问题
For debugbuilds, I usually use Clang, as it formats warnings and errors better, and makes it a little easier to track them down, and fix them.
But recently after adding a Macro with variadic arguments, Clang told me the following (from a dummy project):
main.cpp:5:20: warning: named variadic macros are a GNU extension [-Wvariadic-macros]
#define stuff3(args...) stuff_i(args)
I know that macroname(args...) compiles fine in a wide range of compilers, including Visualstudio, Sunstudio, and of course GCC. But just to make sure that clang is right, I tried two other ways of expanding the variadic arguments:
Number 1:
#define stuff1(...) stuff_i(...)
Number 2:
#define stuff2(...) stuff_i(__VA_ARGS__)
On both I receive this message:
main.cpp:3:16: warning: variadic macros were introduced in C99 [-Wvariadic-macros]
... Which makes me wonder if Variadic macros are actually part of the standard of C++ (and of course I know that the Preprocessor is interpreted independently)?
回答1:
Quote Wikipedia:
Variable-argument macros were introduced in 1999 in the ISO/IEC 9899:1999 (C99) revision of the C language standard, and in 2011 in ISO/IEC 14882:2011 (C++11) revision of the C++ language standard.
So it's standard from C99 and C++11 onwards, but a GNU extension in C++03.
回答2:
As of C++11, variadic macros are now included in standard C++. Section 16.3 of the C++11 standard specifies variadic macros such that they are compatible with variadic macros from C99 (the second form in the question).
Here is an example of a standard-conforming variadic macro definition in C++:
#define foo(x, y, ...) bar(x, y, __VA_ARGS__)
回答3:
In the form of your example "Number 2", they are standard in C99, and generally a C++ compiler's preprocessor is the same for C and C++ compilation.
They are also supported Microsoft VC++ despite its otherwise stubborn resistance to C99 compliance. So between that and GCC there are few reasons to avoid using them. Even on most embedded systems compilers I use they are supported.
Avoid the "Number 1" form however, that is firmly GCC specific, and no doubt deprecated.
回答4:
Standard says in 16.3 Macro replacement:
The identifier _ _ VA_ARGS _ _ shall occur only in the replacement-list of a function-like macro that uses the ellipsis notation in the parameters.
来源：https://stackoverflow.com/questions/4786649/are-variadic-macros-nonstandard