c++ - Class Member Functions and Classes as Friends -

i've written 2 classes: function of first class cannot access private member of second class though function friend second class. found example msdn.microsoft.com there still error: cannot access private member declared in class b

here code msdn:

class b; class { public:     int func1(b& b);  private:     int func2(b& b); };  class b { private:     int _b;      // a::func1 friend function class b     // a::func1 has access members of b     friend int a::func1(b&); };  int a::func1(b& b) { return b._b; }//the same error 1 below here int a::func2(b& b) { return b._b; }   

when write class a friend b there no error want have function want friend class b not whole class a

is compiler fault or code wrong?

i added declaration class b(called forward declaration of class) @ top , compiles. need declare class b before use parameter in member functions of class a.

here code ->

#include<iostream>  class b;  class { public:     int func1(b& b);  private:     int func2(b& b); };  class b { private:     int _b;       // a::func1 friend function class b     // a::func1 has access members of b     friend int a::func1(b&); };  int a::func1(b& b) { return b._b; }//the same error 1 below    here //int a::func2(b& b) { return b._b; }   int main(void){ return 0; } 

if error still persists maybe compiler @ fault.