4. Object-Oriented Programming
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1. X x1 2 x2 3 int i p x2 x1 2 O K 2 is converted into X 2 using constructors i X2 O K x2 is converted into int using operator int x2 xl p error types do not agree Appropriate constructors convert common variables into objects of desired type Conversion of an object into another type requires a conversion function That function is defined the same way as the operator function but instead the name of the operator you need to give the name of the target type it is legal to give a pointer to the type e g operator int In the example above x2 is converted to int and the result is assigned to variable i The last line of the example is an error since the compiler does not know how to add an object of class X and the pointer to type int 4 13 Dynamic allocation of memory Dynamic allocation of memory is known to the users of C In C this feature is raised on the level of a language Instead of library functions malloc and free we have new operators new and delete This feature exist in AleC too 4 13 1 Allocation operator new Pointers can point to address of a static variable but can also point to a part of memory allocated under heap free memory whose addresses increase toward to other end of the stack Allocation can be sufficient for an object of a certain type as well as for a number of such objects int p new int 4 bytes allocated int size 20 4 Object orient2. Destructors bear the same name preceded with the character as the originating class Destructor do not return any result nor accept any parameters which is the reason why destructors cannot be overloaded Compiler calls them immediately before an object is destroyed in order to free the memory occupied by the object except in the case of global or static variable when they are used at the and of the simulation or on leaving the main function If the command return appears before the end of a block destructors are called before the exit from a function As in the case of constructors destructors cannot be static objects class X rants class members public 38 Alecsis 2 3 User s manual X Destructor for class X 4 10 Operator overload C programmers know it is possible to declare variable types of structures but that little can be done with them using current C operators Structures can be copied into each other can be passed to functions returned using return and that is it We are describing operations with objects and not their particular members Structures cannot be added because compiler does not know how to do it that is instructions for addition of operands that are not integer or real do not exist Operator overload mechanism explains to compiler how to apply the existing operators to object of class type 4 10 1 Global level overload Overload of operators is possible by defi
3. Friendship declaration does not mean passing an object as an implicit argument thus an object must be passed explicitly to the function Therefore global function cannot use this even when declared as a friend The example above shows that a method of one class can be friend of another The friendship declaration does not change the meaning no matter what area of the class it is situated in public or private A method and a friendly class with the same parametric profile do not cause warning messages about redeclaration 4 8 5 2 Friendly classes If the intention is for all the methods of one class to have access to all the members of another class the first class can be declared as friendly class X class Y int xval yval friend class X can do without class This approach makes the job easy but you need to be careful since if everyone is defined as friend than the whole system loses meaning since everyone can change data 4 9 Constructors and destructors It is possible to declare arbitrary number of methods inside a class Those methods are called explicitly as any other function Some other functions have special meaning and are the basis for object oriented programming in AleC Variables declared within an area of visibility most common way using have existence period ending with the closing of the area of visibility most likely using Compiler allocates enough space for those variab
4. Default values of function parameters We expanded the ability to have default value of parameters in Alecsis to include specific simulation constructs If an actual argument does not appear on the appropriate place its default value is placed there This enables function calls in many different ways with the parameters always defined fl int i double j int k 2 k has the default value 2 int p f1 2 2 3 parameter k is set to 2 tnat gre 1 2 5 2 74 here k equals 7 The only restriction in the number and type of the parameters with initial values is that all parameters to the right from the first parameter with the initial value have to have initial values as well An overload of this function can confuse the compiler char f int int 2 int error the third argument does not have a default value int fp int fp int double 2 2 two versions of fp int pl fp 1 5 6 O K call of the second version of fp int p2 fp 1 both variants are suitable conflict Note All initial values have to be constant expressions 4 5 Inline functions Ordinary functions are translated and stored in the library and linker finds them if used in the code It pays off to insert the function in the code instead a function call in case when the function is only a few lines long as the time needed to for the function call is longer that the time of function execution in such case The precondition is
