Question

I have a function that takes 3 arguments. a vector of other functions, a void*, and an arbitrary list of arguments. The function is designed to pass in it’s void* and arbitrary list of arguments to each function in the list, which the functions will handle themselves. here is an example of what I want:

typedef void (*fptr)(const void* userdata, ...);

void execute_all(vector<fptr> funcs, void* userdata, ...){
    for (int i = 0;i<funcs.size();i++){
        fptr func = funcs[i];
        //execute func with userdata and ... from above.
        //like (*func)(userdata, ...); which obviously doesnt work
    }
}

I need to know how to forward all arguments into each function. Dont worry about ensuring compatibility. I handle that elsewhere.

Thanks

Answer 1

You can’t directly pass down variadic arguments from a variadic function to another variadic function. However, you can make the called (inner) function accept a va_list, then pass that list around:

#include <cstdarg>

void callee(void *first, va_list args);

void caller(void *first, ...)
{
    va_list args;
    va_start(args, first);
    callee(first, args);
    va_end(args);
}