How to loop through a va_list if the number of arguments is unknown?

Question

How do I loop through a va_list if the number of additional arguments is unknown?

#include 
#include 

int add(int x, int y, ...         


        

Answer 1

You use the first argument to indicate the number of elements, and then, you can pass any number of elements to the function.

Here is a typical call:

int i = add(5, 20, 30, 40, 50, 60);

There are 5 numbers to sum, so the first parameter is 5. Then the rest are the 5 numbers to add up.

The function would then be:

int add(int argc, ...)
{
    int result = 0;
    va_list ptr;
    va_start(ptr, argc);

    for (int i = 0; i < argc; i++)
    {
        result += va_arg(ptr, int);
    }
    return result;
}

References:

va_arg()

va_start()

va_list()