5. c3 cl operator c2 a classical method call c3 cl c2 a real overload AleC allows overloa of existing operators but it does not allow for a definition of new operators because that would introduce confusion into the rules concerning association and priority 4 11 Overload of operator Assignment operator can be overloaded as any other operator but certain restrictions apply When inheriting see the section on inheritance every derived class has to give its own version of the operator since the definition of the operator is not transferable Further on to cover all the applications of this operator you need to define a copy constructor constructor takes the reference of the source class These definitions apply to the following cases initialization of objects e g X x1 x2 x1 copying of objects x2 x1 40 Alecsis 2 3 User s manual passing the object as an argument of the function call transfer by value return of the object using command return 4 12 Overload of implicit conversions You are by now familiar with the rules regarding the conversion of operands of different types The user can add a new conversion to the list of legal conversions so that the new type class functions in the same manner as an inrinsic type For that you need appropriate constructors and conversion functions class X public X int operator int amp X X operator X amp X amp
6. compiler will not report redeclaration if all of them have different parametric profile type and number of parameters In the moment of the function call compiler decides which function satisfies the actual call the best taking into consideration the number of implicit conversions that will have to be applied to arguments double f1 int the first declaration double f1 int copy O K int 1 int error difference is in the returned type double f1 int const char O K different profile double dl f1 2 call to f1 int double d2 1 3 string call to fl int const char Compiler will easily find its way around an overload of the name of the function if it has the information about the profile The linker however cannot determine the version based solely on the name of the symbol 30 Alecsis 2 3 User s manual Alecsis linker uses type safe linkage It secures the uniqueness of the function name by adding an especially coded parameteric profile name mangling to that name For instance the first version of 1 in the symbol table of linker will be 1 i having one integer parameter the second 1 _iPc having one integer and one pointer to character as parameters One should note that the function overloading is very useful for simulation especially logic simulation One can create a single name for a logic operator for instance and gate which can have two or three inputs 4 4
7. def ine and then use that name in the program define PI 3 141 ANSI C and C introduce variables whose value should not be changed in the program 2T 28 Alecsis 2 3 User s manual const double PI 3 141 constant of type double const No 123 constant of type int These constant has to be initialized immediately upon declaration unless it is an external variable since that is the only place initialization can be done Interesting effects can be produced using combinations of qualifier const and various pointers as the following example shows const c 2 constant int type const pc amp c pointer to a constant int const cp pc constant pointer const const cpc amp c constant pointer to a constant int vp amp c error pointer must not point to a constant Pointer pc can be changed afterwards in the program but not the value stored on the address it points to This is possible to do in the case of the pointer cp but in this case the value of the pointer cannot be changed Finally neither the value of the pointer cpc nor the value on the address it points to can be changed The last example illustrates a semantic error if it was allowed for the pointer vp to be set to the address of constant c the value of the constant can be changed indirectly using the pointer Qualifier const can be used with function declaration too The declaration of standard library function strcpy
8. exactly the passed object and is manipulated as any other object of the same type 34 Alecsis 2 3 User s manual In C the keyword this refers to the pointer of the object passed to the appended functions so the access to the individual members requires the operator of indirection gt eg this gt xVal this gt yVal Alecsis virtual processor uses a table of pointers to the sources of the most frequent operands and is able to treat this as an object and not an operand This renders dereferencing of the word this unnecessary which can save time in larger methods Access to particular members is possible using operator eg this xVal this yVal Nevertheless we intend to change this to be the same as in C in the following releases of Alecsis not the confuse the user You can explicitly use this in order to differentiate the names of the class members from names of other variables in case of masking of the members of the class The second option is to list names of classes and using the resolution operator class X int x Yy public void setl int x int y t void set2 int x int y X 4 8 4 Static methods and class members It is not legal to use all specifications the method of allocation extern register auto inside the body of a class Mentioned specification can be applied to the members and functions with different affects 4 8 4 1 Static members When objects of a class are defined eve
