Friend Function - Use Cases

Use Cases

This approach may be used when a function needs to access private data in objects from two different classes. This may be accomplished in two similar ways

  • a function of global or namespace scope may be declared as friend of both classes
  • a member function of one class may be declared as friend of another one.
#include using namespace std; class B; // Forward declaration of class B in order for example to compile. class A { private: int a; public: A { a = 0; } void show(A& x, B& y); friend void ::show(A& x, B& y); // declaration of global friend }; class B { private: int b; public: B { b = 6; } friend void ::show(A& x, B& y); // declaration of global friend friend void A::show(A& x, B& y); // declaration of friend from other class }; // Definition of a member function of A; this member is a friend of B void A::show(A& x, B& y) { cout << "Show via function member of A" << endl; cout << "A::a = " << x.a << endl; cout << "B::b = " << y.b << endl; } // Friend for A and B, definition of global function void show(A& x, B& y) { cout << "Show via global function" << endl; cout << "A::a = " << x.a << endl; cout << "B::b = " << y.b << endl; } int main { A a; B b; show(a,b); a.show(a,b); }

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