Function Names as Strings

GNU CC predefines two string variables to be the name of the current function. The variable __FUNCTION__ is the name of the function as it appears in the source. The variable __PRETTY_FUNCTION__ is the name of the function pretty printed in a language specific fashion.

These names are always the same in a C function, but in a C++ function they may be different. For example, this program:

extern "C" {
extern int printf (char *, ...);
}

class a {
 public:
  sub (int i)
    {
      printf ("__FUNCTION__ = %s\n", __FUNCTION__);
      printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
    }
};

int
main (void)
{
  a ax;
  ax.sub (0);
  return 0;
}

gives this output:

__FUNCTION__ = sub
__PRETTY_FUNCTION__ = int  a::sub (int)

These names are not macros: they are predefined string variables. For example, `#ifdef __FUNCTION__' does not have any special meaning inside a function, since the preprocessor does not do anything special with the identifier __FUNCTION__.