9. in C If that creates problems you can declare A as virtual class Regardless of the complexity of the hierarchy this class can appear only once in the final hierarchy 4 14 4 Construction and destruction of derived classes A derived class and its base classes can have constructors When an object of the derived class type is declared the compiler calls the constructors of the base classes in the order of inheritance and then it calls the constructor for the derived class However if a virtual class exists on the tree its constructor is called first The opposite happens with the destructor call first the derived class than base and finally virtual The situation complicates if constructors of base classes require arguments The arguments are listed in the definition not declaration of the derived class constructor class X int xval public X int x xval x class Y int yval public Y int y yval y class Z public X public Y int zval public Z int x int y int z X x Y y zval z 66 29 Arguments for base constructors are listed after the colon and can include all legal expressions The visibility area after includes formal parameters of the derived constructor source class and global variables Symbols from those regions can participate in the forming of the argument If a member of a derived class is also a class the arguments for the constructor c
10. is now 3 4 Object oriented programming 29 If you do not like the idea of being able to change an argument in a function you can always declare the argument as const You cannot change the argument now in the function but using references you can still save some time in the transfer of large objects 4 2 2 Local references Reference object inside a function is practically another name for the initializing object Local reference has to be initialized immediately after declaration bearing in mind that every change in the reference will affect the original object int i int amp ri i vi is a synonym for i ri 2 i is now 2 as well 4 2 3 Reference returning functions A function can return a reference under its name In this case the function call can be an value meaning that you can write into the function call This property is used mostly with the overloading of some operators The function has to return a valid reference which is not a local object because local object is erased during the return from the function dangling reference int amp f1 int int FI 2 3 4 In all three cases given above if the initializing object is not an l value or if the rules demand type conversion a temporary object will be created and its address will be used As this is usually unwanted the compiler will warn you 4 3 Function overload Multiple functions of the same name can exist in C and AleC The
11. the situations when it is not clear which variant of an object is used in case when symbols with the same name exists in different visibility areas It is widely used as a part of objects whose type is a class but it can be used independently int i global i main inte ip Jy local i and j j i refers to local i j i refers to global i 4 8 Classes Classes are a special case of composite types similar to structures They allow the expansion of the existing system of types Classes can have members data but unlike structures classes can encompass a number of appended functions These appended functions are methods which manipulate the objects overload existing operators to make them applicable to newly defined types as well as provide mechanisms of implicit conversion in case of dealing with changed types Fully defined class represents a type equal in status to already existing types We emphasize that classes differ form structures in that classes can have functions for members in version 2 0 C structures can too but this was left out in AleC Access to members stays the same as in C operators for objects and gt for pointers to objects class X int a double b char s 20 ie main X X PX X a X b px gt a px gt b 4 8 1 Access to class members Members of classes are data and functions They are local in reference to the class and cannot be refe
12. 4 Object oriented programming The given overview of lexical and grammatical rules focused on the common points between C C and AleC This chapter will also focus on similarities between AleC and its basis languages If the reader is not familiar with the object programming introduced by C C and this chapter is too succinct to explain it completely the authors suggest consulting one of the numerous manuals on the subject Object orientation enables better reusability of already developed program parts With this concept software is developed in phases layer by layer Diverse multifarious building blocks are developed first and then used to put together to form larger blocks which can be used again to build some other blocks Alecsis was developed to model large number of various electronic components and systems Many of them can be considered as composed of some building blocks That is why the authors included the construct of object programming in AleC and turned it into AleC Before we approach object programming we will discuss some rules of C not necessarily directly connected to object programming since we will need them in the coming chapters Those rules address functions overload standardized constants inline functions initial values of formal parameters etc 4 1 Constant variables You already read about constants in the chapter on lexical rules It is possible to name a constant by using the preprocessor command
