or vertical character lines In the latter case the vertical dimension of the output font is used with align Also be aware that the size message which you receive specifies the EXTERNAL dimensions of the window To assure an even size for the INTERNAL dimensions you must make a wind_calc call to compute them use align on the computed values back out the corresponding external dimensions with the reverse wind_calc and then make the wind _set call with this set of values A window resize will only cause a redraw request for the window if the size is being increased in at least one dimension This is satisfactory for most applications but if you must reshuffle the window after a size down you should send yourself a redraw as described above after you make the wind _set call This will guarantee that the display is updated correctly Also note that the sizing or movement of one window may cause redraw requests to be generated for other windows which are uncovered by the change The window full request with code WM_FULLED is actual
27. Volume 1 Issue 5 C Vu The Journal Of The C Users Group U K Mail 36 Whetstone Close Farquhar Road Birmingham B15 2QN Telephone 021 454 3448 Hi Welcome to Issue 5 of C Vu the Journal of the C Users Group U K This is also the fifth and last issue I shall be editing and maling up myself for a while at least Unless you re in the business yourself you ll be amazed at the amount of time it actually takes to get a half decent layout Anyway as from Issue 6 Martin Houston will be taking over the helm If you would like to take it over yourself I m sure Martin is open to offers We have been let down once already but if you are sure you can spare the time and obviously have the equipment I can flog you a second hand copy of Timeworks Desktop Publisher if you have an Atari ST then give Martin a ring on 021 454 3448 Right onto the interesting things Another good packed issue this time around hopefully something for everyone If there isn t then you know the cure either write it yourself or write to us telling us what you re looking for from C Vu we aren t telepathic I know we have already had quite a few new members since the last issue and te PC W Show in September should see another surge so I ll give a quick resume of the what the group is about At present the group has three main activities the one you re looking at which we currently publish quarterly although if we get sufficient material it c
28. al Cave adventure with full source code NEW 22 NEW 23a NEW 23b NEW 24a NEW 24b NEW 25a NEW 25b 42 Minx 2 Adrian Godwin has been busy again How to build C Kermit fixes amp library changes a C Kermit executable use dosread rename to kermit and chmod to 755 and a Minix more amp Is Languages 3 Small C Plus for the Z80 by Ron Yorston Volumes 23a and 23b must be ordered together See the article in this issue Languages 3 Small C Plus for the Z80 by Ron Yorston Volumes 23a and 23b must be ordered together See the article in this issue Comms 2 Sources for Kermit This is a FULL version suitable for a wide range of machines In particular it is suitable for MINIX Volumes 24a and 24b must be ordered together Comms 2 Sources for Kermit This is a FULL version suitable for a wide range of machines In particular it is suitable for MINIX Volumes 24a and 24b must be ordered together Comms 3 Docs for Kermit Essential to make full use of Kermit Volumes 25a and 25b must be ordered together Comms 3 Docs for Kermit Essential to make full use of Kermit Volumes 25a and 25b must be ordered together Volume 1 Issue 5 The C Users Group U K makes no representations or warranties with respect to the contents of The Source Library listing and specifically desclaims any implied warranties of merchantability or fitness for any particular purpo
29. alls The end of the rectangle list has been reached when both the width and height returned are zero Since some part of a window might be off screen unless you have clamped its position see below the retrieved rectangle is intersected with the desktop s area and then with the screen area for which a redraw was requested Now you have the particular area of the screen in which it is legal to draw Unless there is only one window in your application you will have to test the handle in the redraw request to figure out what to put in the rectangle Depending on the app you may be drawing an AES object tree or executing VDI calls or some combination of the two In the AES case the computed rectangle is used to specify the bounds of the objc_draw For VDI work the rectangle is used to set the clipping area before executing the eae Volume 1 Issue 5 VDI calls A SMALL CONFESSION At the beginning of this discussion I deliberately omitted one class of redraws those initiated by the application itself In some cases a part of the screen must be redrawn immediately to give feedback to the user following a keystroke button or mouse action In these cases the application could call do_redraw directly without waiting for a message The only time you can bypass do_redraw and draw without walking the rectangle list is when you can be sure that the target window is on top and that the figure being drawn is entirely contained within it
30. amp T specific UNIX def M XENIX Xenix auto defined by cc fFdef V7 Version 7 UNIX fdef SYS3 UNIX XENIX system III fdef SYS5 UNIX XENIX system V fdef BSD BSD specific UNIX Fdef BSD42 BSD Release 4 2 Fdef BSD43 BSD Release 4 3 fdef MSDOS Generic MS PC DOS fdef OS2 Generic OS 2 Fdef OS9 Generic OS 9 Fdef CPM for diehards H H H H H H H H H H H H H Hardware or Machine Dependencies ifdef AMIGA Commodore AMIGA series ifdef ATARIST ATARI ST series ifdef CRAY wishful thinking ifdef IBMPC Generic IBM PC amp Clones ifdef IBMPS2 Generic IBM PS 2 amp Clones ifdef SUN Generic SUN workstation ifdef APOLLO Generic Apollo workstation 11 Volume 1 Issue 5 CPU Type Dependencies fdef M I86 Intel i8086 family fdef M 1186 Intel 180186 Fdef M 1286 Intel 180286 fdef M 1386 Intel 180386 amp i80386SxX fdef MC68K Motorola 68000 family fdef SPARC Sun Microsystems SPARC fdef 280 Zilog 280 H H H H H H H UNIX is a registered trademark of AT amp T XENIX is a registered trademark of Microsoft Atari and Atari ST are trademarks of the Atari Corp OS 2 and PS 2 are registered trademarks of I B M Apologies for the use of any unacknowledged trademarks Professional GEM by Tim Oren Part Two more on windows EXCELSIOR In this installment we continue the exploration of GEM s window manager by finding out how to process the messages received by a
31. and then removed afterwards A flag passed to the function determines either initiation display or termination The function uses good protective programming in that it checks that it has been initialised correctly before doing a display This 26 Volume 1 Issue 5 function is also used to monitor the keyboard for an interrupt returning the appropriate status to the caller horiz_list Pass a window pointer and the list of choices the user can select from The cursor keys or the first letter is used and the function returns the index of the selected choice Service Level Functions Down at the service level there are a number of functions which will be useful for people talking to disks The thing to remember about the format functions is that they must be called in the correct order To format a track everything but everything has to be set up just right Volume Labels Two functions get vol label and set_vol_label allow you to do just that They work on DOS versions down to 2 so can be used safely with most disks They form a useful addition to your library Formatting To actually format a disk there are several things you have to look after These functions are contained in two modules FMTDOS C and FMTBIOS C Since we are almost down at the hardware level any thoughts of reuseability for these functions is abandoned We need to a Set up the BIOS Parameter Block to be a table of details that the BIOS can pass to the
32. ant Labtech Notebook Labwindows the inevitable Lotus products 123 Symphony Hal Measure and Manuscript MathCad Labview etc Language wise the group supports C in all its incarnations Forth QuickBasic and Assembler Finally on the hardware side products from Analog Devices BioData Hewlett Packard IBM National Instruments Siemens and TecMar all get a mention The main activities of the group are very much in line with ours a newsletter future articles are to cover everything from an introduction to C through transient capture and time series analysis to useful Lotus 123 macros and getting the most out of co processors local meetings public domain software applications and details of new and enchanced products Individual membership of the group is 14 00 p a corporate membership is 45 00 for up to five names and an extra 10 00 per additional name Added to each membership is a once only registration fee of 4 50 If you would like further details of the group just fill in the questionnaire included with this issue or write to them at P O Box 17 Retford Notts DN22 6BR Where readers write If you have a programming problem or can offer a solution to a problem mentioned here write to the Lettice Column Mr M D Cross Membership 8887 writes I have been trying for some time to obtain a copy of Microsoft Pascal V3 2 from commercial sources I would be grateful if any member can help with my quest
33. any library functions it needs we can execute it Depending upon the operating system being used it will either be executed from a fixed location in memory unusual or from wherever the OS can find sufficient contiguous free space to load the program into Naturally enough as well as the machine code that is actually executed the size of the program file includes space for any variables that you have declared So each variable will take up specific locations or addresses in memory How many locations they take up is a factor of their type In some implementations an int would take up two bytes a long four bytes and so on The details of this will or should be in your documentation If you type in compile and run the following program it will display the addresses of the variables count and increment together with the contents of those addresses SRY POINTEX1 C x fe aA Objective X7 o use of amp address of operator to find location in RAM of variable at run time ee Compiler Prospero C Ky Machine Atari ST Reference Articl The Dreaded Pointer Part 1 By Phil Stubbington x C Vu Volume 1 Issue 5 July 1989 es include lt stdio h gt include lt stdlib h gt include lt assert h gt void main int Count Increment assert sizeof long sizeof int Count 32 Increment 97 EN PN Using amp Address Of Operator To Find L
34. ar later Unfortunately there have been problems both at ANSI and between ANSI and It seems unlikely now that a C standard of any form will see the light of day before September There are also bad feelings in the UK at the lack of clarity in the standard it is not impossible that we will end up with different ANSI and ISO C standards If this happens C users will I guess vote with their feet The only consolation is that the final document is not likely to change much from the current draft If you are interested this can be obtained from the BSI Standards sales dept on 0908 221166 It is not particularly cheap at 30 pounds approx However the rationale which is in itself a very useful document is included I believe you can obtain it cheaper direct from ANSI in the States if you can be bothered with the hassle Special Interest C Groups I would also like to try and encourage some of you folk out there to get involved in some of the more interesting specialist C groups With this in mind the following article gives details of a numerical extensions group recently formed in the USA If anyone is interested in participating but does not have access to uucp or JANET email let me know and I may be able to arrange mail distribution from the UK Neil Martin British Standards Institute PO BOX 375 Milton Keynes MK 14 6LL Phone 0908 220908 x2813 Email neil bsiga uucp Telecom gold 84 MNU174 The Numerical C Extensions Group by Rex Jaes
35. arly with a few more casual attendees Gratifyingly most have already expressed the intention of joining again this Autumn The range of participants was very wide including the young teenage enthusiasts at one end to a retired enthusiast with over thirty years of programming experience For one member it was his first experience of using a computer for anything As it was a workshop not a course the range of experience and background only served as an advantage Technically I was in charge but very soon we had established a pleasant working atmosphere in which people were freely helping each other The willingness to help the novice is extremely important and needs to be nurtured if CUG is to avoid the fate of several other user sag Volume 1 Issue 5 groups that have become small cliques of experts At the end of this article collection of odds and ends I have included a piece written by one of the less experienced members of the workshop I think that the infectious enthusiasm of the young coupled with the expertise of the elder statesman has done much to ensure that Donald has enjoyed his monday evenings and is looking forward to continuing next year I hope this encourages some of you to plan the same sort of thing for your own area A Bibliography C Programming bibliography and information pack Paula D Fountain 1988 IEE P O Box 26 Hitchin Hertfordshire SG5 1SA Price 29 pounds Those of you who read Byte may have
