Re: Is goto Still Considered Harmful?

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.fortran, comp.lang.c
Subject	Re: Is goto Still Considered Harmful?
Date	2014-03-13 16:46 -0700
Organization	None to speak of
Message-ID	<lny50dpsqf.fsf@nuthaus.mib.org> (permalink)
References	(1 earlier) <GOTO-20140312232357@ram.dialup.fu-berlin.de> <lft6qa$svi$1@newsreader4.netcologne.de> <debugging-20140313232851@ram.dialup.fu-berlin.de> <20140313153944.695@kylheku.com> <lfte37$p8k$1@dont-email.me>

Cross-posted to 2 groups.

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"James Van Buskirk" <not_valid@comcast.net> writes:
> "Kaz Kylheku" <kaz@kylheku.com> wrote in message 
> news:20140313153944.695@kylheku.com...
>
>> Why bring up Java; we have that in C:
>
>>  assert (var = true); /* doesn't happen if NDEBUG is on */
>
> At last!  A C programmer to inflict the Question on!  Now, what if
> true is a const _Bool with internal representation B'00000010'
> and var is also an _Bool.  Does the assert happen if NDEBUG is not
> on?

Since `var = true` is an assignment, yes, the assert will fire.

Let's assume that the `= true` is replaced by `== true` (though it would
be better to omit it altogether and write `assert(var);`).

If there's a visible `#include <stdbool.h>` directive, then `true` is a
macro that expands to 1, so to satisfy your assumptions we have to
assume that the programmer has (foolishly) redefined `true` -- but how?

Converting any scalar value to _Bool yields 0 if the value is equal to
0, 1 if it's not, which makes it difficult to construct a _Bool value
other than 0 or 1.

If you manage do so, it's likely that your program's behavior has become
undefined while doing so, which means the assert happen, or it may not
happen, or the walls might start to bleed.

The simple answer is: Don't do that.

But if you want an answer beyond that, I suggest you show the specific C
code you're asking about.

(Incidentally, B'00000010' is not C syntax, but it's obvious enough what
you mean.)

