Variadic macro extensions

Variadic macro extensions refer to two extensions to C99 and Standard C++ related to macros with variable number of arguments. One extension is a mechanism for renaming the variable argument identifier from __VA_ARGS__ to a user-defined identifier. The other extension provides a way to remove the dangling comma in a variadic macro when no variable arguments are specified.

The following examples demonstrate the use of an identifier in place of __VA_ARGS__. The first definition of the macro debug exemplifies the usual usage of __VA_ARGS__. The second definition shows the use of the identifier args in place of __VA_ARGS__.

#define debug1(format, …)  printf(format, ## __VA_ARGS__)
#define debug2(format, args …)  printf(format, ## args)

Invocation	Result of macro expansion
`debug1("Hello %s\n","World");`	`printf("Hello %s\n","World");`
`debug2("Hello %s\n","World");`	`printf("Hello %s\n","World");`

The preprocessor removes the trailing comma if the variable arguments to a function macro are omitted or empty and the comma followed by ## precedes the variable argument identifier in the function macro definition.

C++0x Beginning of C++0x only.

In C++0x, the variadic macros feature and changes concerning empty macro arguments are adopted from the C99 preprocessor to provide a common preprocessor interface for C and C++ compilers. Variadic macros and empty macro arguments are supported in C++0x. For more information, see C99 preprocessor features adopted in C++0x.

C++0x End of C++0x only.