Variable Arity in C?

Question

Does anyone knows how I might be able to implement variable arity for functions in C?

For example, a summing function:

Sum(1,2,3,4...); (Takes in a variable

Answer 1

A variable parameter list of ints. Adjust type as necessary:

#include 

void myfunc(int firstarg, ...)
{
    va_list v;
    int i = firstarg;

    va_start(v, firstarg);
    while(i != -1)
    {
        // do things
        i = va_arg(v, int);
    }

    va_end(v);
}

You must be able to determine when to stop reading the variable args. This is done with a terminator argument (-1 in my example), or by knowing the expected number of args from some other source (for example, by examining a formatting string as in printf).