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thread

Is goto Still Considered Harmful? Lynn McGuire <lmc@winsim.com> - 2014-03-12 11:02 -0500
  Re: Is goto Still Considered Harmful? James Kuyper <jameskuyper@verizon.net> - 2014-03-12 12:17 -0400
  Re: Is goto Still Considered Harmful? nospam@see.signature (Richard Maine) - 2014-03-12 09:20 -0700
    Re: Is goto Still Considered Harmful? Lynn McGuire <lmc@winsim.com> - 2014-03-18 16:30 -0500
      Re: Is goto Still Considered Harmful? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-18 21:48 +0000
        Re: Is goto Still Considered Harmful? Lynn McGuire <lmc@winsim.com> - 2014-03-18 19:10 -0500
          Re: Is goto Still Considered Harmful? "Terence" <tbwright@bigpond.net.au> - 2014-03-19 20:39 +1100
          Re: Is goto Still Considered Harmful? ftinetti@gmail.com - 2014-03-19 03:41 -0700
      Re: Is goto Still Considered Harmful? ftinetti@gmail.com - 2014-03-18 16:45 -0700
      Re: Is goto Still Considered Harmful? dpb <none@non.net> - 2014-03-18 19:14 -0500
      Re: Is goto Still Considered Harmful? Geoff <geoff@invalid.invalid> - 2014-03-18 17:36 -0700
        Re: Is goto Still Considered Harmful? James Kuyper <jameskuyper@verizon.net> - 2014-03-19 07:34 -0400
          Re: Is goto Still Considered Harmful? "BartC" <bc@freeuk.com> - 2014-03-19 12:08 +0000
            Re: Is goto Still Considered Harmful? James Kuyper <jameskuyper@verizon.net> - 2014-03-19 10:07 -0400
              Re: Is goto Still Considered Harmful? Richard <rgrdev_@gmail.com> - 2014-03-19 17:05 +0100
            Re: Is goto Still Considered Harmful? Lynn McGuire <lmc@winsim.com> - 2014-03-19 12:27 -0500
              Re: Is goto Still Considered Harmful? dpb <none@non.net> - 2014-03-19 13:04 -0500
                Re: Is goto Still Considered Harmful? dpb <none@non.net> - 2014-03-19 13:26 -0500
                Re: Is goto Still Considered Harmful? Lynn McGuire <lmc@winsim.com> - 2014-03-19 13:36 -0500
                Re: Is goto Still Considered Harmful? dpb <none@non.net> - 2014-03-19 14:02 -0500
                Re: Is goto Still Considered Harmful? Lynn McGuire <lmc@winsim.com> - 2014-03-19 13:36 -0500
              Re: Is goto Still Considered Harmful? Gordon Sande <Gordon.Sande@gmail.com> - 2014-03-19 16:48 -0300
      Re: Is goto Still Considered Harmful? "Terence" <tbwright@bigpond.net.au> - 2014-03-19 20:35 +1100
        Re: Is goto Still Considered Harmful? Lynn McGuire <lmc@winsim.com> - 2014-03-19 12:26 -0500
  Re: Is goto Still Considered Harmful? Gordon Sande <Gordon.Sande@gmail.com> - 2014-03-12 13:23 -0300
    Re: Is goto Still Considered Harmful? e p chandler <epc8@juno.com> - 2014-03-12 10:05 -0700
  Re: Is goto Still Considered Harmful? Kaz Kylheku <kaz@kylheku.com> - 2014-03-12 16:47 +0000
  Re: Is goto Still Considered Harmful? "BartC" <bc@freeuk.com> - 2014-03-12 18:50 +0000
    Re: Is goto Still Considered Harmful? Gordon Sande <Gordon.Sande@gmail.com> - 2014-03-12 16:16 -0300
    Re: Is goto Still Considered Harmful? <william@wilbur.25thandClement.com> - 2014-03-12 12:49 -0700
    Re: Is goto Still Considered Harmful? "Qolin" <noone@nowhere.com> - 2014-03-12 21:54 +0000
      Re: Is goto Still Considered Harmful? Lynn McGuire <lmc@winsim.com> - 2014-03-12 16:57 -0500
        Re: Is goto Still Considered Harmful? "Qolin" <noone@nowhere.com> - 2014-03-12 22:00 +0000
          Re: Is goto Still Considered Harmful? John Harper <john.harper@vuw.ac.nz> - 2014-03-13 11:23 +1300
      Re: Is goto Still Considered Harmful? Keith Thompson <kst-u@mib.org> - 2014-03-12 15:36 -0700
      Re: Is goto Still Considered Harmful? Robert Wessel <robertwessel2@yahoo.com> - 2014-03-12 23:40 -0500
        Re: Is goto Still Considered Harmful? David Brown <david.brown@hesbynett.no> - 2014-03-13 11:25 +0100
        Re: Is goto Still Considered Harmful? Thomas Jahns <jahns@idontlikespam.dkrz.de> - 2014-03-14 11:24 +0100
          Re: Is goto Still Considered Harmful? Robert Wessel <robertwessel2@yahoo.com> - 2014-03-14 23:32 -0500
          Re: Is goto Still Considered Harmful? Dr Nick <nospam-4@temporary-address.org.uk> - 2014-03-15 13:43 +0000
            Re: Is goto Still Considered Harmful? David Brown <david.brown@hesbynett.no> - 2014-03-15 16:28 +0100
              Re: Is goto Still Considered Harmful? Dr Nick <nospam-4@temporary-address.org.uk> - 2014-03-15 16:01 +0000
                Re: Is goto Still Considered Harmful? David Brown <david.brown@hesbynett.no> - 2014-03-17 08:51 +0100
    Re: Is goto Still Considered Harmful? David Brown <david.brown@hesbynett.no> - 2014-03-13 11:22 +0100
  Re: Is goto Still Considered Harmful? Jake <thatcadguy@gmail.com> - 2014-03-12 12:25 -0700
  Re: Is goto Still Considered Harmful? ralph <nt_consulting@yahoo.com> - 2014-03-12 15:34 -0500
  Re: Is goto Still Considered Harmful? jt@toerring.de (Jens Thoms Toerring) - 2014-03-13 01:06 +0000
    Re: Is goto Still Considered Harmful? fj <francois.jacq@irsn.fr> - 2014-03-12 18:31 -0700
      Re: Is goto Still Considered Harmful? wclodius@earthlink.net (William Clodius) - 2014-03-12 21:08 -0600
        Re: Is goto Still Considered Harmful? Dick Hendrickson <dick.hendrickson@att.net> - 2014-03-13 10:54 -0500
          Re: Is goto Still Considered Harmful? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-13 19:53 +0000
            Re: Is goto Still Considered Harmful? "Qolin" <noone@nowhere.com> - 2014-03-13 20:16 +0000
