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4.38 Function Names as Strings

GNU CC predefines two string variables to be the name of the current function. The variable __FUNCTION__ is the name of the function as it appears in the source. The variable __PRETTY_FUNCTION__ is the name of the function pretty printed in a language specific fashion.

These names are always the same in a C function, but in a C++ function they may be different. For example, this program:

extern "C" { extern int printf (char *, ...); } class a { public: 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__ = int a::sub (int)

These names are not macros: they are predefined string variables. For example, `#ifdef __FUNCTION__' does not have any special meaning inside a function, since the preprocessor does not do anything special with the identifier __FUNCTION__.