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From: edw@ius2.cs.cmu.edu.UUCP
Newsgroups: comp.lang.c
Subject: Re: Stupid evaluation ordering.  Is this legal?
Message-ID: <1104@ius2.cs.cmu.edu>
Date: Sat, 18-Apr-87 16:57:16 EST
Article-I.D.: ius2.1104
Posted: Sat Apr 18 16:57:16 1987
Date-Received: Sun, 19-Apr-87 08:20:51 EST
References: <4395@hi.uucp>
Organization: Carnegie-Mellon University, CS/RI
Lines: 36
Keywords: K&R, Bible, PCs, UNIX

In article <4395@hi.uucp>, josh@hi.uucp (Josh Siegel ) writes:
> I just lost a argument and am running to the net for comfort...
> 
> According to K&R(Bible) page 185,  a C compiler is allowed to do the
>  following.  
> 
> Given:
> 
> 	a(b()+c(),d()+e())
> 
> 	It is allowed to run functions b() and d(), then run
> 	c() and e(), THEN add them (This has shades of
> 	compilers that optimise on parallel machines).  
> 	This causes problems with stuff like:


   Never assume anything about the order of evaluation of parameters to
a function.  One thing, you are not guarenteed that b()+c() will be
evaluated before d()+e().  I know, I had code break because of this
very same thing.  I'm not sure,but you may not even be guarenteed that 
b() will be evaluated before c().  Is it consider a legal optimization -
to reorder the sequence of function calls within an expression?

-- 
					Eddie Wyatt

They say there are strangers, who threaten us
In our immigrants and infidels
They say there is strangeness, too dangerous
In our theatres and bookstore shelves
Those who know what's best for us-
Must rise and save us from ourselves

Quick to judge ... Quick to anger ... Slow to understand...
Ignorance and prejudice and fear [all] Walk hand in hand.
					- RUSH