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

				// Build don't link: 				// GROUPS passed access				// access file				// From: Jeffrey C. Gealow 				// Date:     Thu, 18 Feb 93 10:22:23 -0500				// Subject:  nested class access control bug				// Message-ID: 												class enclose {				public:				  class nested_public { int x; };				protected:				  class nested_protected { int x; };				private:				  class nested_private { int x; }; // ERROR - private				};								class derived : public enclose {				  nested_public obj1;     // ok				  nested_protected obj2;  // ok				  nested_private obj3;    // error// ERROR - in this context				};