Question

I have zillions of my_printf() function calls in a huge program. I now want to convert them all so that the function takes a new integer argument (call it x) without having to edit the zillions of calls. If my_printf only ever took exactly one string argument then I could do something like this:

    #define my_printf(str) _my_printf(x,str)

    void _my_printf(int x,char *str) // changed from my_printf(char *str)
    {
        // stuff
    }

But as my_printf takes a variable number of arguments I’m not sure how to do it. Can it be done?

EDIT: for those wondering why I should want to do such a thing, here’s a related example:

#if BELT_AND_BRACES_DIAGNOSTIC_MODE
    #define function(x) _function(__FILE__,__LINE__,x)
#else // speed critical optimised mode
    #define function(x) _function(x)
#endif

#if BELT_AND_BRACES_DIAGNOSTIC_MODE
    void _function(char *file,int line,int x)
#else
    void _function(int x)
#endif
{
    // stuff
    #if BELT_AND_BRACES_DIAGNOSTIC_MODE
    if (something_went_wrong)
    {
        printf("Cock up in function when called from %s line %d\n",file,line);
    }
    #endif
}

Answer 1

You may use C99 variadic macros:

#define my_printf(...) my_printf_(x, __VA_ARGS__)

As Microsoft’s implementation suppresse trailing commas, the str argument can be added explicitly

#define my_printf(str, ...) my_printf_(x, str, __VA_ARGS__)

but this would lead to a syntax error in standard C when invoked without variadic arguments

my_printf("foo")

or an empty argument list

my_printf("foo",)

Therefore, I’d go with the first version.