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From: kaz@vision.crest.nt.com (Kaz Kylheku)
Subject: Re: Not intended for use in medical,
Date: 1997/05/06
Date: 1997-05-06T00:00:00+00:00	[thread overview]
Message-ID: <5kmek2$9re@bcrkh13.bnr.ca> (raw)
In-Reply-To: 5kl9qc$g4d@bcrkh13.bnr.ca


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! :)




  reply	other threads:[~1997-05-06  0:00 UTC|newest]

Thread overview: 127+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
1997-04-23  0:00 Not intended for use in medical, Robert C. Leif, Ph.D.
1997-04-24  0:00 ` J. Florio
1997-04-25  0:00 ` Ken Garlington
1997-04-25  0:00 ` Kevin Cline
1997-04-25  0:00   ` Robert Dewar
1997-04-28  0:00 ` John Apa
1997-04-28  0:00   ` Robert Dewar
1997-04-29  0:00     ` Kaz Kylheku
1997-04-30  0:00       ` John Apa
     [not found]       ` <3367CE1E.5ED1@die_spammer.dasd.honeywell.com>
1997-05-01  0:00         ` Kaz Kylheku
1997-05-03  0:00       ` Simon Wright
1997-05-04  0:00         ` Kaz Kylheku
1997-05-04  0:00           ` Robert Dewar
1997-05-04  0:00             ` Richard Kenner
1997-05-05  0:00             ` Kaz Kylheku
1997-05-06  0:00               ` Kaz Kylheku [this message]
1997-05-06  0:00                 ` Robert A Duff
1997-05-07  0:00                   ` Kaz Kylheku
1997-05-08  0:00                     ` Robert A Duff
1997-05-07  0:00                   ` Robert Dewar
1997-05-08  0:00                     ` John G. Volan
1997-05-10  0:00                       ` Robert Dewar
1997-05-10  0:00                         ` John G. Volan
1997-05-11  0:00                           ` Robert Dewar
1997-05-11  0:00                             ` John G. Volan
1997-05-11  0:00                               ` Robert A Duff
1997-05-12  0:00                                 ` John G. Volan
1997-05-12  0:00                                 ` Robert Dewar
1997-05-11  0:00                             ` John G. Volan
1997-05-11  0:00                               ` Robert Dewar
1997-05-12  0:00                             ` John G. Volan
1997-05-12  0:00                               ` Robert Dewar
1997-05-17  0:00                               ` Robert I. Eachus
     [not found]                                 ` <dewar.863877808@merv>
1997-05-17  0:00                                   ` Robert Dewar
1997-05-17  0:00                                     ` Jon S Anthony
1997-05-21  0:00                                       ` Syntax for tagged record types (was Re: Not intended for use in medical,) Ben Brosgol
1997-05-20  0:00                                         ` Matthew Heaney
1997-05-21  0:00                                           ` Syntax for tagged record types and class types Mats Weber
1997-05-21  0:00                                             ` Matthew Heaney
1997-05-22  0:00                                               ` Mats Weber
1997-05-27  0:00                                               ` Tucker Taft
1997-05-30  0:00                                                 ` Mats.Weber
1997-05-22  0:00                                             ` Samuel A. Mize
1997-05-22  0:00                                               ` Samuel A. Mize
1997-05-23  0:00                                               ` Mats Weber
1997-05-21  0:00                                           ` Syntax for tagged record types (was Re: Not intended for use in medical,) Jon S Anthony
1997-05-21  0:00                                             ` Matthew Heaney
1997-05-22  0:00                                               ` Robert I. Eachus
1997-05-25  0:00                                                 ` Matthew Heaney
1997-05-28  0:00                                                   ` Robert I. Eachus
1997-05-23  0:00                                               ` Jon S Anthony
1997-05-23  0:00                                                 ` Simon Wright
1997-05-23  0:00                                                 ` Matthew Heaney
1997-05-25  0:00                                                   ` Jon S Anthony
1997-05-28  0:00                                                   ` Syntax for tagged record types (was Re David Kristola
     [not found]                                         ` <mheaney-ya023680002005972314260001@news.ni.net <mheaney-ya023680002105972302430001@news.ni.net>
1997-05-22  0:00                                           ` Syntax for tagged record types (was Re: Not intended for use in medical,) Robert A Duff
1997-05-22  0:00                                             ` John G. Volan
1997-05-23  0:00                                               ` Matthew Heaney
1997-05-23  0:00                                                 ` Jon S Anthony
