Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!ptsfa!ames!elroy!cit-vax!oberon!skat.usc.edu!blarson
From: blarson@skat.usc.edu (Bob Larson)
Newsgroups: comp.lang.c
Subject: Re: comma operator
Message-ID: <6390@oberon.USC.EDU>
Date: 22 Jan 88 06:09:13 GMT
References: <3819@sigi.Colorado.EDU> <8599@ism780c.UUCP> <1866@bsu-cs.UUCP> <4006@june.cs.washington.edu> <3586@sdcc6.ucsd.EDU> <4018@june.cs.washington.edu> <2427@bloom-beacon.MIT.EDU> <4037@june.cs.washington.edu>
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In article <4037@june.cs.washington.edu> pardo@uw-june.UUCP (David Keppel) writes:
>    int	*ctrl_p = DISK_CTRL_REGISTER;
>    int	*out_p = DISK_OUT_REGISTER;
>
>    *ctrl_p = SETUP, *out_p = GO;
>
>which _relies_ on the evaluation order being guaranteed in a
>stronger way than is provided by sequence points.

Ansi C (all recent drafts, not yet a standard) adds the keyword
"volitile" for exactly this reason.  Change the declarations to

int *volitile ctrl_p;
int *volitile out_p;

and an ANSI compiler will not be allowed to rearange.

(I got this out of this group, I hope I have the volitile in the right
place.)
--
Bob Larson	Arpa: Blarson@Ecla.Usc.Edu	blarson@skat.usc.edu
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