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 (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.
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