Function Names as Strings#
GCC provides three magic constants that hold the name of the current
function as a string. In C++11 and later modes, all three are treated
as constant expressions and can be used in constexpr
constexts.
The first of these constants 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. As an
extension, at file (or, in C++, namespace scope), __func__
evaluates to the empty string.
__FUNCTION__
is another name for __func__
, provided for
backward compatibility with old versions of GCC.
In C, __PRETTY_FUNCTION__
is yet another name for
__func__
, except that at file scope (or, in C++, namespace scope),
it evaluates to the string "top level"
. In addition, in C++,
__PRETTY_FUNCTION__
contains the signature of the function as
well as its bare name. For example, this program:
extern "C" int printf (const 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 variables, not preprocessor macros, and may not
be used to initialize char
arrays or be concatenated with string
literals.