gcc-you can use this code to learn something about gcc, and inquire further into linux,

				// Test that built-in functions are recognized with a prototype.				// Origin: Roger Sayle  Mar 20, 2002				// Copyright (C) 2002 Free Software Foundation.				//				// Special g++ Options: -O2								extern "C" void link_error (void);								namespace std {				typedef __SIZE_TYPE__ size_t;				extern "C" size_t strlen (const char*);				}								int				main ()				{				  if (std::strlen ("foo") != 3)				    link_error ();				  return 0;				}