Re: second parameter of `va_start' not last named argument

[Antonio Coralles <noche dot suapie at reflex dot at>]

Ian Lance Taylor wrote:

> Antonio Coralles <noche.suapie@reflex.at <mailto:>> writes:
>
> > is there a way to prevent this gcc warning?
> > in a code similar to
> >
> > void foo(const std::string& format, ...);
> >
> > i determine the neccessary number of arguments by counting the
> > occurences of "%s" in format,
> > similar to printf. therefore, there is no need for the caller to pass
> > the number of arguments as a second
> > argument.
>
> If you want help, you will need to post a complete test case.
> Specifically, how are you calling va_start?  When you call va_start,
> you must pass it the last named argument in the function.  Any other
> usage is invalid.
>
> Ian

Here is a test case:

the source looks like this:

void foo(const std::string& format, ...)
{
   unsigned num = string_count("%s", format); // counts how often "%s"
   occurs in format
   va_list p_arg;
   va_start(p_arg, num);
   for(; num > 0; --num)
   {
      const char* arg = va_arg(p_arg, const char*)
      // ... do something with the acquired string
   }
   // ...
}

as i said, the function works similar to printf, and in printf there's no
second parameter specifying the length of the argument list...

antonio