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From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.std.c
Subject: Re: Passing a `va_list *'
Message-ID: <11439@smoke.BRL.MIL>
Date: 28 Oct 89 05:56:13 GMT
References: <MCGRATH.89Oct27150426@tully.Berkeley.EDU>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 27

In article <MCGRATH.89Oct27150426@tully.Berkeley.EDU> mcgrath@tully.Berkeley.EDU (Roland McGrath) writes:
>#include <stddef.h>

That should be <stdarg.h>, of course.

>  va_list args;
>  ack(&args);
...
>void ack(va_list *args)
>{
>  blip(va_arg(args, int **));
>}

I wonder how this could possibly have worked.  va_arg() takes a va_list
as its first argument, not a va_list*.  Let's assume this is a typo.

I don't have my copy of the Standard at hand at the moment, but I did
spend a lot of time working in this area, and as I recall the Standard
guarantees that you can pass the va_list to a function and continue to
use it within the function, but not necessarily a pointer to the va_list.
Upon return from the function, the va_list is "dead" until va_end()ed
and re-va_start()ed.

To answer the question of whether you can use a pointer to the va_list,
you need to consider what types are allowed for va_list.  I don't recall
exactly how this ended up; it changed around a few times.  The one to
watch out for is an array type.