[C]我可以使用比参数更大的类型调用va_arg，然后强制转换值吗？

Question

I wonder if this is valid code:

int a(va_list args, int is_int, ...)
{
    long long n = va_arg(args, long long);
    return (is_int ? ((int)n) : n);
}
void b(va_list args)
{
    int x = -100;
    a(args, 1, x);
}

I've written some unnecessary complicated code, I've made mistakes, and I feel like this is the simplest way to fix what I did without rewriting the whole thing, but I don't know if this can cause errors(or segfaults, or something else).

Answer 1

No, and the issue is not just limited to size. If the types mismatch, the behavior of your whole program is undefined. There are some very limited exceptions like signedness mismatch when the actual value passed fits in either signedness.