13. an be passed using the same syntax Finally common members of classes can be initialized this way too For more details on this subject consult a manual of C 44 Alecsis 2 3 User s manual class X int xval Y y y has type Y class public X int x xval x y x 2 xval is set to x constructor for y obtaines argument x 2 4 15 Virtual functions Virtual functions are still not functioning in the current release of Alecsis The mechanism of late linking is a fundamental characteristic if not the requirement of object oriented programming All references to a method and functions are treated as global symbols used by linker in the early phases of the simulation If the linker is not able to resolve such references the program stops early linking Contrary to this late linking allows a late decision on the choice of the method even during the execution of the program when the method is invoked A method needs to be declared as virtual in the base class if the mechanism of late linking is to be used This allows redefinition of that function in a derived class A redefined function becomes virtual the word virtual is not necessary for it with the condition that the returned type and the parametric profile is the same as in the base class Virtual function cannot be static but can be a friend Global functions cannot be virtual Both base and the derived versions have to be defined or the
14. base function can be declared as purely virtual but the whole class becomes abstract class Base public virtual int foo int base version of foo hy class A public Base public int foo int redefinition of foo derived class Base b A a Base bp bp amp a bp gt f00 2 calls A foo bp amp b bp gt f00 2 calls Base fo00 4 Object oriented programming 45 Note that the assignment of pointer to a derived class to a pointer of a base class is legal and that the compiler does the implicit conversion The reverse is not legal without the explicit conversion cast operator Abstract classes have at least one purely virtual function Those classes serve as the basis for inheriting It is not legal to define an object declare a formal parameter or return the result using return if the abstract class is the type it is possible with the pointers or references of abstract classes class object public virtual void draw 0 purely virtual function class circle public object public void draw definition circle draw class rectangle public object public void draw definition rectangle draw E circle cl c2 two objects class cicrle rectangle rl r2 two objects class rectangle static object ob amp cl amp r2 amp c2 amp rl vector of pointer Assignment of addresses of derived objects is pe
15. ed except _ z lt now S ss ddt d2dt2 idt sdt In general binary operator in the expression op1 op2 can be overloaded using global function operatore top1l top2 where top1 and top2 are appropriate types of operands with the allowed 4 Object oriented programming 39 implicit conversions Unary operator 0 in the expression op can be overloaded using global function operatoro top where top is the type of operand with the allowed implicit conversions If the objects are large it pays off to pass them to the function by address binary operator function would be declared as operator topl amp top2 amp Operator function can be called as an ordinary function i e as affix c3 operator cl1 c2 but it is a matter of style to use it as an infix operator 4 10 2 Overload using methods An operator function can be a method of the class in which case all rules for methods apply class complex the same as in the class complex given before complex operator complex r return complex re r re im r im The method operator is implicitly defined as inline In binary operations those methods have one parameter only since the left operand is implicitly passed this Unary operator methods do not have parameters because the only operator is passed implicitly too You can call these methods either explicitly as members or as operators foo complex c1 2 3 c2 1 1 complex c3
16. ed by copying the object p2 constructor is not invoked If one of the mentioned ways is not used compiler will report an error In the case of object p3 compiler made a shallow copy of the object p2 by copying its bit pattern If an object involves a pointer pointing at allocated memory it is necessary to define a special type of constructor copy constructor which accepts reference to a class e g Point Point amp The object p2 would be passed by reference into that constructor where space would be allocated for the memory pointed by the pointer In that way the deep copy of the object would be made Constructor can be called in expressions as an ordinary function Than it creates temporary nameless object which is destroyed after the exit from the visibility area Initialization can be done using this temporary object Point p1 2 3 p2 Point 4 5 This means going the long way but temporary objects play an important role in the in operator overloads and implicit conversions Constructors for the objects created on the stack are called every time the control gets to their declaration place Constructors for global or static variables are called before the beginning of the simulation if one uses Alecsis simulator that is before the main function if one uses AleC for C like programs Constructors cannot be static functions They can have parameters with initial values just as any other function 4 9 2 Destructors
