Path: utzoo!utgpu!water!watmath!clyde!ima!think!barmar
From: barmar@think.COM (Barry Margolin)
Newsgroups: comp.lang.c
Subject: Re: volatile
Message-ID: <18642@think.UUCP>
Date: 30 Mar 88 02:38:40 GMT
References: <12578@brl-adm.ARPA> <1988Mar25.172355.348@utzoo.uucp> <588@imagine.PAWL.RPI.EDU> <1988Mar29.004454.2867@utzoo.uucp> <134@wyse.wyse.com>
Sender: usenet@think.UUCP
Reply-To: barmar@fafnir.think.com.UUCP (Barry Margolin)
Organization: Thinking Machines Corporation, Cambridge, MA
Lines: 27

In article <134@wyse.wyse.com> mikew@wyse.UUCP (Mike Wexler) writes:
>I would disagree that is isn't possible to write portable code that requires
>volatiles. An example(possibly the only one), is the use of System V
>or Berkeley shared memory.  With either of these you can have volatile
>values in portable(At least to similar Unix systems) programs.  Given
>this it might be useful for the Posix standard to require the C compiler
>to support volatile or a volatile pragma.

But such programs are NOT portable.  A program using System V shared
memory is not portable to a BSD system and vice-versa.  And none of
them are portable to non-Unix systems.

As you yourself implied in your last sentence, the right place for
such a requirement is in the Posix standard, not the C standard.  And
the mechanism that can be used for this is #pragma.  The C standard
doesn't specify the format of particular pragmas (whether this is wise
is debatable), but Posix already requires various extra C features
(for example, I believe it adds things to include files that are
specified in the C standard), so it could also require that compilers
implement a particular set of pragmas with a given syntax.


Barry Margolin
Thinking Machines Corp.

barmar@think.com
uunet!think!barmar