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

				// Build don't link:				// 				// Copyright (C) 2001 Free Software Foundation, Inc.				// Contributed by Nathan Sidwell 22 May 2001 								// Bug 2184. Using decls in templates weren't doing the right thing.								namespace N {				  template 				  class vector {};				}								void g(const int&) {				  using N::vector;				  typedef vector V;				}								template 				void f(const J&) {				  using N::vector;				  typedef vector V;				}								int main() {				  f(0);				}