Visual studio __VA_ARGS__ issue

c++, c-preprocessor, variadic-functions, variadic-macros, visual-studio-2010

Solution

Yes, this is a longstanding bug in the Visual C++ preprocessor. To work around it, use indirection:

#define INDIRECT_EXPAND(m, args) m args

#define FiltedLog( ...) \
    if (logDetail) \
        INDIRECT_EXPAND(MP_LOG, (LOG_INFO, __VA_ARGS__));

(Do note that `__PRETTY_FUNCTION__` is a nonstandard extension that is not supported by Visual C++.)

Problem

I run cl /P test.cpp, the file and result is as following. test.cpp ``` #define FiltedLog( ...) \ if (logDetail) \ MP_LOG(LOG_INFO, __VA_ARGS__); #define MP_LOG(level,fmt,...) \ BOOAT::LOG("MP", level, fmt, ##__VA_ARGS__) #define LOG(tag,level,fmt,...) \ Log::log(tag, level, "%s: " fmt, __PRETTY_FUNCTION__, ##__VA_ARGS__) int main () { FiltedLog ( "abc", 1, 2); } ``` Cl /P test.cpp : ``` #line 1 "test.cpp" int main () { if (logDetail) BOOAT::Log::log("MP", LOG_INFO, "%s: " "abc", 1, 2, __PRETTY_FUNCTION__ );; } ``` I wonder why the `__PRETTY_FUNCTION__` are put as the last arguments in the result. I assume the result should be: ``` if (logDetail) BOOAT::Log::log("MP", LOG_INFO, "%s: " "abc", __PRETTY_FUNCTION__, 1, 2);; ``` Is it an bug of VS 2010?

Original source