Ihandle *CiupVbox (Ihandle *first, ...)
{
  Ihandle *box;
  va_list arg
  va_start (arg, first);
  box = IupVbox (first, arg);
  return box;
}

... later in code ...

... Version 1
Ihandle *mainBox = CiupVbox (IupLabel ("Hello"), IupLabel ("World"), NULL); // fails, seg fault

... Version 2
Ihandle *mainBox = IupVbox (IupLabel ("Hello"), IupLabel ("World"), NULL); // Works fine