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 C {				public:				  virtual void f();				};								extern volatile C* cp;				extern volatile C& cr;								void f ()				{				  dynamic_cast(cp); // ERROR - cannot dynamic_cast				  dynamic_cast(cr); // ERROR - cannot dynamic_cast				}