36. art At The Bottom To begin with I wasn t sure whether writing my own format functions would be practical I started by unassembling the DOS FORMAT command and looking at the way it did things From version 3 onwards Microsoft use the IOCTL call handling the disk in a general purpose device oriented way IOCTL calls wrap the built in DOS and BIOS interrupts in a shell of control blocks headers and so on For my purposes this was too clever Simple format interrupt calls would do me I used DEBUG to examine the details of the BIOS Parameter Block and boot records of disks formatted by programs like PCTOOLS FORMAT and older versions of FORMAT By comparing this with the information available in books like the Norton guide and the technical reference manual I was able to determine exactly what had to be done I decided to proceed The Policy I try to avoid the use of global variables as much as possible since these often lead to difficulties in understanding when others have to work with your code It also restricts your ability to code and test modules in isolation There are times when they are more or less essential In general I have built modules relating to specific tasks Within these modules I create a set of private static variables to hold relevant information These variables may be changed by the use of posting functions or their current values be obtained through reporting functions This aligns with the ideas of object ori
37. at finding a good reference book including some specific to the Atari ST and GEM or even a training course should be no problem If your budget doesn t quite stretch that far you will also find a vast quantity of C source code in the public domain which is often of a very high quality and very useful for learning 46 Volume 1 Issue 5 about the language Overview Megamax Laser C MLC comes on three single sided disks with a 640 page paperback manual and costs 158 199 US The System disk contains all the programs you need to get things running although you will also need to copy the header files and run time library from the Works disk An addendum to the manual and details of how to convert your existing Megamax code to Laser C are also included The Works disk also contains the compiler controller cc and some example programs The Utility disk contains 16 tools utility programs plus the debugging library and its documentation After making backups of all the disks installation is simply a matter of creating a directory called MEGAMAX in the root directory and copying all the files and directories to it The Shell MLC is the only C development system that comes with a proper GEM based shell Metacomco provide a very rudimentary GEM shell Menu with Lattice C but it doesn t do much to speed up the programming cycle Other than that you are stuck with text based shells most of which attempt to emulate the shells
38. ation is also very good with plenty of examples which are often available on disk as well An improvement over previous versions and better than Mark Williams C apart from the few GEM routines that aren t documented Overall MLC is a good buy It is still the most compact C development system for the ST it can be comfortably run from just floppies and probably the fastest on compilation Megamax have also mentioned real technical support and a newsletter only time will tell Stop Press Since this review was written Megamax have released Version 2 0 of MLC The main difference seems to be support for a true source level debugger Laser DB An update on MLC will hopefully appear in a future issue of C Vu 50 Volume 1 Issue 5 Standard Watching by Neil Martin With Neil Martin of the British Standards Institute Hello Folks Let me introduce myself I am Neil Martin a senior software engineer with the British Standards Institute I am currently responsible for the setting up of a harmonised European Validation Service for C compilers and I am also a representative on the BSI C panel which is helping to produce the C standard I hope to try and keep the members of the user group up to date on the issues The ANSI and ISO Standards The whole business over the C standard is somewhat depressing It was expected that the ANSI version would be ratified and published early this year with the ISO version following about a ye
39. ber of messages generated would quickly fill up the application s message queue Finally note that every app MUST use this method even if it only uses a single window because there may be desk accessories with their own windows in the system at the same time If you do not use the rectangle lists you may overwrite an accessory s window INTO THE BITS First we should note that the message type for a redraw request is WM_ REDRAW which is stored in msg 0 the first location of the message returned by evnt_multi The window handle is stored in msg 3 These locations are the same for all of the message types being discuss The rectangle which needs to be redrawn is stored in msg 4 through msg 7 Now let s examine the sample redraw code in more detail The redraw loop is bracketed with mouse off and mouse on calls If you forget to do this the mouse pointer will be over written if it is within the window and the next movement of the mouse will leave a rectangular blotch on the screen as a piece of the old screen is incorrectly restored The other necessary step is to set the window update flag This prevents the menu manager from dropping a menu on top of the screen portion being redrawn You must release this flag at the end of the redraw or the you will be unable to use any menus afterwards The window rectangles are retrieved using a get first get next scheme which will be familiar if you have used the GEM DOS or PC DOS wildcard file c
40. bout changes which would advance it to its next stage By the end of the second term I had a working programme about three screensfull of C When run this asks 3 questions which if answered correctly each allows the operator to proceed to the next This has proved to be a never ending source of amusement to every visitor to our house most 44 Volume 1 Issue 5 of whom use computers at work and incidentally most of whom have never heard of C One other very noticable effect of the winter s work is that I now approach the task of operating my computer with much more confidance Some operations which earlier would have been a source of great difficulty can be performed precisely and quickly and with a far greater expectation of success When we recommence the class in the autumn I would like to work on a programme which would really be of use to me in my everyday work a spot of DIY programming if you like I think that I have some idea about what is possible and my work on the previous programmes has given me some clues on the ways I might go about it Scientific Magic Circle That s what the newly formed Scientific PC User Group aims to be a independent unbiased resource dispelling some of the myths and fears that surround scientists and engineers for locating help information and advice for scientists and engineers Most of the popular software and hardware products are supported including all versions of Asyst Asyst
41. chke Rex Jaeschke NCEG Convenor reports on the status of the group Reprinted with permission from The Journal of C Language Translation Volume 1 Number 1 June 1989 Copyright 1989 Rex Jaeschke 51 Volume 1 Issue 5 Introduction When I conjured up the idea for an ad hoc group to define numerical extensions to C earlier this year I had no idea as to what the reaction would be The evidence is now clear that this endeavour is seen as being very worthwhile Not only have more than 90 people asked to be added to the contact database but 30 of them attended the one and a half day meeting at Cray Research on May 10 11 The backgrounds of the attendees was diverse The supercomputing industry was represented via Cray Convex Supercomputer Systems and Thinking Machines The IEEE community was well represented by Hough from Sun Cody from Argonne Labs and Thomas from Apple Other organizations represented included Unisys Microsoft Main Numerical Issues Digital Equipment Corporation H P CDC IBM Solborne pau A Farance Inc University of Minnesota Inter metrics and vectorization 27 Information and Graphics Systems The digital signal complex 27 processing industry was represented by Analog Devices and l LLNL Army BRL and Polaroid Corporation represented the Y iably dim arrays 25 user community Dennis Ritchie from AT amp T also participated IEEE issues 24 There was no real sentiment that we d
42. copy them over it took 6 hours to do the lot The Manuals The four manuals supplied include User s Guide and Mixed Language Programming Guide Language Reference Microsoft CodeView Microsoft Editor and Utilities guide a Run Time Library Reference and the Quick C Programmer s Guide The quick reference guide is thicker than the one supplied with version 4 0 and lists all command line options for the compiler debugger and other utilities and a brief synopsis of all library functions It is ring bound and has a stiff cover so it could easily be persuaded to stand up next to your computer The Quick C manual is a bound paperback 400 pages long Most of the manual leans more towards the beginner to C than the other three and contains chapters introducing the C language These 4 Volume 1 Issue 5 chapters however are very brief and are more suitable for an experienced programmer coming from another language than for someone just learning to program Other chapters describe the graphics library the Quick C environment and the other tools on the disks however no run time library guide is included The other manuals are much the same as those supplied with version 5 0 except that the binders have been made larger to accommodate the extra information If you paid for the cheap upgrade from version 5 0 then you won t get the new binders you ll have to squeeze the extra pages into your old ones Whether you pay the full price or
43. d make utility The latest version 2 0 has a good hypertext like help system but the one supplied with our compiler version 1 03 isn t all that bad Highlighting a function name in your source code and selecting help brings up a window that shows the function prototype and the name of the include file in which it is defined The product is the largest single program supplied in the package It is over 300k in size 326k to be exact and requires at least 512k memory to run in It doesn t use expanded memory so be prepared to have to shove out a few TSRs to get it to fit in And another thing don t even consider running it from a dual floppy machine It takes practically a lifetime to load The editor emulates WordStar up to a point The user manual doesn t list all the keystrokes and the on line help only lists a few You can have two files in memory at once but when switching between them the program prompts whether you want to save the active file to disk You can 7 Volume 1 Issue 5 disable the prompt but not the writing to disk I used Quick C to develop a project comprising several C source code files but I soon had to switch back to Brief and the command line compiler when I began running out of memory Quick C is good for quick prototyping or small programs but anything larger just won t fit Furthermore assembler modules are not handled and not all library functions are available in Quick C If you need the missing functio
44. disk controller IC b Set up DOS so that it knows all the details about the disk number of sides sectors tracks etc c Prepare an image of address markers that will be written to the disk used later for seeking to a given location d Step through each track with a format amp verify call to BIOS e Build a File Allocation Table with a note of any bad tracks f Write the boot record and the system tracks to the disk Who Knows What Notice that DOS doesn t know much about formatting of disks it assumes that the address marks are available for it to manipulate files using the directory entries and the FAT DOS has two functions absolute read and absolute write to allow you to talk to disks in a sort of raw mode In this case I had no use for the read function but the write one might have been useful the only thing is I hate seeing the Abort Retry Ignore message thus necessitating writing my own absolute write function This converts DOS sector number system to BIOS sector numbers and returns a code indicating success or failure 297 Volume 1 Issue 5 Functions in Use To use the format functions you first call disk _set with the media type and the drive number This sets up the parameters for DOS set_disk_info and BIOS set_bpb_ data converting our high level name of the media to the number of sectors system information and so on disk_set also performs any calls required to configure AT machines for the media s
