Path: utzoo!attcan!uunet!mcsun!ukc!warwick!cudcv
From: cudcv@warwick.ac.uk (Rob McMahon)
Newsgroups: comp.lang.c
Subject: Re: Order of evalution of expressions.
Message-ID: <1990Sep19.105934.4218@warwick.ac.uk>
Date: 19 Sep 90 10:59:34 GMT
References: <6398@castle.ed.ac.uk>
Sender: news@warwick.ac.uk (Network news)
Organization: Computing Services, Warwick University, UK
Lines: 28

In article <6398@castle.ed.ac.uk> elee24@castle.ed.ac.uk (H Bruce) writes:
>Is the line
>
>value = *ptr - *ptr++;
>
>sensible C ?
>In other words is there a specified order of evaluation of expressions ?

Absolutely not, no.

>Would the following lines be optimized by a compiler (so that value is
>not loaded twice) ?
>
>value = *ptr;
>value -= *ptr++;

Well, gcc optimizes this to

	ptr++;
	value = 0;

I suspect your code may be wrong :-)

Rob
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Rob McMahon, Computing Services, Warwick University, Coventry CV4 7AL, England