Sender:	crough45 AT amc DOT de
Message-Id:	<97Aug8.112626gmt+0100.17059@internet01.amc.de>
Date:	Fri, 8 Aug 1997 10:29:01 +0100
From:	Chris Croughton <crough45 AT amc DOT de>
Mime-Version:	1.0
To:	charles AT pentek DOT com
Cc:	djgpp AT delorie DOT com
Subject:	Re: [Q] expression evaluation order

Charles Krug wrote:

> I think that ANSI tries to demand left-to-right evalutaion 
> of &&.  But not all compilers do this correctly.  To 
> guarantee left-to-right evaluation, you need:

Wrong.  ANSI states that && and || WILL be evaluated left
to right, and that the right hand side will not be executed
if the left is satisfied (false for &&, true for ||).

This is mandated behaviour, any compiler which does not do
this is not ANSI compliant, and a manufacturer attempting
to sell such a compiler as being ANSI compliant could be
sued.  Among other things, it will break a lof of the GNU
software including gcc itself.

One of the most common uses of this is in testing array 
elements, as in:

  if (i >= 0 && i < 10 && a[i] != x)
    ...

to prevent accessing invalid array elements.  This sort of
'defensive' code relies on the compiler working properly.

Chris C

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