45. e link and run it The entire process is carried out by topping the source window and pressing Control R Additionally it will only compile those files where the source code has been altered since the last link This facility is really a simplified version of the make tool described later on You can also specify which files are to be compiled and linked the name of the final program and if you want a symbol table generated which you will when debugging This information can be saved to disk if required 47 Volume 1 Issue 5 Debugging programs is a pain at the best of times but fortunately the Laser shell eases the process When your program crashes control normally returns to the shell and the STDIO standard input output window will show exactly where you crashed Additionally pressing Control Delete will stop any program in its tracks even GEM based programs which otherwise would require a quick tap of the reset button There isn t really much you can say about RAM residency and RAM cache apart from the fact that they work and that they speed things up tremendously It would have been nice though if Megamax had given details of the file format for RAM resident tools so that you could add your own Finally the Laser shell allows you to run HES mu oN LJ most text based programs in the STDIO EEE i 1 Cire o 9 window as long as they don t use any attributes Wrote Thea es CT J nae fancy control codes I fou
46. e and several other enhancements Languages 1 language compilers and interpreters in C Thus volume contains sources for XLISP the object orientated version of the lisp programming language Math a comprehensive collection of the usual functions Also contains a set of MASM macros for the 8087 co processor programs for numerical integration and matrix manipulation Unix Utilities 1 pattern matching language make project management tool stream editor complete with example sript convert Pascal to C and several minor utilities Unix Utilities 2 text processing and printing a couple of text formatters entabbers and detabbers menu driven setup programs for IBM and Epson printers 3 12 13 14 41 Shells two Unix style single tasking only though shells for MS DOS source code included so conversion to the ST amp beyond is a possibility why not give it a try C Language Tutorial 1 this disk contains the text of the tutorial Most of the example programs can be found on volume 10 C Language Tutorial 2 the example programs to accompany the text found on volume 9 Comms 1 several comms protocols Kermit SEAlink and library managers Arc Lump Squeeze and some related utilities PC Utilities 1 some of which are provided as executables only Contains an extensive shareware window manager cursor control progs from Bill S
47. e intent is that the real technical work will go on between meetings and be coordinated by the leaders of each subgroup Then at the following meeting each subgroup will present the results of its work and make formal proposals as appropriate This way the committee can focus on the final distilled issues rather than everyone getting involved at all levels It will also significantly reduce the amount of paper in the mailings If you wish to participate in any of these subgroups it is your responsibility to contact the leaders and identify yourself your concerns and how you can help If your area of interest is not listed here start your own subgroup and let me know Mailings and Submissions Most of people interested in NCEG appear to have an e mail address so that should 52 Volume 1 Issue 5 make the subgroups job much easier in coordinating various viewpoints and proposals However all formal distributions will be by paper mail Since meetings are to be once every six months there will be two mailings between meetings The first will occur within 4 6 weeks after a meeting and will contain minutes new papers and other appropriate correspondence The second will occur about 4 6 weeks prior to the following meeting The cut off date for formal submissions for the September meeting is August 11 Forward all correspondence to me either by mail or via uunet aussie rex and I will assign it a document number Note that I do not have a trof
48. e way I suppose a version of FLIT will be available in the club library To anyone who has ever thought about getting down into the nitty gritty of the DOS BIOS disk level my advice is DON T Not unless you really have to It s not so much that it s difficult it s just that there is a limited amount of information around and much of it is unclear or contradictory As a result a great deal of experimenting is required My hat goes off to the guys in companies like Central Point Software MACE and so on To get the level of knowledge these people have must take years With me this sort of thing is almost a side issue The timescales are in years but the knowledge level is a lot less At the application level FLIT uses a library of window functions to handle the user interface This is available in the source library if anyone wants to play around with it What the user sees is a menu of choices allowing him to set up the number and type of disks he is copying FLIT looks after temporary storage areas and prompts for the disks as required Essential to me was the need to only ever have to insert a disk ONCE regardless of its size and the number of copies being made FLIT tries to be sensible as you would about compressing several smaller sized disks onto larger ones It will format disks if asked or if it feels it s necessary Sounds simple and in the end the program is less than 80k bytes LI Volume 1 Issue 5 Where Do You St
49. eliberately go against the exceptions errno 24 direction established by ANSI C In fact quite the contrary However it was recognised that some of ANSI C s constraints float long double library 23 may impede our activities resulting in possible conflicts The parallelization 22 whole issue of errno and formatted I O of NaNs and infinity are examples ANSI lt math h gt 21 array syntax 19 The Issues extra math functions 17 The main purpose of the meeting was to identify and prioritise aggregate initializers 15 the principal technical issues The group then voted on each inter language issues 15 topic indicating high or medium or no priority The high priority votes were weighed twice as much as the medium and wide accumulators 10 a list of priorities resulted inset math function precision 9 Another topic Arrays as first class objects had a high priority non zero based arrays 8 21 but after considerable debate was dropped from the list i 3 pe numerical representation 6 since it was agreed its addition would likely cause great confusion to existing C programmers Formation of new data types 4 Subgroups The bulk of the agenda time was then given to the pew operators 4 top ten topics each getting 20 30 minutes For each of these l topics attendees volunteered to be the primary and alternate function overloading 4 co ordinator The minutes of the first meeting identify these people In the interim contact me for details Th
50. en they don t have to be there Thus we could have a function which will display an alarm message and sound the bell annunciate BELL Out of range which we could call like this annunciate CLR MESSAGE Both of these work because the first parameter is a control According to its value the function will or will not expect further parameters Since none are required to clear the message we need only pass the control itself Furthermore if we decided to add a complexity to our function which required further parameters to be passed then we rewrite the function to only check for these further parameters if the control requires it We do not need to change any of the existing programs which call this function Note that LINT and similar systems may observe the fact that a function is called with differing numbers of arguments it is however perfectly acceptable C Rather than passing a separate parameter to a function another method is to set the data to some invalid or out of range value e g e 1 asa flag in a series of positive data e an empty string for a message function e NULL to a function expecting a pointer However whilst these methods do have a place I do not feel they are suited to selecting options within a function nor are they suitable for choosing different paths NULL pointers can be a valuable way of detecting error conditions and that brings us to the next topic The
51. ented programming we pass messages to objects modules in this case and ask them to do something for us In many ways this makes the code easier to read with the right choice of variable names and allows modules to be easily tested in isolation It is a reflection of the success of this method that most of the modules were tested with a very few lines of stub code getting them to a high level of completion before linking them into the final application Engine 1 remove a directory count_files The directory removal function would form part of a useful stand alone utility KD KillDir I decided to start here The resulting function count_files actually performs two roles hence the title Given the name of a directory including drive it will either return the number of files in that directory and all subdirectories optionally listing or deleting them as it goes Now the subdirectory structure leads one to think that a recursive function would be suitable here and in fact count_files IS recursive However we have to be careful What we want is for DOS to name all the files for us and then if a subdirectory is encountered perform a recursive call Fact DOS is not re entrant so when we use its directory search interrupt we must finish and be done with one directory before we can use the same interrupt call as part of any recursive C function on a further subdirectory Since we have no knowledge of the order of f
52. everything anyway Engine 2 fast file copy fast_copy The fast copying function is fairly straightforward it s necessary to use the DOS calls to get all the details about the file so we can exactly clone all its attributes Microsoft C makes this rather easy since they provide a set of DOS interface calls For other compilers the use of the int style call or asm directive may be required To make things as fast but as flexible as possible I have fastcopy try to grab the biggest buffer it can gradually shrinking this until it gets too small to do anything Fastcopy returns an error code according to any problems it s had and copydir The directory copying function of course calls the fastcopy function to do the work Copydir accepts the name of a source and target directory and clones one from the other almost It returns an error code according to it s success or otherwise DOS does not really allow us to create new directories with a date other than the current one So the date tagging on copied directories will not be the same as the original Does it matter The only way I can see to do this easily is to change the date time call the the mkdir function and then change the date time back This is not a nice thing to do Also it does not handle the fact that each level actually has it s own date amp time tag I could have changed the methods to handle this problem but decided it was a fair compromise
53. f formatter However do that only if your paper is concerned with issues other than those being handled by the subgroups For subgroup issues forward papers to the subgroup coordinators so they can include it in their submissions to me The intent is to avoid excessive duplication of points and to allow the short meeting time to be used more effectively The more formal documents we have the slower it will go Tom MacDonald at Cray Research has agreed to do the mailings at least for the interim Frank Farance of Farance Inc has volunteered to be the redactor of the group s working document Thanks to Tom and Frank Thanks also to Randy Meyers from DEC who acted as meeting secretary and to Cray for being meeting host Formal Affiliation There was general consensus that we become affiliated with a recognized standards organization The final proposal was that we become a working group within X3J11 If we follow that route it will result in our publishing a Technical Report a non binding report on our findings and recommendations With suitable planning we might be able to have that elevated to a Technical Bulletin and get it distributed with the ANSI Standard Getting our extensions adopted as a standard is also possible in the long term At this stage I plan to ask for agenda time at the next X3J11 meeting to discuss admitting us as a work group In the interest of economy the next two meetings are scheduled in the same location and week as t
54. fferent types of computer from 8 bit microcomputers up to super computers such as the Cray family so a program particularly public domain programs may end up running on a totally different machine to the one for which it was originally written Data Types While sizeof will return the number of bytes in a particular data type care should be taken to avoid assumptions about the actual size of a particular type Normally a char occupies 1 byte a short 2 bytes and a long 4 bytes These are the only assumptions that can be made with any degree of safety An int is not included in this list because the size varies on an Intel 8086 based system it occupies 2 bytes whereas on a Motorola 68000 based system it occupies 4 bytes To confuse matters further an int is 4 bytes on an Intel 80386 in native mode If binary data interchange is required between systems attention must be paid to structure packing mentioned in part 1 and to byte and word ordering CPU Short Long a0 al a0 al a2 a3 PDP 11 b0 b1 b2 b3 b0 b1 VAX 11 b0 bl b0 b1 b2 b3 180x86 b0 bl b0 b1 b2 b3 680x0 b1 bO b3 b2 b1 b0 Byte ordering for short and long types UNIX uses PDP 11 ordering as the reference point so VAXes and Intel chips are WORDSWAPPED while a 680x0 is BYTESWAPPED Operating Systems A program will normally use the operating system for file operations and process control In general the operating system of a computer is hidden behind t
