Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!paperboy!osf.org!dbrooks
From: dbrooks@osf.org (David Brooks)
Newsgroups: comp.lang.c
Subject: Re: finding offset of a member in C structures
Message-ID: <22103@paperboy.OSF.ORG>
Date: 22 May 91 14:48:29 GMT
References: <1991May20.212338.24349@thyme.jpl.nasa.gov> <16211@smoke.brl.mil> <22051@paperboy.OSF.ORG> <16220@smoke.brl.mil>
Sender: news@OSF.ORG
Organization: Open Software Foundation
Lines: 25

In article <16220@smoke.brl.mil>, gwyn@smoke.brl.mil (Doug Gwyn) writes:
|> In article <22051@paperboy.OSF.ORG> dbrooks@osf.org (David Brooks) writes:
|> >The method you posted:
|> >	struct a_struct foo;
|> >	int offset2 = (char *)&foo.member2 - (char *)&foo; /* for example */
|> >has an unfortunate drawback.  You need to be able to declare foo, and
|> >squander space for it.  The ubiquitous uses in X don't have those luxuries.
|> 
|> No, you don't.  If you understood my example, you should be able to apply
|> the technique whenever you can latch onto, for example, a pointer to a
|> struct of the appropriate type.

As I said, the ubiquitous uses in X don't have that luxury.

|> The X11 source code style is ATROCIOUS and should not be used as a model.

Oh, I agree with that.  Looking at the macro, I'm always astounded that it
works.

However, the fact is, in two years of supporting folks using X, I've never
come across a pre-ANSI compiler that failed to handle the X macro.  And,
for ANSI compilers, with an official offsetof, it's moot.
-- 
David Brooks				dbrooks@osf.org
Systems Engineering, OSF		uunet!osf.org!dbrooks