17. ed programming 41 char s1 new char size 1 allocated size 1 sizeof char char s2 char malloc size 1 sizeof char C style Point pl new Point 2 3 new constructor call Point p2 new Point default constructor int i new int 5 pointer i allocated and set to 5 Command new is used for memory allocation regardless of type In contrast to malloc you define a type and not a number of bytes because the compiler calculates that number automatically In case you are allocating pointers to classes you can pass a list of arguments to the constructor too You can also set a value pointed by some pointer to a particular value Allocation of a vector has a restriction constructors with arguments are not allowed only default constructors Point vp new Point 5 Operator new can be overloaded to increase the control over allocation If you do that you can access the standard global operator using access resolution new 4 13 2 Deallocation operator delete Already allocated pointer to an object needs to be deallocated when leaving the visibility area in contrast to objects pointers to objects need to be explicitly allocated using new and deallocated using delete otherwise the memory they point to will not be accessible nor free which can cause unpleasant consequences delete i frees the pointer i delete pl call destructor Point frees pl delete 5 vp calls dest
18. ethods have the right of access All methods are defined within the class and are therefore inline Overloaded method set gives them their values show displays them on the screen while methods Xval and Yval return their values These are the only legal operations with the object of this class Restriction of possible operations on members of a class is a valuable advantage of object programming since it limits who and how can change objects of a particular class Errors are easier to find since it is always specified who is responsible for a particular operation f1 Point pl p2 int x y pl set pl xVal and pl Yval are set to 0 p2 set 2 3 p2 xVal 2 p2 yVal 3 pl show p2 show xX pl xVal error xVal is a private member y pl Yval O K Yval is a public method 4 8 3 Keyword this In the previous paragraph methods have referenced members of the class as if these were known to them in advance All methods have an additional level besides usual levels of visibility class level This level is narrower in the order of searching than the global but wider than the level of formal parameters This means that a class member masks global variable of the same name while a formal parameter or a local variable masks the class member The class object whose members are used is passed as a hidden parameter in every appended function This can be made visible using the keyword this This keyword represents
19. given below indicates that only string dst changes within the declaration block Using this technique an error can be detected if a pointer to a constant is passed to a function where it can be changed char strcpy char dst const char src 4 2 References All arguments are passed to functions by value which means local copies of original arguments are created and a change in a copy does not affect the original The pointer to the variable needs to be passed to the function if the programmers want to change the variable inside the function A certain number of situations exist where we want the same effect without the use of operator amp We refer to passing of large object by reference in order to save time It is possible to declare object in AleC as a reference to another object of known type We will encounter this situation when we declare formal parameters local object and the type of the data that the function returns 4 2 1 Formal references If you declare a formal parameter of a function as a reference the address of the argument will be passed to the function and not the copy of the argument Then every change of the parameter changes the argument Declaration of a reference is the same as in the case of the pointer except we use the operator amp instead of fl int pi pi 2 int amp pi pit f3 int i 1 EL i after return i is still 1 f2 i after return i is 2 2 i i
20. he private members in the base class are inaccessible in the derived class and if the class is inherited as private no member even if declared public is accessible The situation is somewhat better with the class B Member b2 is accessible but b1 is not These restrictions can be circumvented f the members of base classes are declared as protected instead of private This makes them accessible for methods and friends of the derived class only 4 14 2 Access to members in the hierarchy bearing the same name Every class on the inheritance tree has its own area of visibility which enables the appearance of the members and methods of the same name in many places and their mutual masking Access to masked parameters is still possible using the operator of resolution class A int a public void show class B public A int b public void show foo B b b show calls show of class B b B show same b A show show of base class A 4 Object oriented programming 43 4 14 3 Virtual base classes Virtual classes are still not functioning in the current release of Alecsis No class can be repeated in the list of base classes after the character However the same class can appear more than once if it was the base class for more than one base class Class A class B A class C A class D B C idee fe Class A appears twice in D once in B and another time
