Understanding Friend Classes and Functions in C++

1. Friend Class

2. Friend Class Like friend function a class can also be declared as friend of other class. When a class is created as friend class then all the member functions of the friend class also become the friend of the other class. This requires the condition that the friend becoming class must be first declared or defined (forward declaration). Similarly like, friend function. A class can be made a friend of another class using keyword friend.

3. Friend Class For example: class A { friend class B; // class B is a friend class ..... ..... ..... }; class B{ ..... ..... ..... }; When a class is made as friend class, all the member functions of that class becomes friend function. In this program, all member functions of class B will be friend function of class A. Thus, any member function of class B can access the private and protected data of class A.

4. Friend Class If B is declared friend class of A then, all member functions of class B can access private data and protected data of class A.

5. Friend Class class A { int a; public: friend class B; void changea() {a=10;cout<<"value in A"<<a;} }; class B { public: void changeb(A x) {x.a=100;cout<<"\nValue in B"<<x.a;} }; void main() { A obj1; obj1.changea(); B obj2; obj2.changeb(obj1); }