Function Names as Strings

【Function Names as Strings】

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(old):

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（GCC2.0以上版本没有__func__，只有__FUNCTION__，2.0以下版本编译器不认识__FUNCTION__）. However, it is not standardized. For maximum portability, we recommend you use __func__, but provide a fallback definition with the preprocessor（GCC2.0）（通过以下的宏使用__func__可以提供跨版本特性）:

     #if __STDC_VERSION__ < 199901L
     # if __GNUC__ >= 2
     #  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（C++中__PRETTY_FUNCTION__包含函数签名）. For example, this program:

     extern "C" {
     extern int printf (char *, ...);
     }
     
     class a {
      public:
       void sub (int i)
         {
           printf ("__FUNCTION__ = %s
", __FUNCTION__);
           printf ("__PRETTY_FUNCTION__ = %s
", __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__（GCC3.4以后版本，此2种东西均为变量）. In C++, __FUNCTION__ and__PRETTY_FUNCTION__ have always been variables.

  参考：http://gcc.gnu.org/onlinedocs/gcc/Function-Names.html#Function-Names