Predefined Macros for function name func

Question

I am attempting to build a debug log message function that records the file, line, and function of of where the log message was called from.

#define DEBUG_PANIC(p) CLogging::Debuglogf( "Debug marker (%s) - ::%s() in file: %s(%d)", p, __func__ , __FILE__, __LINE__ );

The above code works on some compilers but not all. My code needs to be cross compatible with GCC as well as Microsoft Visual studios. I have added the below defines to help with compatibility.

#ifndef __FUNCTION_NAME__
    #if defined __func__ 
        // Undeclared 
        #define __FUNCTION_NAME__   __func__ 
    #elif defined __FUNCTION__ 
        // Undeclared
        #define __FUNCTION_NAME__   __FUNCTION__  
    #elif defined __PRETTY_FUNCTION__
        // Undeclared
        #define __FUNCTION_NAME__   __PRETTY_FUNCTION__
    #else
        // Declared
        #define __FUNCTION_NAME__   "N/A"   
    #endif // __func__ 

#endif // __FUNCTION_NAME__

#define DEBUG_PANIC(p) CLogging::Debuglogf( "Debug marker (%s) - ::%s() in file: %s(%d)", p, __FUNCTION_NAME__, __FILE__, __LINE__ );

The problem with the above code snippet is that it is the #else macro is active on all compilers while the other macros are not. in other words #if defined __func__ is false on compilers where __func__ is a predefined macro.

My question is

How do I create a cross compiler macro to find the function name ?
How can I tell if a __func__ can be used?

@KeithThompson Sorry I forgot to add that to the question, Yes C++ — Steven Smethurst, Mar 09 '13 at 00:28
related: [What's the difference between `__PRETTY_FUNCTION__`, `__FUNCTION__`, `__func__`?](https://stackoverflow.com/questions/4384765/whats-the-difference-between-pretty-function-function-func). — Ciro Santilli OurBigBook.com, Apr 26 '19 at 10:11

score 43 · Accepted Answer · answered Mar 08 '13 at 23:55

43

You're assuming __func__ is a macro, but it's not. It's a conditionally-supported predefined identifier, so you can't check it with #if defined or #ifdef.

If the compilers have no way of telling you whether this is supported (they could via a _FUNC_SUPPORTED or something, I'm not saying they actually are doing this), you'll have to check the compiler instead of the actual identifier.

Something along the lines:

#ifndef __FUNCTION_NAME__
    #ifdef WIN32   //WINDOWS
        #define __FUNCTION_NAME__   __FUNCTION__  
    #else          //*NIX
        #define __FUNCTION_NAME__   __func__ 
    #endif
#endif

answered Mar 08 '13 at 23:55

Luchian Grigore

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Any C compiler conforming to C99 or later *must* support `__func__`; in that sense, it's not an optional feature. So one way to tell that `__func__` is supported is by checking `__STDC_VERSION__ >= 199901L`. (Though a pre-C99 or non-conforming compiler could support it as an extension.) – Keith Thompson Mar 08 '13 at 23:59
5

@KeithThompson I was assuming C++. But the main point was that it's not a macro. – Luchian Grigore Mar 09 '13 at 00:00
6

Ah, good point; the OP didn't add a tag for the language. The C++ standard didn't mandate `__func__` until 2011. It's probably a common extension for pre-C++11 compilers. – Keith Thompson Mar 09 '13 at 00:04

score 17 · Answer 2 · answered Jun 30 '15 at 11:22

17

As often Boost is THE cross platform solution with BOOST_CURRENT_FUNCTION defined in <boost/current_function.hpp>.

answered Jun 30 '15 at 11:22

Jean Davy

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score 11 · Answer 3 · answered Jan 06 '16 at 22:47

I would like to add that the __FUNCTION__ macro is defined for both GCC and MSVC. Though non-standard, it is available on both compilers.

GCC Standard Predefined Macros quote:

C99 introduces __func__, and GCC has provided __FUNCTION__ for a long time. Both of these are strings containing the name of the current function (there are slight semantic differences; see the GCC manual). Neither of them is a macro; the preprocessor does not know the name of the current function. They tend to be useful in conjunction with __FILE__ and __LINE__, though.

MSVC Predefined Macros quote:

__FUNCTION__

Valid only in a function. Defines the undecorated name of the enclosing function as a string literal.

__FUNCTION__ is not expanded if you use the /EP or /P compiler option.

See __FUNCDNAME__ for an example.

So using __FUNCTION__ would be ok, since both compilers implement it. Though you may not get the same results on both compilers but that might be acceptable in some situations.

_I would like to add that the `__FUNCTION__` macro is defined for both GCC and MSVC._ the documentation quote explicitly states that this is **not** a macro. — Antonin Décimo, Apr 12 '20 at 09:38

score 7 · Answer 4 · edited May 23 '17 at 12:01

they are neither preprocessor macros, like __FILE__ and __LINE__, nor variables.

Taken from the following link:

http://gcc.gnu.org/onlinedocs/gcc-3.2/gcc/Function-Names.html

Also, please check out this other question that was answered that is similar to yours:

How to check if __PRETTY_FUNCTION__ can be used?

Example:

#ifdef _MSC_VER // Visual Studio
    #define FUNCTION_NAME __FUNCTION__
#endif

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