1997-05-23  0:00                                                   ` Matthew Heaney
1997-05-25  0:00                                                     ` Robert Dewar
1997-05-25  0:00                                                     ` Jon S Anthony
1997-05-27  0:00                                                     ` Ray Blaak
1997-05-23  0:00                                                   ` John G. Volan
1997-05-24  0:00                                                     ` Robert A Duff
1997-05-24  0:00                                                       ` Matthew Heaney
1997-05-28  0:00                                                         ` Robert I. Eachus
1997-05-25  0:00                                                     ` Jon S Anthony
1997-05-23  0:00                                               ` Jon S Anthony
1997-05-12  0:00                             ` Not intended for use in medical, John G. Volan
1997-05-12  0:00                         ` Language Design Mistakes (was "not intended...") W. Wesley Groleau (Wes)
1997-05-13  0:00                           ` Robert Dewar
1997-05-13  0:00                             ` W. Wesley Groleau (Wes)
1997-05-13  0:00                             ` Robert A Duff
1997-05-14  0:00                               ` Robert Dewar
1997-05-08  0:00                     ` Not intended for use in medical, Robert A Duff
1997-05-09  0:00                       ` Robert I. Eachus
1997-05-11  0:00                         ` Robert Dewar
1997-05-11  0:00                           ` Matthew Heaney
1997-05-12  0:00                             ` Robert Dewar
1997-05-12  0:00                               ` Matthew Heaney
1997-05-13  0:00                                 ` Jon S Anthony
1997-05-13  0:00                                   ` Matthew Heaney
1997-05-14  0:00                                     ` Robert Dewar
1997-05-14  0:00                                     ` Robert Dewar
1997-05-14  0:00                                 ` Robert Dewar
1997-05-14  0:00                                 ` Nick Roberts
1997-05-14  0:00                                 ` Robert Dewar
1997-05-15  0:00                                   ` W. Wesley Groleau (Wes)
1997-05-12  0:00                           ` Robert I. Eachus
1997-05-13  0:00                             ` Robert Dewar
1997-05-14  0:00                               ` Nick Roberts
1997-05-14  0:00                                 ` Robert Dewar
     [not found]                                   ` <01bc6182$30e3a7c0$LocalHost@xhv46.dial.pipex.com>
1997-05-16  0:00                                     ` Robert Dewar
1997-05-16  0:00                                     ` Robert A Duff
1997-05-16  0:00                                       ` Robert I. Eachus
1997-05-18  0:00                                         ` Nick Roberts
1997-05-18  0:00                                           ` Matthew Heaney
1997-05-19  0:00                                             ` Robert I. Eachus
1997-05-19  0:00                                               ` Matthew Heaney
1997-05-20  0:00                                                 ` Nick Roberts
1997-05-20  0:00                                                   ` Matthew Heaney
1997-05-21  0:00                                                     ` Dale Stanbrough
1997-05-19  0:00                                             ` Robert A Duff
1997-05-08  0:00                     ` Kaz Kylheku
1997-05-08  0:00                       ` Robert Dewar
1997-05-09  0:00                         ` Kaz Kylheku
1997-05-12  0:00                       ` W. Wesley Groleau (Wes)
1997-05-12  0:00                         ` John G. Volan
1997-05-14  0:00                       ` Nick Roberts
1997-05-14  0:00                         ` Robert Dewar
1997-05-14  0:00                           ` Jeff Carter
     [not found]                             ` <dewar.863632434@merv>
1997-05-15  0:00                               ` Kaz Kylheku
1997-05-18  0:00                                 ` Robert Dewar
1997-05-15  0:00                         ` Kaz Kylheku
1997-05-04  0:00         ` Richard Kenner
1997-05-04  0:00         ` Robert Dewar
1997-04-28  0:00   ` John M. Mills
1997-04-30  0:00     ` Larry Kilgallen
1997-05-02  0:00       ` Nick Roberts
  -- strict thread matches above, loose matches on Subject: below --
1997-04-25  0:00 Robert C. Leif, Ph.D.
1997-05-12  0:00 Marin David Condic, 561.796.8997, M/S 731-93
1997-05-13  0:00 ` Robert Dewar
1997-05-14  0:00 tmoran
1997-05-14  0:00 Marin David Condic, 561.796.8997, M/S 731-93
1997-05-14  0:00 Marin David Condic, 561.796.8997, M/S 731-93
1997-05-19  0:00 Robert C. Leif, Ph.D.
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