55. found on Unix systems ie cryptic commands usually limited to two characters and a total lack of integration Whatever size of program you are writing most time is usually spent going round in circles edit compile link find bugs edit compile and so on As each of these stages would typically involve loading a separate program from disk anything that can be done to speed up the process has got to be a good thing The Laser shell attacks this problem in three ways e the editor is integrated into the shell e any of the programs eg compiler linker provided with MLC can be made RAM resident This removes the time consuming transfer from disk including RAM disks to memory and e frequently used files typically the source and object code of your program are held in a variable size RAM cache After the Laser shell is launched and the RAM resident tools are loaded you are presented with the usual GEM menu bar and desk top All the usual file management routines copy move delete rename etc are built into the shell and are available as separate tools Unlike current versions of GEM Desktop and most of the text based shells copying files doesn t require endless disk swapping if you are stuck with a single drive Strangely the Laser shell has no routine for formatting disks although the source code for such a program is included on the Works disk Once you have typed in your program the next stage is to compil
56. he run time library but differences will always occur mostly in the file naming conventions For example a file could have a full path name under UNIX of usr ronw lib filename for MSDOS it could be c usr ronw lib filename or c usr ronw lib filename in any mix of upper or lower case while under VMS it could be SYS SYSTEM USR RONW LIB FILE NAME Volume 1 Issue 5 High Level I O The high level functions fopen fclose fread fwrite fprintf etc are the most portable of the file i o functions The only differences normally occur on the modes for fopen but r read w write and a append should work without problems Low Level I O The standard low level functions open close read write amp lseek are direct usually direct implementations of the UNIX system calls to perform these functions The only problems usually occur with the open function To avoid problems do not use numbers for the open mode or create mode arguments instead use the defined constants Text or Binary Mode This problem DOES NOT occur under UNIX but does occur under MSDOS and some other operating systems The problem is due to the method the operating system uses to mark a new line n in files UNIX uses the ASCII line feed character while MSDOS us es a carriage return line feed pair In text mode a cr If pair will be translated to a single If when reading from a file and a If will be translated to a cr If pair when writing a file
57. hose of ANSI Cs X3J11 These NCEG meeting dates are September 19 20 Salt Lake City Utah and March 7 8 1990 New York City Let me know if you want a sample issue of the Journal of C Language Translation If so provide your mailing address Contacts If you would like to get in touch with Rex Jaeschke he can be contacted at The Journal Of C Language Translation 1810 Michael Faraday Drive Suite 101 Reston Virginia 22090 USA For any readers on the other side of the pond or with limitless pockets telephone 703 860 0091 53 Volume 1 Issue 5 Copyright amp Things All material in C Vu is C Copyright 1988 C Users Group U K or of the individual authors and may not be reproduced in whole or in part without the written consent thereof Any article in C Vu is published in good faith on the understanding that the author has all rights over it and that the C Users Group U K has the right to publish it We cannot of course prevent you from offering that same article to other publications but please let us know if the article has been accepted on an all rights basis Where the C Users Group U K is approached by publishers wishing to reprint articles the author will be informed but the group cannot take any responsibility for any agreements reached between author and publisher To put it another way if you get messed around don t blame us C Vu is composed entirely on an Atari 1040STF using an Atari SH205 a
58. ich is not on top or if the currently topped window is closed by its application or desk accessory Normally the ee Volume 1 Issue 5 application should respond to this message with wind set wh WF TOP 0 0 and allow the process to complete In a few instances a window may be used in an output only mode such as a status display with at least one other window present for input In this case a WM_TOPPED message for the status window may be ignored In all other cases you must handle the WM_TOPPED message even if your application has only one window Invocation of a desk accessory could always place another window on top If you fail to do so subsequent redraws for your window may not be processed correctly WINDOW SLIDER MESSAGES If you specify all of the slider bar parts for your window you may receive up to five different message types for each of the two sets of sliders To simplify things a little I will discuss everything in terms of the vertical right hand side sliders If you are also using the horizontal sliders the same techniques will work just use the alternate mnemonics The WM_VSLID message indicates that the user has dragged the slider bar within its box indicating a new relative position within the document Along with the window handle this message includes the relative position between 1 and 1000 in msg 4 Recall from last column s discussion that this interval corresponds to the freedom of movement
59. ideas for the future of CUG As from September the ordinary member should begin to notice a steady increase in activity On the other hand you the members should expect to increase your own activities About now you may be wondering why I am writing this That s difficult to explain as I am only a simple committee member and not one of the officers But I think that promises of changes and goodies to come might be better reported by an erst while ordinary member who has had his moments of doubt In the rest of this article I will describe a few of the things that I know about and hope you will wish to support actively for preference The PC Show ex PCW Show You know the one that used to be called The PCW Show We are going to be there this year and if nao ae Volume 1 Issue 5 you are coming please help in the following ways 1 Find our stand in the ACC section when you first arrive and introduce yourself 2 Collect and wear a badge declaring your CUG allegiance so that others will see that we are alive and healthy 3 Volunteer to help on the stand even if it is only for half an hour 4 Come to the daily meets that we will be arranging It is your committee s opinion that we should be doing everything possible to increase the amount of dialog and social intercourse between C Users The PC Show activity is only a small part of this Local User Groups Up until now the only form of membership of CUG has been for individuals As
60. iew is the facility to view structures The debugger recognises nested structures so moving the cursor to the name of a nested structure and pressing the RETURN key opens up another window showing the contents of that structure You can use this feature to walk through a linked list without needing to deal with memory dumps The same command works for structures in BASIC Pascal and MASM The protected mode version of CodeView runs under OS 2 and allows debugging of separate threads You can run threads at full speed switch between threads or freeze background threads while others run at their normal speed Microsoft Editor The new Microsoft Editor is something of a disappointment in comparision It is a fully programmable editor which allows users to extend it s facilities by writing extension programs in C and loading them when the editor is started However the editor is fairly awkward to use in comparision with Brief my standard editor and hints somewhat at an EMACS ancestry The editor insists on writing modified files back to disk each time that you switch buffers and there is no way to exit the editor without having it write back out all files which have been modified You can set an internal switch to change this behaviour but details on how to do this is buried somewhere in an obscure place at the back of the manual The editor can be configured to emulate other editors Files to emulate Brief Epsilon and the WordStar Quick C keyboard
61. iles and directories on a disk we have to assume that 22 Volume 1 Issue 5 we may be looking at a situation like this Filel File2 SubdirA filea File3 fileb SubdirB SubdirX In other words files and subdirectories appear in any order This involves actually performing two scans of the directory at each level One to locate the subdirectories and save their names then another to perform the action on each subdir The action calls may be recursive since we no longer have to hold over a DOS interrupt into a recursive C function call The pseudo code is If nesting level too deep then exit while a file or subdir exists skip self and parent form wild card search pattern if deleting read only files change attributes if deleting delete all files in directory if talking name the files while any subdirs save subdir name for each subdir form new subdir name recursive call if removing directory remove directory remove current dir return number of files counted I put a check on the nesting depth because things can get out of hand if you re not careful In real life not many people go down to the 32 levels or so possible with DOS so I felt a restriction here was fair It avoids the stack getting full since we need to grab quite a chunk from the stack each time Notice that the function to remove the files do_deldir uses the old style FCB call and not the new handle call The
62. implemented on a wide range of systems including the Atari ST and Commodore Amiga Prior to this announcement the only C compiler available under Mirage was the singularly unexciting Lattice C V3 03 In addition to C a wide variety of languages including Fortran Pascal Lisp BASIC and Assembler are available Swifte C looks set to live up the extremely high standard set by previous in house developments Feature wise the compiler is fully K amp R compatible and Swifte have pledged support for the ANSI standard In keeping with their previous language products Swifte C and subsequent code is said to be compact fast and re entrant Swifte C supports the 68020 and 68881 and no limitations are 3a Volume 1 Issue 5 imposed on code or data size For further details contact Francis Cox on 01 922 8850 or at Sahara Software Ltd South Bank Technopark 90 London Road London SE1 6LN Turbo C For The Atari ST Although rumoured for some time the appearance of Turbo C must rate as one of the most unexpected products of all time Details are still quite sketchy but the compiler is said to be fast and well optimised Floating point routines are nothing to shout about and the manual and on line help are in German an English translation will probably be available by the time you read this Rumour has it that Calamus the heavy weight DTP package was written using Turbo C so it is obviously quite a solid product and who needs floating poi
63. in the portion of the window which is exposed on the screen It is the job of the 12 Volume 1 Issue 5 application to determine in what portion of the rectangle it may safely draw This is done by examining the rectangle list associated with the window A rectangle list is maintained by GEM for each active window It contains the portions of the window s interior which are exposed i e topmost on the screen and within which the app may draw Let s consider an example to make this clear Suppose an app has opened two windows and there are no desk accessory windows open The window which is topmost will always have only one rectangle in its list If the two are separate on the screen then the second window will also have one rectangle If they overlap then the top window will break the rectangle of the bottom one If the overlap is at a corner two rectangles will be generated for the bottom window If the overlap is on a side only then three rectangles are required to cover the exposed portion of the bottom window Finally if the first window is entirely within the second it requires four rectangles in the list to tile the second window Try working out a few rectangle examples with pencil and paper to get the feel of it You will see that the possible combinations with more than two windows are enormous This by the way is the reason that GEM does not send one message for each rectangle on the list With multiple windows the num
