C Preprocessor Remove Trailing Comma

Question

I have a macro like this:

#define C( a... ) ( char *[] ){ a, 0 }

This works for non-empty arguments:

C( \"a\", \"b\" ) => (          


        

Answer 1

Check out GCC's __VA_OPT__() function macro that can be used within a variadic macro.

#define C(...) (char *[]) { __VA_ARGS__ __VA_OPT__(,) 0 }

C("a", "b");   expands to (char *[]) { "a", "b" , 0 };
C();           expands to (char *[]) { 0 };

The arguments passed to __VA_OPT__() will only be expanded if __VA_ARGS__ is non-empty.