From owner-freebsd-hackers  Fri Mar 30  8:22: 3 2001
Delivered-To: freebsd-hackers@freebsd.org
Received: from vieo.com (vieo.com [216.30.79.131])
	by hub.freebsd.org (Postfix) with ESMTP id 6A3C237B71C
	for <freebsd-hackers@FreeBSD.ORG>; Fri, 30 Mar 2001 08:21:59 -0800 (PST)
	(envelope-from johng@vieo.com)
Received: (from johng@localhost)
	by vieo.com (8.11.2/8.11.2) id f2UGLwY45837;
	Fri, 30 Mar 2001 10:21:58 -0600 (CST)
	(envelope-from johng)
Date: Fri, 30 Mar 2001 10:21:58 -0600 (CST)
From: John Gregor <johng@vieo.com>
Message-Id: <200103301621.f2UGLwY45837@vieo.com>
To: freebsd-hackers@FreeBSD.ORG, tech-kern@netbsd.org
Subject: Re: Question regarding the array of size 0.
In-Reply-To: <3AC4AE65.8C4D9482@theseventhson.freeserve.co.uk>
Sender: owner-freebsd-hackers@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

Lord Isildur wrote:
> 
> sine one knows the size of the struct, who need the pointer? just
> take the displacement.
> 
> char* buf; /* some buffer */
> struct foo{
> int header;
> struct funkystruct blah;
> };
> 
> (struct foo*)buf; /*your headers are here */
> (struct foo*)buf+1; /* and your data is here */

The only problem is that:

struct foo {				(struct foo*)buf;
    int count;		- and -		(struct foo*)buf+1;
    short flags;
    char data[0];
};

will have different alignments.  If what you want is for data[] to
begin immediately after flags, buf+1 doesn't work.

Oh, and as to the data[] vs data[0] problem, one can always do the
equivalent of:

#if defined(C99STUBS)
#	define ARRAYSTUB(x) x[0]
#elif defined(GCCSTUBS)
#	define ARRAYSTUB(x) x[]
#endif

struct foo {
    int			 count;
    short		 flags;
    char       ARRAYSTUB(data);
};

-JohnG

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message