64. inside story Having decided on the data type being passed to a function a few general points can be made about handling it Validity There will almost certainly be some checks you can perform on the received data The only reason you might not perform these checks is that of performance speed This will normally only be an issue in low level functions which can be excused for not carrying out full validity checks In medium to high level functions every opportunity should be taken to test for e presence of data e range limits Exit data too e valid options specified e required globals present initialised e prior process steps required completed OK 19 Volume 1 Issue 5 e error flags clear All checks wouldn t necessarily be included in all cases The programmer must decide which to include If you ask why you should include any when it s only you that s going to be using the function then the answer is that YOU make mistakes An untrapped error may ripple through a program causing strange sometimes invisible errors in routines far removed If a function is to be used by others and you don t put in proper error checking then it s like giving someone a cup of tea with a hole in the bottom of the cup If data appears not to have limits or none have been specified then you should feel free to apply some A limit which is far removed from the normal working range yet still allows the function to operate correctly should
65. is no means of examining any memory location unless a pointer happens to be pointing to it As a serious development system Quick C is very limited though I understand that the latest version corrects most of these deficiencies The Cost If you already own version 5 0 you can upgrade cheaply to the latest version through Microsoft UK If you purchased version 5 0 before 1st March 1988 the cost is 57 50 including VAT If you purchased after that date then the upgrade is free Owners of earlier versions of the compiler can upgrade for only 109 50 including VAT Otherwise you pay 275 00 for the full package When upgrading you will need to return your old master diskettes as proof of purchase For upgrades contact Microsoft UK at Excel House 49 De Montfort Road Reading Berkshire RGI 8LP telephone 0734 500741 telex 847924 Microe G facsimile 0734 507624 Conclusions The product is not without its weak points For me these are the Quick C environment and the Microsoft Editor but I suspect that other people may find these products more useful than I did The compiler itself is fast generates very compact code and provides a whole range of features and options For the cost it represents a truly professional package and is unreservedly recommended Volume 1 Issue 5 Writing Portable C Programs by Ron Wellsted Part II The Run Time Environment Since the C language has been implemented on many if not most di
66. ize INT17H call and determines if the disk is formatted via the is_formatted call Finally we determine if the disk is a system disk DOS files in the first two directory locations by performing the is_system call If it is a system disk is _system will have read the boot record which can now be posted to the system management module for safe keeping is formatted may be used after calling disk_set to determine the format of any disk It returns a numeric code according to whether the disk is formatted to the size we expect whether it s blank and whether it s write protected Time to Develop Developing the actual format engine did not take as long as I though it might It s broken down into sensible chunks and it s generally possible to test each one individually Getting the algorithms right to work out the cluster entry in the FAT and to convert DOS sector numbering to BIOS numbering took a bit of playing with After that the judicious use of DEBUG to read back what s actually been written to the disk did the rest Even once the format engine was complete and the user interface was clearly defined I still spent quite some time making sure that all possible problems were handled in a sensible way This is often the area that gets missed in functional specs since very often it is not clear what the impact of fault conditions will be until the system is actually running Hopefully if the original methods and structuring are
67. l continue to redraw this tree with no intervention on your part Obviously the new definition must be carefully built to fit the desktop area exactly or garbage will be left around the edges For the truly sophisticated a user defined object could be used in this tree with the result that your application s code would be entered from the AES whenever the desktop was redrawn This would allow you to put VDI pictures or complex images onto the SIT Volume 1 Issue 5 desktop background A SIN OF OMISSION In the last column I neglected to mention that strings whose addresses are passed in the WF_NAME and WF _INFO wind set calls must be allocated in a static data area Since the AES remembers the addresses not the characters a disaster may result if the storage has been reused when the window manager next attempts to draw the window title area COMING SOON This concludes our tour of GEM s basic window management techniques There have been some unavoidable glimpses of paths not yet taken forward references but we will return in time On our next excursion we will take a look at techniques for handling simple dialog boxes and start exploring the mysteries of resources and object trees Structure Part 5 by Colin Masterson What makes a good procedure We have spent some time discussing the basics of structured programs and shown that a good data type can be a help We now go on to consider what makes a good procedure
68. ling a function tell_copydir as we copy each file This passes the name of the file we are copying and returns true or false depending on whether copydir should continue or not This is fairly satisfactory if we re using copydir in a situation where we don t need the interim reporting we can just code tell_copydir as a single return TRUE statement In FLIT tell_copydir is quite sophisticated itself calling other functions to gather the information it needs to paint a full picture of the current status A Continuing Struggle This same problem arises during formatting the need to give some application feedback as to what s going on from a very low level machine dependent function There is a constant battle here to preserve the structured nature of our code whilst allowing user interruption and providing user feedback There is another way of handling this sort of problem which requires us to re think the way we conceived the original task If you recall we saw it as a loop copying all the files until it was complete We could also consider it as a function which copied the next file in it s list each time it was called When one file is done it returns a code reporting progress Now we still have to surround this function with a loop of some sort the difference is that this loop is at the application level and therefore has knowledge of the user interface Before our loop was at a low level with no knowledge of the user in
69. lly drives me nuts is having to sit at a machine waiting to open and close drive doors as I m copying disks I had a dream I dreamed of a program that would make my life a bit easier I probed the public domain libraries tested the tools scanned the software and looked at lists but couldn t find anything to do what I wanted That was the main reason for starting FLIT I also had an interest in getting to know a bit more of the detail of the DOS BIOS disk handling with a view to introducing some simple copy protection onto my own disks 20 Volume 1 Issue 5 The Concept The original concept was simple Most machines have hard disks these days all I needed was a program to e create a temporary directory on a hard disk e copy files into it e copy them off onto another disk and e remove the temporary directory This immediately revealed the need for a number of key engines within the program These were e A disk format function e A fast disk copying function which would exactly clone every detail of a file e A directory copying function which would copy a complete directory and all subdirectories e A formatting function e A directory removal function to delete a complete directory leg The Plan Like all good plans I decided to take things in stages Of course things turned out to be a bit more complicated than I had originally imagined However I think I m there now and I ve built some interesting functions along th
70. ly a toggle If the window is already at its full size as specified in the wind create then this is a request to shrink to its previous size If the window is currently small then the request is to grow to full size Since the AES records the current previous and maximum window size you can use wind _ get calls to determine which situation pertains The hndl_ full utility in the down load modified from Doodle shows how to do this The zoom box effects when changing size are optional and can be removed to speed things up Again if the window s size is decreasing no redraw is generated so you must send yourself one if necessary You should not have to perform any constraint or snap operations here since presumably the full and previous sizes have had these checks applied to them already The WM_CLOSED message is received when the close box is clicked What action you perform depends on the application If you want to remove the window use wind _ close as described in the last column In many applications however the close message may indicate that a file is to be saved or a directory or editing level is to be closed In these cases the message is used to trigger this action before or instead of the wind close Folders on the Desktop are an example of this situation The WM_TOPPED message indicates that the AES wants to bring the indicated window to the top and make it active This happens if the user clicks within a window wh
71. making your programs language independent any text such as error messages should be in the resource file rather than the program itself Essential for sane GEM programming but this implementation is incomplete ignores any alerts in a resource file Buy K Resource or WERCS instead Documentation The main documentation for Laser C is a 640 page paperback which is perfectly readable and indexed for a reference book Additionally there is an addendum and documentation for the debugging library on disk The paperback contains a tutorial details of the various programs and 49 Volume 1 Issue 5 functions provided and several appendices Each function or function group starts on a new page and starts with a brief synopsis of the function and any parameters passed to it This is followed by a paragraph or so of description and a brief example or program extract Strangely although the actual library contains bindings for every GEM call the manual doesn t document some of the less commonly used routines at all On The Bench MLC certainly felt like the fastest C development system but just in case my eyes were deceiving me I carried out some simple tests Using my Show GEM demonstration program around 800 lines I timed how long it took from invoking cc to seeing the opening alert box With autosave off and files in the cache this took 18 seconds Using Mark Williams C Version 3 0 5 the equivalent operation took 56
72. n Now let s look at each window control request in detail The message code for a window move is WM MOVED If you are willing to accept any such request just do wind set wh WF CXYWH msg 4 msg 5 msg 6 msg 7 Remember that wh the window handle is always in msg 3 The AES will not request a redraw of the window following this call unless the window is being moved from a location which is partially off screen Instead it will do a blit raster copy of the window and its contents to the new location without intervention by the app There are two constraints which you may often wish to apply to the user s move request The first is to force the new location to lie entirely within the desktop rather than partially off screen You can do this with the rc_constrain utility by executing re_constrain amp full amp msg 4 14 Volume 1 Issue 5 before making the wind _set call Full is assumed to contain the desktop dimensions The second common constraint is to snap the x dimension location of the new location to a word boundary This operation will speed up GEM s blit because no shifting or masking will need to be done when moving the window To perform this operation use align before the wind_ set call msg 4 align msg 4 16 The message code for a window size request is WM_SIZED Again if you are willing to accept any request you can just turn it around with the same wind set call as given for W
