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

				// Test that default args don't mess up pmf type comparisons.				// Contributed by Jason Merrill .								struct A {				  void f (int = 0) { }				};								int				main ()				{				  void (A::*p)(int) = 0;				  p = &A::f;				  if (p != &A::f)				    return 1;				}