Variadic macros with 0 arguments in C99

Question

I have some debugging code that looks like the following:

#define STRINGIFY(x) #x
#define TOSTRING(x) STRINGIFY(x)
#define AT __FILE__ \":\" TOSTRING(__LINE__)
v         


        

Answer 1

I see two solutions to this problem. (Three if you count 'stick with gcc').

Extra special case macro

Add a new macro for when you want to print a fixed string.

#define my_errorf(str) my_error(str, NULL)

Pro: Minimum amount of extra code.
Con: It's easy to use the wrong macro (but at least you notice this at compile time).

Put fmt inside the '...'

Vararg macro's can have only __VA_ARGS__ as parameter (unlike vararg functions). So you can put the fmt argument inside the __VA_ARGS__ and change your function.

void __my_error(const char *loc, ...);
#define my_error(...) __my_error(AT, __VA_ARGS__)

Pro: One syntax/macro for all error messages.
Con: Requires rewriting of your __my_error function, which might not be possible.