Question

I have a function A(...) and B(...). Now I have to call B inside A, any methods to pass that ... from A into B? Pseudocode:

void A(...)
{
   // Some operators
   B(...); // Instead of ... I need to pass A's args
}

p.s. I know this could be done using macros but what about functions.

Answer 1

You can’t forward va_args. You can only forward va_list.

void vB(int first, va_list ap)
{
   // do stuff with ap.
}

void B(int first, ...)
{
   va_list ap;
   va_start(ap, first);
   vB(first, ap);
   va_end(ap);
}

void A(int something_else, int first, ...)
{
   va_list ap;
   va_start(ap, first);
   vB(first, ap);       // <-- call vB instead of B.
   va_end(ap);
}

(This is also why functions like vprintf exists.)

---

If you are using C++11, you could do this with variadic templates with perfect forwarding:

template <typename... T>
void A(T&&... args)
{
    B(std::forward<T>(args)...);
}