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From: kaz@vision.crest.nt.com (Kaz Kylheku)
Subject: Re: Not intended for use in medical,
Date: 1997/05/06
Message-ID: <5kmek2$9re@bcrkh13.bnr.ca>#1/1
X-Deja-AN: 239667514
References: <3.0.32.19970423164855.00746db8@mail.4dcomm.com>
 <5kgu95$kb7@bcrkh13.bnr.ca> <dewar.862775250@merv>
 <5kl9qc$g4d@bcrkh13.bnr.ca>
Organization: Prism Systems Inc.
Newsgroups: comp.lang.ada
Date: 1997-05-06T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <5kl9qc$g4d@bcrkh13.bnr.ca>,
Kaz Kylheku <kaz@vision.crest.nt.com> wrote:
>In article <dewar.862775250@merv>, Robert Dewar <dewar@merv.cs.nyu.edu> wrote:
>>Kaz said
>>
>><<Sorry about this C intrusion into comp.lang.ada. I didn't intend that
>>  example to spark a discussion about C semantics, but just to clear up,
>>  the && operator in C has sequencing properties. Its left constituent
>>  must not only be evaluated before its right, but its side effects must
>>  also be settled before the left side is evaluated. Hence   x++ && x++  is
>>  perfectly well defined. The program I was writing depended on this crucial
>>  sequencing property.>>
>>
>>  Yes, legal, but horrible. A good reminder of why Ada does NOT have
>>  the ++ operator built in :-)

By the way, the x++ is just another way of writing the assignment expression x
+= 1, or x = x + 1 (the latter case evaluates x twice, of course).  The real
``evil'' perhaps is that in C an assignment is an expression rather than a
statement, so that you can decorate a complex expression with assignments all
over the place.

Note that this is one of the areas of C which C++ _worsens_ significantly.
In C++, the result of an assignment expression is not only an expression
itself, but it is also an _lvalue_. Talk about lunacy.

With one stroke, the C++ ``designers'' introduce a whole new batch of nonsense,
such as 

    (i = x) = y;

which must be rejected by any conforming C implementation as constraint
violation. 

What's the final value of i? Is it x? Or is it y?
My friend, do not waste your time: the behavior's undefined.

Better C indeed! :)