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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__ >= 2     #  define __func__ __FUNCTION__     # else     #  define __func__ "
     
      "     # endif     #endifIn 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 (0);       return 0;     }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.