73. n application when it has a window defined on the screen Also beginning with this column sample C code demonstrating the techniques discussed will be available on SIG ATARI in DLS This will allow you to download the code without interference by the CIS text formatter used by ANTIC ONLINE output The file for this column is GEMCL2 XMO All references to non GEM routines in this column refer to this file Please note that these files will not contain entire programs Instead they consist of small pieces of utility code which you may copy and modify in your own programs REDRAWING WINDOWS One of the most misunderstood parts of GEM is the correct method for drawing within a window Most requests for redrawing are generated by the GEM system and arrive as messages read with evnt_multi which contain the handle of the window and the screen rectangle which is dirty and needs to be redrawn Screen areas may become dirty as a result of windows being closed sized down or moved thus exposing an area underneath The completion of a dialog or closing of a desk accessory may also free up a screen area which needs to be redrawn When GEM detects the presence of a dirty rectangle it checks its list of open windows and sends the application a redraw message for each of its windows which intersects the dirty area CAVEAT EMPTOR GEM does not clip the rectangle which it sends to the application that is the rectangle may not lie entirely with
74. nd the disk version is created using just about any and every text editor you care to mention STedi MicroEMACS ST Writer Elite Turd Perfect etc etc ISSUE 6 DEADLINE All material for issue 5 should be submitted by Ist September 1989 Any material submitted after this date is unlikely to appear in Issue 6 Please please please include a draft printed copy of any articles along with the text file on disk Remember to include your name title and or curriculum vitae in the article If you have any queries about the group contact Martin Houston at 36 Whetstone Close Farquhar Road Birmingham B15 2QN Telephone 021 454 3448 Alternatively leave a message in the c_users_group conference on CIX or mail to mwhouston pr philip 54
75. nd this useful when using the egrep tool to generate a cross reference list I could simply cut the output from STDIO and paste it into the source code window From STDIO you also have access to a very limited set of commands For those that know it the A File Edit Execute Hake vir if if feve if Ind MAEA Search Windows Info i CESTNE E i Tool Configuration Paes To or RELUDI RL LOTT TE RC CCOM TTP RESOURCE PRG RM MAKE TTP a2 Taggles soete unma Any of the programs supplied with MLC can be made RAM resident Laser shell operates in a similar fashion to the Macintosh Programmers Workshop MPW Megamax started off developing for the Macintosh The Editor Although the editor is part of the shell it is easier to treat it as a separate program Up to five files can be kept in memory at one time and you can cut paste and copy between them to your hearts content Standard GEM windows are used although the scroll bars are a Megamax invention to allow very fast smooth scrolling at a minimum of 10 lines per second All the features of the original editor have been carried over to Laser although you are no longer restricted to files of less than 32k and control keys are handled more intelligently The autosave option has been improved you can now choose the maximum time between saves and all dirty files are automatically saved before executing your program Nothi
76. ng very remarkable has happened on HODNIK C EES m ESNS File Operations i ESRC STREXP C wC i E W FI ee AVE NEW_FSEL laasia A DA Move M o Bytes 4861 Hod TAs 16 47 miala Cn em GNSILIB ARC ARC ARC COOKIE ARC OKIE C COOKIE DAT All the usual file management routines are built into the shell Unlike GEM Desktop copying files doesn t require endless disk swapping with a single drive 48 Volume 1 Issue 5 the search replace functions apart from some bugs being eliminated You can search forwards and backwards and replace once or always with and without confirmation The search string is taken literally wildcards or anything more useful haven t been implemented Strangely the option to ignore case still appears as a separate menu bar entry rather than being part of the search replace dialog the obvious place for it I would have thought The Compiler Megamax appear to have bought in the actual compiler from a company called Digital Lynx no I haven t heard of them either rather than improve their previous compiler The compiler is still of the single pass variety and conforms to the original Kernighan and Ritchie K amp R definition of the C language with a few extensions or to put it another way the compiler and library are not up to the forthcoming ANSI standard There are no restrictions on program or function size Libraries Two libraries are included with Lase
77. ns you have to make your own Quick library and load that each time you start Quick C The process is quite laborious and not really worth the effort Compilation is really fast and options are available to write the object code to memory an OBJ file or an EXE file Minimal optimisation is supported and all files are compiled using the medium memory model single data segment multiple code segments there is no support for any other memory models If errors are detected the last 26 errors are remembered and displayed at the bottom of the screen while you make the corrections Linker errors however get written to a separate file and you need to load and read this file to fix them I discovered that Quick C doesn t always generate the same object code as it s big brother Some complex macros cause it to throw up and others get compiled wrong So if you find a really tricky bug have a go at compiling the offending code with the optimizing compiler and seeing if the code works then This is an approach that I ve had to take a few times As far as Quick C is concerned the moral seems to be keep it small and simple The README QC file supplied with the package lists all potential problems The debugger can be called up anytime and only works on source lines The user interface is a subset of CodeView but there is no provision for viewing the object code You cannot view the contents of variables without placing them as watchpoints and there
78. nt anyway For further information don t bother contacting Borland they ll just refer you to the guys and girls state side who probably know nothing about it either Instead drop a line to Softpaquet PB6250 2702 AG Zoetermeer Netherlands Microsoft C Version 5 1 from Steven W Palmer Membership 8712 Now optimizing and capable of handling OS 2 and DOS Steven Palmer puts the latest version under the microscope Microsoft s latest C compiler comes courtesy of a huge package seating three voluminous manuals a quick reference guide a Quick C Programmers Guide and at least eleven disks For people used to dealing with the company this should come as no surprise The whole package exudes an air of professionalism Versions 5 1 and later caters for OS 2 as well as DOS development OS 2 executable versions of the compiler editor debugger and dynamic link libraries are supplied together with a number of batch files which let you create bound versions for running in both environment We only have MS DOS at the moment so I can t comment on the OS 2 side of the package This whole review is based on the DOS version Two of the 5 25 disks are in high density AT format and contain all OS 2 specific files The other disks can be read by any standard XT disk drive You can order disks in either 5 25 or 3 5 format and Microsoft provide a free conversion from one format to another We just linked an XT and a PS 2 and used Procomm to
79. ocation In RAM Of Variable At Run Time ae n printf Count d n tAddress of Count 1X n Count amp Count fk Same again 33 Volume 1 Issue 5 printf Increment d n tAddress of Increment 1X n Increment amp Increment puts Press Return Enter key to exit getchar So having run the program you might get the results Count 32 Address of Count 25712 Increment 97 Address of Increment 35710 Graphically this would look like Figure 1 The Address Of Operator In POINTEX1 we used the ampersand amp which will tell us the address of a variable This in itself is not terribly useful but we have to start somewhere One thing to note is that auto class variables are local i e they effectively vanish when the function terminates so having a static global pointer to an auto local variable is a sure recipe for disaster Why Use Pointers Now we know what a pointer is we come across the slightly more difficult question why use them Three reasons really e Speed If you ve ever dabbled in assembly language then things like address register and indirect addressing are two terms you II no doubt have come across Do remember that C is really only one level above assembly language in the machine accessibility stakes Many things you do in assembler have a direct equivalent in C and pointers are the nearest thing
80. of the slider If you want to accept the user s request just make the call wind set wh WF VSLIDE msg 4 0 0 0 Corresponding horizontal mnemonics are WM_HSLID and WF_HSLIDE Note that this wind _ set call will not cause a redraw message to be sent You must update the display to reflect the new scrolled position either by executing a redraw directly or by sending yourself a message If the document within the window has some structure you may not wish to accept all slider positions Instead you may want to force the scroll position to the nearest text line for instance Using terms defined in the last column you may convert the slider position to document units with top_wind msg 4 total doc seen _doc 1000 top doc This will probably require 32 bit arithmetic After rounding off or otherwise modifying the request convert it back to slider units and make the WF_VSLIDE request The other four slider requests all share one message code WM_ARROWED They are distinguished by sub codes stored in msg 4 WA_UPPAGE WA_DNPAGE WA_UPLINE and WA_DNLINE These are produced by clicking above and below the slider and on the up and down arrows respectively I have no idea why sub codes were used in this one instance The corresponding horizontal slider codes are WA_LFPAGE WA_RTPAGE WA_LFLINE and WA RTLINE What interpretation you give to these requests will depend on the application In the most common ins
81. or for a nominal handling charge Modesty forbids me from mentioning the fact that two of my programs are available in the catalogue one on the front cover S W S L have quite a good selection of stuff for the Atari ST C programmer I counted 28 disks all with a very high content of C source code and or C programming utilities All standard volumes are 3 00 each or 2 50 if you order 4 or more at a time For a copy of the catalogue just write to The South West Software Library PO Box 562 Wimborne Dorset BH21 2YD Watcom C Version 7 If you are getting a bit bored with M cr s t C the latest version of the Canadian Watcom compiler looks set to blow it right out of the water Watcom stands a very good chance of being the first ANSI validated compiler but in the mean time offers better optimisation than MS C smaller executable and more dhrystones Watcom comes in at a very respectable 250 about the same price as M cr s t C or if your budget doesn t stretch that far Watcom Express is a mere 60 A full review will appear soon if you can t wait contact the ubiquitous Grey Matter on 0364 53499 or at 4 Prigg Meadow Ashburton Devon TQ13 7DF Swifte C For Mirage Sahara Software Ltd are due to start shipping the Swifte C Programming Language Development System for MIRAGE this month see issue 3 for a review of Mirage Mirage itself is a multi user multi tasking OS available for the Motorola 680x0 family and has been
82. ould become more frequent the Source Library a collection of public domain C source code available at minimal cost to all members more details on that inside and finally local groups If you are interested in either setting up a local or special interest group then read Francis Glassborow s column in this issue When you ve read it do something about it We also want to hear from each and every one of you telling us what you re doing what projects you re working on what you think of the group what you like and dislike about C any bugs or problems you ve encountered along the way We ll do all we can to help you get the most out of C and the C Users Group U K it is after all your group We are not a commercial profit making group What we aim to be is professional with your input Phil Stubbington Editor Volume 1 Issue 5 EGitorial ss eeire cc eea a a a eedenbockate 1 Wotz Nu by Phil Stubbington s cvdeviinrcccAaaenGediwe 3 Microsoft C Version 5 1 from Steven W Palmer Membership 8712 4 Writing Portable C Programs by Ron Wellsted csc cca tisss toca ern cuhivan ood 9 Professional GEM Dy TIM OPE ee naa ots tava dvedate 12 Structure Part 5 by Colin Masterson cccccsccsseesseeeeteeeeeeees 18 The Story Behind FLIT by Colin Masterson cccccccescesseeesteeeeeaes 20 The Source Library by Martin HG UStonissccsi2ccncesteeseessucaicavedaaielavecteds 29 The Dreaded Pointer Part 1 by
