C + + Development Series-friend function friend class

Friend function

The private properties of a default class can only be accessed directly within the class.友元函数申明在内的内部，实现在类的外部可以直接访问类的私有属性。

classa1{ Public: A1 () {a1 = -; A2 = $; }intGetA1 () {return  This->a1; }//Declare a friend function    friend voidSetA1 (A1 *p,intA1);//This function is a good friend of this class    protected:Private:intA1;intA2;};voidSetA1 (A1 *p,intA1) {p->a1 = A1;}voidMain () {A1 mya1;     Cout<<mya1.geta1 () <<endl; SetA1 (&AMP;MYA1, -);//Modify private properties of Class A with friend functionCout<<mya1.geta1 () <<endl; System"Pause");}

Add:

• The Friend function declaration statement location is independent of private and public.
• A friend function typically has parameters for that object, access private member property data through an object parameter

Friend class

• If Class B is a friend class of Class A, all member functions of Class B are friend functions of Class A
• A friend class is typically designed as an auxiliary class for passing messages between data operations or classes

C + + Development Series-friend function friend class