creating va_list dynamically in GCC - can it be done?

Question

my problem with vsprintf is that I can not obtain input arguments directly, I have to first get inputs one by one and save them in void**, then pas

Answer 1

If the problem you're trying to solve is inserting passing arbitrary types to a function in va_list style, then, consider using union:

#include 
#include 

union ARG
{
    int d;
    char* s;
    double f;
};

int main()
{
    printf("%d %s %f \n", 1, "two", 3.1415 );
    // Output: 1 two 3.141500

    char format[ 1024 ] = "%d %s %f\n";
    ARG args[ 5 ] = { };
    args[ 0 ].d = 1;
    args[ 1 ].s = "two";
    args[ 2 ].f = 3.1415;
    printf( format, args[ 0 ], args[ 1 ], args[ 2 ], args[ 3 ], args[ 4 ] );
    // Output: 1 two 3.141500

    return 0;
}

Some things you'll note about my solution:

• No attempt is made to produce the correct number of arguments. i.e. I oversupply the arguments, but, most functions will look at the first parameter to determine how to handle the rest (i.e. format)
• I didn't bother dynamically create the format, but, it is a trivial exercise to build a routine that dynamically populates format and args.

Tested this on: - Ubuntu, g++ - Android NDK

I did some more testing, and, confirmed @PeterCoordes comments about this answer not working for double precision.