83. ow calls which are useful to advanced programmers They require techniques which I have not yet discussed so you may need to file them for future reference The AES maintains a quarter screen sized buffer which is used to save the area under alerts and menu drop downs It is occasionally useful for the application to gain access to this buffer for its own use in saving screen areas with raster copies To do so use wind get 0 WF SCREEN amp loaddr amp hiaddr amp lolen amp hilen Hiaddr and loaddr are the top and bottom 16 bits respectively of the 32 bit address of the buffer Hilen and lolen are the two halves of its length Due to a preculiarity of the binding you have to reassemble these pieces before using them The actual value of WF_SCREEN is 17 this does not appear in some versions of the GEMDEFS H file If you use this buffer you MUST prevent menus from dropping down by using either the BEG_ UPDATE or BEG_MCTRL wind update calls Failure to do so will result in your data being destroyed Remember to use the matching wind_update END_UPDATE or END_MCTRL when you are done The other useful call enables you to replace the system s desktop definition with a resource of your choosing The call wind set 0 WF NEWDESK tree 0 0 where tree is the 32 bit address of the object tree will cause the AES to draw your definition instead of the usual gray or green background Not only that it wil
84. parrow EGA graphics routines Languages 2 two subset C compilers cpcn and ratc with sources an interpreter sci as MS DOS executable only and a number of Unix style utilities Games 1 the Dungeons and Dragons style game Larn Should be possible to get it running on most systems Requires lots of memory to run Volume 1 Issue 5 Please remember that double volumes must be ordered together and will cost twice as much At present this covers volumes 23a amp 23b 24a amp 24b and 25a amp 25b Your own contributions are always welcome 15 16 17 18 19 20 21 Unix Utilities 3 source for LEX lexical analyser for MS DOS but should be possible to convert to other OS s Unix Utilities 4 lots of material related to lex amp yacc yet another compiler compiler Unix Utilities 5 another parser generator like lex called Bison Source is included but documentation is minimal so some detective work is called for Any offers Software Tools 2 some more programmers tools see volume one and a simple Unix Curses type screen library Minix 1 conversion of the Kermit comms program Conversion and documentation of use to any Minix devotee by Adrian Godwin Unix Utilities 6 mainly a healthy bunch of benchmarks but also a number of general purpose utilities Games 2 the one that started it all off the Coloss
85. poor librarian cannot be expected to be an expert on every program in the library LIBRARY LISTS Each issue of C Vu will contain a list of what is in the library In addition to this a separate totally 30 Volume 1 Issue 5 up to date list is available to anyone who sends a large S A E together with 20 pence in stamps to cover expenses The library list is also available for download from the Chronosoft BBS or Dr Solomons FIDO details in C Vu If you are looking for something in particular then contact me and I shall try to find it for you LIBRARY ORGANISATION Each library disk will be dedicated to a specific subject area as the range of material in the library permits For instance material that is strictly of interest to people with IBM PC compatible hardware will be isolated from generally portable material This division is made on the barest aquaintances with the program I cannot guarantee that everything in the generic section is suitable for all machines the specific machine divisions are for programs that are OBVIOUSLY only of interest to owners of a specific machine When a library volume is strongly suited to one particular type of machine in this way the list will say so to save people ordering disks that are of no use to them Needles to say the C Users Group can offer no warranty as to the quality and fitness for any purpose of anything in the library Public Domain programs are almost bound to have bugs in them it is
86. program then you may have any standard volume from the library copied on to the disk for no charge The Librarian reserves the right to judge what is a sensible contribution to qualify for a free volume sending a disk with hello world on it will not get you off paying the two quid CONCLUSION I hope that this has given you an insight into how the library is intended to work Hopefully the library will become the focal point of the activities of the group as there is much in it as topics for discussion and development I hope you find the charges are reasonable the library takes a lot of time amp machine resources to run effectively so it cannot be a free service Two pounds for over 300k of C source code amp related material is very good value for money and goes some way towards contributing to the running costs of providing the library One final word the library is only going to be any good if it is USED If it is used well with people contributing as well as taking then it could grow into a valuable resource for the C Users Group amp all C programmers The Dreaded Pointer Part 1 by Phil Stubbington The cause of nearly all bugs Phil Stubbington investigates Introduction When I was first trying to gt to grips with C pointers were the feature of C that caused most problems What were they why were they there are they the same as pointers in Pascal Why did my programs crash spectacularly whenever I started trying to
87. py and we will be looking out for updates from the original authors An Amiga expert shouldn t take long to modify it to run on that machine Ron has already tested it as a cross compiler on a PC so as soon as an Amiga owner comes up with the relevant source mods for that machine a version can be compilled and ported for that part of the C community Anyone else who is interested in getting to grips with compiler writing will find Sozobon an excellent place to start If we can find the right enthusiast with enough time we might even manage to produce an ANSI standard PD compiler and then prehaps follow with one for C Don t forget that it can compile itself so you can steadily work at improving what is already better than a number of the sub fifty pound offerings It will cost you very little Note that the libraries are in source code so that these will be of more general use and interest and not much will need to be done to get the library manager to function with your favourite compiler The professional C programmer may wonder why I am raving about a product that is clearly inferior to their professional development systems The answer is simple this is an entirely open package at a cost that even the poorest of enthusiasts can afford Eee Volume 1 Issue 5 Winding down A word to the experts everyone knows something you don t and once you knew nothing so be patient with the ignorant A word to the ignorant the experts once knew
88. r C The standard library contains what Megamax term a large complement of Unix routines as well as a full set of GEM functions Routines are also provided to access the Line A graphics primitives on the ST useful if you want to use graphics but don t want to do all the programming that GEM involves Most routines have been coded in assembler for extra speed The second library is used in addition to the standard library and is a pseudo debugger Normally debuggers come as separate programs but the Megamax debugger actually becomes part of your program Other than that the library provides most of the facilities you would want from a debugger and has the added advantage of being extendable Utilities Around sixteen additional utilities are provided Some duplicate functions built into the Laser shell I shall briefly describe three of the major utilities the first two started off life in the Unix world e egrep allows you to search for complicated patterns in text files Generating cross references is one application Very useful for documenting e make reads a makefile which tells it how to rebuild a particular program Really only of use if you have several source files when it becomes essential This is a full implementation the Metacomco make isn t e rcp resource construction program Allows the easy creation of pull down menus dialog boxes and icons Has the dual purpose of being useful in prototyping as well as
89. robably two bytes but ptrToInt is pointer sized probably four bytes i e sufficient to hold a machine address The full declaration is int ptrTolInt Note that as usual because it is an auto class variable in the example it is guaranteed to contain rubbish unless we initialise it Initialising A Pointer In the example we have initialised ptrToInt so that it contains the address of the variable called count As before we find the address of a variable by using the ampersand ptrToiInt amp Count Reading A Pointer Variable We have now initialised the variable ptrToInt Again as with any other type of variable we can assign a value to it as we ve just done or read the address back out again printi ptr Toint 239xX shi Mites An PEETOIN GA cages tts Reading What The Pointer Points To Finally we can find out the contents of the address that the pointer is looking at printet OT poe eed Contents of ptrToint d n ptrToint Note the subtle difference Just referring to the pointer name alone yields the address Prefixing the pointer name outside of the initial declaration with an asterisk yields the contents of that address Before you compile and run the following program write down on a piece of paper what results you expect to see Obviously unless you re a mind reader you won t know the actual run time addresses and that isn t the point of the exercise anyway So just make a wild guess
90. rt of programmers dating agency Some of the programs already in the library such as the xlisp lisp interpreter and bawk text processing language are complex enough to need some joint effort to get to grips with them ORDERING Library material is available to CUG MEMBERS ONLY and the standard rates are shown in the Source Library listing Specially selected material incurs a 4 00 surcharge on the standard rates PLEASE NOTE that if you want a single sided 3 5 disk then please say so when you order The 3 5 drive on my XT machine where the library is kept will not format single sided disks so any single sided orders have to be processed through my Apricot F2 I know that Ataris come with a single sided disk as the cheapest option but I should think that anyone thinking about C 31 Volume 1 Issue 5 compilations would have at least a double sided drive Am I wrong If so please tell me The surcharge of 4 pounds is made for a library order other than one of the standard prepared disks When the data base system is in operation it will be possible to look out a selection of files matching certain criteria This takes time however so the surcharge is made The surcharge will apply to every multiple of 360k of data selected I hope that my efforts in sorting out the library volumes will mean that no one will ever need the special service If you are donating material for the library or are returning an improved version of a library
91. s are already supplied However when I tried the Brief configuration I found several common keystrokes were unemulated or different I couldn t move to the end of the file using Ctrl and End the editor reported that the keystrokes were unassigned However I was able to modify the configuration file to make it closer to Brief Even so I finally gave up and went back to Brief Volume 1 Issue 5 The Compiler The compiler consists of four programs CL EXE C1 EXE C2 EXE and C3 EXE which contain the main program the preprocessor and lexical analyser the parser and the code generator and optimiser respectively For large programs a large model version of C1 EXE is supplied which can compile programs that normally cause heap errors under the default version The large model version of C3 EXE is no longer supplied Compilation is noticably faster than earlier versions and generates better quality code The optimiser now handles loop optimisation and common subexpression elimination in addition to those available in version 4 Some library functions can be compiled inline which improves overall program speed by eliminating the overhead of calling them as extrinsic functions However it still falls down on some occasions such as failing to eliminate redundant storage allocations Be warned that some programs compiled on full optimisation will probably behave differently from the non optimised versions To be fair Microsoft recognise this and explain
92. se of the library volumes mentioned herein NAg Games 3 Maurice Watson s QL eae Why not contribute some of your own Wom version of Volume 21 Colossal Cave RAAE work or conversions of existing library See the article in this issue volumes to other systems Non machine specific contributions especially welcome To order any of the volumes in The Source Library simply circle the appropriate volume numbers in the space below you can photocopy this form and send it with the correct payment to The Source Library C Users Group U K 36 Whetstone Close Farquhar Road Edgbaston Birmingham B15 2QN Please send me the volumes I have circled below 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23a 23b 24a 24b 25a 25b 26 _____ volumes at 2 00 sending your own 5 1 4 or 3 1 2 disks __ 00 _____ volumes at 3 00 on our 5 1 4 disks 00 volumes at 3 50 on our 3 1 2 disks TOTAL 7 I enclose a cheque postal order for __ made payable to C Users Group U K Membership Number Signed SAR Volume 1 Issue 5 Why Programming Why C by Donald Wilcock I had bought my computer which was to be my belated introduction to the mysteries of computing in April By the time that it came to September obviously I still did not know very much about it It is difficult to say now exactly what I expected to gain from some knowledge of programming I think that I have come to believe that