          Re: Is goto Still Considered Harmful? wclodius@earthlink.net (William Clodius) - 2014-03-13 21:57 -0600
    Re: Is goto Still Considered Harmful? wilson <winslole@udayton.edu> - 2014-03-13 03:59 -0400
      Re: Is goto Still Considered Harmful? wilson <winslole@udayton.edu> - 2014-03-13 05:02 -0400
    Re: Is goto Still Considered Harmful? Louis Krupp <lkrupp@nospam.pssw.com.invalid> - 2014-03-13 07:42 -0600
      Re: Is goto Still Considered Harmful? Richard <rgrdev_@gmail.com> - 2014-03-13 14:56 +0100
  Re: Is goto Still Considered Harmful? robin.vowels@gmail.com - 2014-03-13 00:59 -0700
  Re: Is goto Still Considered Harmful? Wolfgang Kilian <kilian@invalid.com> - 2014-03-13 09:10 +0100
  Re: Is goto Still Considered Harmful? Thomas Koenig <tkoenig@netcologne.de> - 2014-03-13 21:09 +0000
    Re: Is goto Still Considered Harmful? "Qolin" <noone@nowhere.com> - 2014-03-13 21:24 +0000
      Re: Is goto Still Considered Harmful? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-13 22:36 +0000
        Re: Is goto Still Considered Harmful? nospam@see.signature (Richard Maine) - 2014-03-13 17:54 -0700
          Re: Is goto Still Considered Harmful? robert.corbett@oracle.com - 2014-03-13 23:43 -0700
        Re: Is goto Still Considered Harmful? robin.vowels@gmail.com - 2014-03-13 18:07 -0700
        Re: Is goto Still Considered Harmful? Robert Wessel <robertwessel2@yahoo.com> - 2014-03-13 23:02 -0500
          Re: Is goto Still Considered Harmful? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-14 04:07 +0000
            Re: Is goto Still Considered Harmful? Robert Wessel <robertwessel2@yahoo.com> - 2014-03-13 23:56 -0500
          Re: Is goto Still Considered Harmful? helbig@astro.multiCLOTHESvax.de (Phillip Helbig---undress to reply) - 2014-03-14 09:17 +0000
        Re: Is goto Still Considered Harmful? Thomas Koenig <tkoenig@netcologne.de> - 2014-03-15 11:57 +0000
          Re: Is goto Still Considered Harmful? wclodius@earthlink.net (William Clodius) - 2014-03-15 16:38 -0600
            Re: Is goto Still Considered Harmful? Gary Scott <garylscott@sbcglobal.net> - 2014-03-15 18:09 -0500
              Re: Is goto Still Considered Harmful? wclodius@earthlink.net (William Clodius) - 2014-03-15 19:57 -0600
                Re: Is goto Still Considered Harmful? nospam@see.signature (Richard Maine) - 2014-03-15 19:41 -0700
    Re: Is goto Still Considered Harmful? Kaz Kylheku <kaz@kylheku.com> - 2014-03-13 22:42 +0000
      Re: Is goto Still Considered Harmful? "James Van Buskirk" <not_valid@comcast.net> - 2014-03-13 17:13 -0600
        Re: Is goto Still Considered Harmful? Keith Thompson <kst-u@mib.org> - 2014-03-13 16:46 -0700
          Re: Is goto Still Considered Harmful? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-14 01:17 +0000
            Re: Is goto Still Considered Harmful? Robert Wessel <robertwessel2@yahoo.com> - 2014-03-13 23:04 -0500
              Re: Is goto Still Considered Harmful? David Brown <david.brown@hesbynett.no> - 2014-03-14 10:41 +0100
                Re: Is goto Still Considered Harmful? Kaz Kylheku <kaz@kylheku.com> - 2014-03-14 09:55 +0000
                Re: Is goto Still Considered Harmful? David Brown <david.brown@hesbynett.no> - 2014-03-14 13:16 +0100
                Re: Is goto Still Considered Harmful? Seebs <usenet-nospam@seebs.net> - 2014-03-18 21:08 +0000
                Re: Is goto Still Considered Harmful? James Kuyper <jameskuyper@verizon.net> - 2014-03-18 17:41 -0400
            Re: Is goto Still Considered Harmful? robin.vowels@gmail.com - 2014-03-20 03:55 -0700
        Re: Is goto Still Considered Harmful? Kaz Kylheku <kaz@kylheku.com> - 2014-03-14 00:45 +0000
          Re: Is goto Still Considered Harmful? "James Van Buskirk" <not_valid@comcast.net> - 2014-03-13 21:40 -0600
            Re: Is goto Still Considered Harmful? James Kuyper <jameskuyper@verizon.net> - 2014-03-14 01:02 -0400
              Re: Is goto Still Considered Harmful? "James Van Buskirk" <not_valid@comcast.net> - 2014-03-14 10:36 -0600
                Re: Is goto Still Considered Harmful? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-14 17:30 +0000
                Re: Is goto Still Considered Harmful? James Kuyper <jameskuyper@verizon.net> - 2014-03-14 13:51 -0400
                Re: Is goto Still Considered Harmful? Keith Thompson <kst-u@mib.org> - 2014-03-14 13:12 -0700
            Re: Is goto Still Considered Harmful? Kaz Kylheku <kaz@kylheku.com> - 2014-03-14 05:29 +0000
              Re: Is goto Still Considered Harmful? "James Van Buskirk" <not_valid@comcast.net> - 2014-03-14 10:47 -0600
                Re: Is goto Still Considered Harmful? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-14 17:43 +0000
                Re: Is goto Still Considered Harmful? James Kuyper <jameskuyper@verizon.net> - 2014-03-14 13:52 -0400
            Re: Is goto Still Considered Harmful? Stephen Sprunk <stephen@sprunk.org> - 2014-03-16 17:15 -0500
              Re: Is goto Still Considered Harmful? Keith Thompson <kst-u@mib.org> - 2014-03-16 16:04 -0700
    Re: Is goto Still Considered Harmful? Kaz Kylheku <kaz@kylheku.com> - 2014-03-14 05:11 +0000
  Re: Is goto Still Considered Harmful? "Terence" <tbwright@bigpond.net.au> - 2014-03-14 08:32 +1100
    Re: Is goto Still Considered Harmful? Richard Damon <Richard@Damon-Family.org> - 2014-03-14 23:10 -0400

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