21. ith the type of the argument since the compiler is not able to perform implicit conversions in this case Note If the parameter to be read using va_arg is of type char or of some other short type the second parameter of va_ arg must be int Note Coma is not necessary in between the last defined parameter and the symbol void print menu const char title Implementation of functions with the variable number of arguments utilizes the fact that all formal parameters of the function are stored in consecutive memory locations However some computers have special alignment rules Computers Silicon Graphics and HP 9000 s700 S00 store parameters of type double on the memory locations that can be divided by 8 This option is implemented in varargs h file you just have to define DWORD_ ALIGNMENT flag before including this file define DWORD ALIGNMENT include lt varargs h gt For other computers where Alecsis until now installed such alignment is not necessary If you install Alecsis on some new type of computer that is not predefined in Makefile you should see the alignment rules for that computer in file usr include varargs h that is used by C You can then adapt Alecsis varargs h to fit your needs 32 Alecsis 2 3 User s manual 4 7 Visibility area resolution operator This operator is the first in the series of operators not used in C This operator two consecutive colons was designed to solve
22. les and consequently frees the space after the area of visibility is closed In order to allow the class object to behave as object of predefined types int double etc we need to define constructors and destructors as separate methods The purpose of the constructor is to allocate memory space for pointers which are members of classes and to initialize them whenever an object of that class is declared Destructor does the reverse it frees the memory occupied by a constructor deinitialization is not necessary Destructor is not necessary for class objects without pointers because there is nothing to free but the constructor is 4 Object oriented programming 37 4 9 1 Constructors Constructor is the method that has the same name as the class Constructor does not return anything but it can have parameters It can be overloaded Constructor needs not to be called explicitly since compiler calls it whenever it creates an object In order to make that happen constructor has to be defined as public class Point int xVal yVal public Point int x int y xVal x yVal y Point xVal yVal 0 void show printf xval d yval d n xVal yVal Arguments are defined in case the constructor has parameters Point pl p2 2 3 p3 p2 Object pl does not have arguments so compiler calls constructor without parameters Object p2 uses constructor with two int type parameters while p3 is initializ
23. ning identically named functions to be called when needed Word operator should be put before the operator name which is the special signal for compiler to transform it into a function name class complex double re im real and imaginary part of complex number public complex double r 0 0 double i 0 0 re r im i friend complex operator complex complex inline complex operator complex 1 complex r return complex l re r re l im r im foo 4 complex cl 2 3 c2 7 8 c3 cl C2 Class complex from this example is a new type of data that represents complex numbers The class constructor defines the number and becomes a complex zero in the case of left out arguments Usually compiler would not know to add two complex numbers and would report an error However operator overloads on the global level if used on two objects of the same type Since the operator function is global it could not access to private members unless previously defined as friendly within the class The function is defined as inline due to its shorth length Object passes to it using shallow copying by value which is satisfactory in this case since they are only 16 bytes long without pointers The temporary object created in the operator function returns to the environment using command return shallow copying Here it initializes object c3 which gets the value of 9 1 11 All operators in AleC can be overload
24. renced outside the function These functions are methods since they define the operations with the objects of the class The access to the members of a class is not simple doe to the need to control the access Members of a class are initialized as private that is no one except their own methods have the right to access them Members and methods have to be defined as public to be accessible We will talk about the third type of access protected in the chapter on inheritance 4 Object oriented programming 33 4 8 2 Declaration and definition of methods Methods declared in a class have to be defined somewhere Shorter methods can be defined within the class which makes them inline functions It is possible to use members of the class not yet declared as in the case of definition outside of class within the methods defined within the class since those methods are not translated until the class is entirely defined Methods defined outside a class can be inline too but the key word has to be used in this case The following is an example of a class class Point int xVal yVal public void set xVal yVal 0 4 void set int x int y xVal x yVal y void show printf xval d yval d n xVal yVal int Xval return xVal int Yval return yVal The class Point has only two data of int type xVal and yVal These are private and cannot be accessed from outside since only class m
25. rformed using implicit conversion into the base class ob 0 draw calling circle draw ob 1 draw calling rectangle draw ob 2 draw calling circle draw ob 3 draw calling rectangle draw If the base class is not abstract then you need to define both the base and the derived implementation of the virtual function