93. seconds using the supplied RAM disk program rdy Even with autosave on so the source file would be saved before the compile started the figure only increased to 42 seconds To get some idea of execution speed I ran the Dhrystone benchmark Version 1 1 which is generally regarded as a better indication of performance than the Sieve benchmark which is normally quoted MLC gives a figure of 852 iterations per second compared with 1149 for Mark Williams and a dismal 650 for Lattice C Higher figures denote better performance Although I haven t had the opportunity to test it yet Manx Aztec C is likely to beat the lot Conclusion As with any computer language the developers have had to make a compromise between speed of compilation and execution MLC is over 300 faster than Mark Williams C on compilation and 26 slower on execution Compilation speed affects everybody but the biggest difference in execution speed is brought about by using better algorithms not by any optimisations the compiler does The Laser shell is a vast improvement With the previous version and with all the text based shells I have tried including Mark Williams msh and gulam which is bundled with Aztec C I tend to drop back to good old GEM Desktop to carry out simple operations like deleting and copying bunches of files for speed As I have already mentioned the Laser shell is actually faster than GEM Desktop and the editor is sheer bliss Document
94. t to automate the installation of the compiler and other tools This is standard with almost all their other products and is certainly easier than the D I Y approach offered in version 4 0 Running the setup program offers you a list of possible configurations DOS or OS 2 versions or a bound copy that will run in both modes small medium compact or large model libraries floating point emulation or coprocessor support different editor configurations emulating Brief tm WordStar or the Epsilon editor and many other minor options If you elect to install the whole lot you will need at least 8Mb spare hard disk space The MSC EXE compiler driver is no longer supplied with the package and has been replaced by the command line driven CL EXE utility for Xenix compatibility If you have any batch files containing MSC then Microsoft offer guidance on converting them to the CL format Library There are separate run time libraries for each memory model and during installation you are given the option to combine the floating points library and graphics library together with the main library Such combined libraries take up more disk space but linking is faster as a result The total size of the combined libraries for all four memory models is just over 1Mb Volume 1 Issue 5 The major improvements over version 4 0 is the inclusion of bit mapped graphics functions and low level DOS and BIOS functions The graphics functions support all graphics modes
95. tance text documents the customary method is to change the top of window position top_ wind by one line fora WA_UPLINE or WA_DNLINE and by seen_doc the number of lines in the window fora WA_UPPAGE or WA_DNPAGE 16 Volume 1 Issue 5 After making the change compute a new slider position and make the wind_set call as given above If the document s length is not an even multiple of lines or pages you will have to be careful that incrementing or decrementing top_wind does not exceed its range of freedom top_doc to top_doc total _doc seen_doc If you have such an odd size document you will also have to make a decision on whether to violate the line positioning rule so that the slider may be put at its bottom most position or to follow the rule but make it impossible to get the slider to the extreme of its range A COMMON BUG It is easy to forget that user clicks are not the only things that affect slider position If the window size changes as a result of aWM_ SIZED or WM_FULLED message the app must also update its sliders if they are present This is a good reason to keep the top of window information in document units You can just redo the position calculation with the new seen_doc value and call wind_set Also remember that changing the size of the underlying document adding or deleting a bottom line for instance must also cause the sliders to be adjusted DEPT OF DIRTY TRICKS There are two remaining wind
96. terface Of course to do this may require a bit more complexity in our actual copydir function but this is a very useful technique In general we could visualise an application program as being a loop calling to each function in turn If the function has nothing to do then it does nothing It is up to each function to keep track of its own internal status I have not used this method here although I have used it in more complex applications where the overhead is justified A Collection of Functions There are one or two other functions worthy of a mention user_win A general purpose split window user input function You pass details of the size and position of the window the function to be called to paint the text at the top and bottom and the function to be called to get user input All the user input in FLIT is handled through this function pct complete A pretty moving bar display used to give the progress during a format operation I must admit to having a liking for functions which are clearly contained within a single module which are called with a mode flag to determine the operation of the function Pct_complete is a good example It is a general purpose function which can be called with any current value and corresponding full scale reading and will display the graphical pointer in a window Since the function employs a window library to save patches of the screen and paint the image it requires to be initialised before use
97. to address registers e Accessibility We ve mentioned that pointers contain the address of a memory location That memory location could well be the control register for a hard disk controller So if the mood or need takes you C can be used to control a multitude of devices without having to drop into assembler e Tina Yup There Is No Alternative As we II discover later on there are some things you can t do without messing around with pointers One of these is using dynamic memory If the exact memory requirements of your program aren t known at compile time then you can t really avoid using pointers An obvious example is the text editor or word processor You don t know at compile time what size the file is the user wants to load and you don t know how many lines they II add and delete after it is loaded Pointer Declarations In our second example we are finally going to introduce a pointer Like any other variable we have to declare it before we can use it A pointer again like any other variable has a name and a type In this example we declare a pointer called ptrToInt We know it is a pointer because the name is 34 Volume 1 Issue 5 prefixed by an asterisk We also know that it is a pointer to an int because that is the type given to it So the declaration is best read from right to left We are declaring a variable called ptrTolInt which is a pointer to an int So the object that ptrToInt points to is int sized p
98. ty i e 100k disks can also be accepted The alternative is to upload articles to CIX as detailed elsewhere in this issue Ideally the only formatting in text files should be a double CR LF between paragraphs and between EACH line of source code if using examples etc Generally speaking source code of great length will not be reproduced in C Vu but will be placed in the Source Library Screen dumps are always welcome IMG GEM PI i e Degas IFF and MacPaint can all be accepted but must be on DOS format disks Lastly please remember to include your name in any text files otherwise we may be unable to include a By line Megamax Laser C by Phil Stubbington The Next Generation Why Choose C C is NOT a beginners language like Pascal or BASIC C was developed to give the programmer the power of assembly language well almost while retaining the readability of high level languages Consequently things like run time error checking are entirely up to you The disadvantages to this are obvious but on the plus side is does make C very fast and versatile A language like Pascal gives you no option when it comes to errors Type in a number that is too large and the program will stop with a message like Integer overflow at line 90 In C you could write some code that checked the number and ask the user to re enter the number if it was out of range One of the other advantages of C is that it is such a widely used language th
99. upgrade the contents of the manuals are exactly the same The run time library manual is well organised with at most one function per page together with prototypes descriptions examples and cross references An appendix at the back describes differences between routines and variables common to MS DOS and Xenix It is easily the best documented run time library that I have seen and it is very extensive The utilities manual contains a user guide for the CodeView source code debugger the Microsoft editor the linker librarian and other small utilities The rest of the manual contains a C language reference guide which makes concise reading Nothing in the package makes any attempt to teach you C programming Microsoft assumes that you have access to other literature and even lists some recommended sources The last manual is thinner and describes the C compiler in considerable detail There are chapters on writing portable programs programs that will eventually get blown into ROM and discusses memory models and cross language programming Very little is omitted and it is well organised In the six months that I have had the package I have hardly found an occasion where I couldn t access a certain piece of information All three manuals are indexed and have subject divider tabs for quick access to the required section They also make ideal weight training during those slack lunch hours Installation Microsoft now supply a SETUP EXE produc
100. use them Then one day a sudden flash of inspiration I try to make the most of those they don t happen that often The purpose of this article is hopefully to reduce the bashing head against brick wall phase Let me know if it succeeds The Starting Point Right first things first I m assuming that you already know the basics of C you can quite happily cobble together a program off your own back In particular you should already know about the various types of variable char int long float and double You should also know how and where they are declared auto and static classes Equipment wise I ll assume you have access to a C compiler linker etc and appropriate documentation The example programs to accompany this series have all been written using the Prospero C system but should work perhaps with minor mods with any C compiler which has leanings towards the ANSI draft standard Rec ee Volume 1 Issue 5 What Is A Pointer This is no doubt going to sound incredibly obvious but a pointer is a variable able to hold the address of a C object either a variable or a function There are two types of pointer explicit and implicit For the time being III ignore implicit which are compiler generated to handle arrays and concentrate on the explicit ones i e ones which appear as a result of declarations made by you in the program Once a C program has been written compiled into machine code and linked with
101. volume 14 Larn is Squeezed so that the files fit onto a 360k volume Source of the unsqueeze program is provided so that it should not take much effort to get at them If you want to download software off one of the online systems CUG sponsors then you will need an ARC program as the library files will be available online in ARC format to save space amp download time Please do not expect to have the whole library available on a BBS It is up to the SYSOP to decide how much disk space he is willing to spare for CUG library use If you cannot cope with an ARCed file then a kind message to the SYSOP of the board may result in the files being left un ARCed for you to download individually Except for a few documented exceptions everything in the library must be in source code form The library will only carry shareware function LIB files on disks that are indicated to be for one type of machine only If a library disk contains material that can only be used by one type of machine this will be indicated in the library list Most library disks will be usable by any machine with adaptation in some cases For some programs an MS DOS COM or EXE version of the program is included You run this 29 Volume 1 Issue 5 program at your own risk In most cases it is the executable that was given to the library at the same time as the source but I cannot guarantee that it works is the same program is not malicious a Trojan Some but not all

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