6.41. Function Names as Strings
GCC provides three magic variables which 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__ "<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 (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.
