GCC provides three magic variables that hold the name of the current function, as a string. The first of these is __func__, which is part of the C99 standard:

The identifier __func__ is implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declaration

     static const char __func__[] = "function-name";

appeared, where function-name is the name of the lexically-enclosing function. This name is the unadorned name of the function.

__FUNCTION__ is another name for __func__. Older versions of GCC recognize only this name. However, it is not standardized. For maximum portability, we recommend you use __func__, but provide a fallback definition with the preprocessor:

     #if __STDC_VERSION__ < 199901L

     # if __GNUC__ >=

     #  define __func__ __FUNCTION__

     # else

     #  define __func__ "<unknown>"

     # endif

     #endif

In C, __PRETTY_FUNCTION__ is yet another name for __func__. However, in C++, __PRETTY_FUNCTION__ contains the type signature of the function as well as its bare name. For example, this program:

     extern "C" {

     extern int printf (char *, ...);

     }

     class a {

      public:

       void sub (int i)

         {

           printf ("__FUNCTION__ = %s\n", __FUNCTION__);

           printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);

         }

     };

     int

     main (void)

     {

       a ax;

       ax.sub ();

       return ;

     }

gives this output:

     __FUNCTION__ = sub

     __PRETTY_FUNCTION__ = void a::sub(int)

These identifiers are not preprocessor macros. In GCC 3.3 and earlier, in C only, __FUNCTION__ and __PRETTY_FUNCTION__ were treated as string literals; they could be used to initialize char arrays, and they could be concatenated with other string literals. GCC 3.4 and later treat them as variables, like __func__. In C++, __FUNCTION__ and __PRETTY_FUNCTION__ have always been variables.