26. ructor for every index of vector vp and then frees the vector 4 14 Inheritance An analysis of a large number of programs and the experience of programmers revealed that the largest portion of time needed for the writing of a new program is spent on the same routines such as functions for list stack tree graph manipulations The mechanism of inheritance is a characteristic of object oriented programming and it uses these functions as building elements of programs The essence of inheritance is that children inherit parents with possible changes In C and AleC the children are derived and the parents are the base classes There is a mono inheritance one base class and multiple inheritance more base classes Since derived classes can be base classes for some other classes the whole system can be very complex as a tree or hierarchy of inheritance similar to a family tree 4 14 1 Inheritance and rules concerning access rights In a declaration of a derived class base classes are listed after the derived class name and the colon class A int al a2 42 Alecsis 2 3 User s manual public int a3 class B int b1 public int b2 class C private A public B int c1 c2 public int c3 Class C is a derived class which inherits characteristics of classes A and B This means that object of class C would be 12 8 12 32 bytes The problem arises with the access rights T
27. ry object generates its own copy of the individual members which occupy different memory locations If we want the present state of object characteristics including number state etc static members can provide the necessary information There exists only one copy of the static member of the class no matter how many copies class objects exist These members are internally implemented as static or global variables and do not affect the size of the class only non static members do Declaration of the static element is not a definition therefore in the case of the class on the global level it is the same as for any other global variable but using access operator class X int a b static s declaration of the static member of the class of int type class occupies 8 bytes int X s 0 definition of the static member of class X Access is the same for static members as for any other member of the class 4 Object oriented programming 35 X s 3 access beyond any object X x object x class X int xs X S access using object x 4 8 4 2 Static methods These functions are defined as methods but are very similar in behaviour to global functions These functions do not accept current class object as a hidden parameter since they are used outside an object so key word this cannot be used with these functions They have to accept a pointer to an object explicitly in order to use it class X int xval p
28. that the function is already defined in the same file using the key word inline before its definition This is used to speed up significantly the execution of the program However certain restrictions apply such as inline functions cannot have any loops or unconditional jump commands cannot declare static variables local yes cannot pass their address cannot be recursive etc They are most useful when working with small but often called functions inline double sum_a_b double a double b return a b 4 6 Functions with variable number of arguments This feature is a part of C and it enables the writing of functions like printf 4 Object oriented programming 31 include lt varargs h gt void print menu const char title char field char args printf menu s options n title va_start args title int nmenu 0 while field va_arg args char 0 printf t d s n nmenu field At least one argument must be given in the list of formal arguments The last given parameter in our example there is only one given parameter title is used as the argument for macro va_start from varags h file Macro va_start sets pointer args to the memory location after the parameter title i e to the memory where the next argument is All other parameters will result from the call of macro va_arg by passing the initialized pointer args and the expected parameter type The type has to agree w
29. ublic Static void fx class X X x object x X fx amp x call of static function independently from the object x x amp Xx classical method of access void X fx X x definition of static fn fx class X xval 1 error which xval is this referring to this xval 1 error as well X gt Xval 2 O K Static member and functions lessen the congestion of the global area with symbols help define which global or static symbols belong to which class and offer the ability to limit the access using private keyword 4 8 5 Class friends One may need that other functions not only the class methods are allowed access the private members of the class To enable that one may declare functions or classes as friends 4 8 5 1 Friendly functions A function can be defined as a friend of the class by using the key word friend A friendly function has the right of access to private members of the class class Y incomplete Y class declaration class X int xval yval public set int x int y xval x yval y friend int f1 X global function f1 is a friend 36 Alecsis 2 3 User s manual friend Y fy X method fy of class Y is a friend i class Y ending of class Y declaration int Yy public fy X int f1 X x return x gt xval x gt yval definition f1 Y fy X x return x gt xval x gt yval definition Y fy
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