5.40 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 initializechar
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.