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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, like the following 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;
    }

The program, then, gives the following 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__.