How to use va_arg to modify the value of a variadic parameter

Question

#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>

void tag_log(const char *format, ...) {
    va_list ap;
    va_start(ap, format);
    for (int i = 0; i < 4; i++) {
        va_arg(ap, int) += 100; // is wrong?
    }
    va_end(ap);
    va_start(ap, format);
    vprintf(format, ap);
    va_end(ap);
}

int main() {
    tag_log("%d, %d, %d, %d\n", 1, 2, 3, 4);
}

Answer 1

va_arg(ap, int) = 100; \/\/ is wrong?<\/code>

<\/blockquote>

Yes, it's wrong. va_arg<\/code> returns an rvalue (which isn't assignable).