What's the difference between __PRETTY_FUNCTION__
, __FUNCTION__
, __func__
, and where are they documented? How do I decide which one to use?
__func__
is an implicitly declared identifier that expands to a character array variable containing the function name when it is used inside of a function. It was added to C in C99. From C99 §6.4.2.2/1:
The identifier
__func__
is implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declarationstatic 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.
Note that it is not a macro and it has no special meaning during preprocessing.
__func__
was added to C++ in C++11, where it is specified as containing "an implementation-defined string" (C++11 §8.4.1[dcl.fct.def.general]/8), which is not quite as useful as the specification in C. (The original proposal to add __func__
to C++ was N1642).
__FUNCTION__
is a pre-standard extension that some C compilers support (including gcc and Visual C++); in general, you should use __func__
where it is supported and only use __FUNCTION__
if you are using a compiler that does not support it (for example, Visual C++, which does not support C99 and does not yet support all of C++0x, does not provide __func__
).
__PRETTY_FUNCTION__
is a gcc extension that is mostly the same as __FUNCTION__
, except that for C++ functions it contains the "pretty" name of the function including the signature of the function. Visual C++ has a similar (but not quite identical) extension, __FUNCSIG__
.
For the nonstandard macros, you will want to consult your compiler's documentation. The Visual C++ extensions are included in the MSDN documentation of the C++ compiler's "Predefined Macros". The gcc documentation extensions are described in the gcc documentation page "Function Names as Strings."