this is a gcc file, you can download it and learn its usetility, for further detail please look at t

				// Build don't link:								class A				{				protected:				  int i;     				};								class B : private A				{				protected:				  A::i;				};								struct C : public B {				  friend int f(C *p);				};								int f(C *p) {				  return p->i;				}