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Groups > comp.lang.c > #55923

Re: the language

From James Kuyper <jameskuyper@verizon.net>
Newsgroups comp.lang.c
Subject Re: the language
Date 2015-01-05 13:19 -0500
Organization Self
Message-ID <54AAD5B2.9090409@verizon.net> (permalink)
References (17 earlier) <Vmeqw.180819$5r4.102802@fx31.iad> <m8btua$d8v$1@dont-email.me> <hffqw.1189226$Y4.451905@fx24.iad> <m8e85l$9f3$1@dont-email.me> <uTxqw.1059179$Fo3.656156@fx09.iad>

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On 01/05/2015 10:14 AM, Greg Martin wrote:
> On 2015-01-05, James Kuyper <jameskuyper@verizon.net> wrote:
>> On 01/04/2015 01:02 PM, Greg Martin wrote:
>>
>>> a++ = ++a - f(a--);
>>>
>>> where the compiler has no idea what I mean but will do it anyway?
>>
>> The behavior of that construct is undefined, but it could have been
>> implementation-defined. If it were, what you meant would be irrelevant -
>> the only thing that would be relevant is what the
>> implementation-provided definition of the behavior is. If that
>> definition meets your needs, use it. If not, rewrite your code to
>> explicitly evaluate the expressions with side effects in the order that
>> you desire.
> 
> If a compiler allows a construct, and converts it into machine code, 
> it "becomes" implementation defined anyways.

No - in the C context, "implementation-defined" is a term with a meaning
defined by the C standard - treating the term as if it were simply made
up of two words interpreted according to the rules of ordinary English
doesn't work. The relevant definition is:

"unspecified behavior where each implementation documents how the choice
is made". (3.4.1)

That definition, in turn, depends upon the definition of "unspecified
behavior":
"use of an unspecified value, or other behavior where this International
Standard provides two or more possibilities and imposes no further
requirements on which is chosen in any instance" (3.4.4)

The behavior of a construct in a C program is implementation-defined
only if the standard says so explicitly, and if it does, an
implementation can only conform to the standard if it actually documents
the behavior. Generating machine instructions that have a particular
behavior doesn't qualify as documenting the behavior. The documentation
has to specify what the behavior is in general, not just what it is when
compiling a particular program.

> ... I guess the difference is, 
> calling it undefined behavior suggests that the compiler doesn't need 
> to accept it but it may, ...

Not quite. Undefined behavior means that the standard imposes no
requirements on the behavior. Not requiring that it be accepted is only
one small part of the implications.
A conforming hosted implementation is required to accept any strictly
conforming programs. There's lots of things that can render a program
not strictly conforming; having undefined behavior is just one of those
things.

> calling it implementation defined means, there 
> isn't a standardized meaning for this but the implementation is 
> required to do something with it. 

No, it means the implementation is required to document it.

> It seems to me this largely only affects whether a compiler can be 
> said to be compliant or not but perhaps that's the point. 

Well, yes - ultimately, everything the C standard says boils down to
specifying what you need to know to determine
a) whether a given implementation is conforming
b) how well a given program conforms (there's a whole bunch of different
terms that could apply: conforming, strictly conforming, unspecified
behavior, implementation-defined behavior, undefined behavior, exceeds
minimum implmentation limits).

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the language Rosario193 <Rosario@invalid.invalid> - 2014-11-26 21:54 +0100
  Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-26 21:56 +0100
    Re: the language John Bode <jfbode1029@gmail.com> - 2014-11-26 13:45 -0800
      Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 11:52 +0100
      Re: the language "Bill Cunningham" <nospam@nspam.invalid> - 2014-12-01 23:25 -0500
      Re: the language "Bill Cunningham" <nospam@nspam.invalid> - 2014-12-02 00:56 -0500
        Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-04 14:52 +0100
          Re: the language "Osmium" <r124c4u102@comcast.net> - 2014-12-04 08:07 -0600
            Re: the language Geoff <geoff@invalid.invalid> - 2014-12-04 10:20 -0800
  Re: the language Mark Storkamp <mstorkamp@yahoo.com> - 2014-11-26 15:11 -0600
    Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 12:16 +0100
      Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 12:18 +0100
  Re: the language John Bode <jfbode1029@gmail.com> - 2014-11-26 13:12 -0800
    Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-11-27 00:37 +0000
    Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-11-27 01:13 +0000
  Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-11-26 22:45 +0000
    Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-27 07:41 +0100
  Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-27 08:12 +0100
    Re: the language Morris Dovey <mrdovey@iedu.com> - 2014-11-27 01:43 -0600
      Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 11:56 +0100
        Re: the language Morris Dovey <mrdovey@iedu.com> - 2014-11-28 09:08 -0600
          Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 20:58 +0100
            Re: the language Morris Dovey <mrdovey@iedu.com> - 2014-11-28 19:22 -0600
              Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-02 02:59 +0100
                Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-12-02 02:53 +0000
                Re: the language Les Cargill <lcargill99@comcast.com> - 2014-12-01 21:25 -0600
                Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-12-02 06:22 +0000
  Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-11-27 08:37 +0000
    Re: the language Reinhardt Behm <rbehm@hushmail.com> - 2014-11-27 16:44 +0800
      Re: the language gazelle@shell.xmission.com (Kenny McCormack) - 2014-11-27 15:35 +0000
        Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-11-27 11:58 -0500
          Re: the language jt@toerring.de (Jens Thoms Toerring) - 2014-11-27 22:44 +0000
            Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 09:52 +0100
            Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-11-28 12:53 -0800
          Re: the language Thomas Jahns <jahns@idontlikespam.dkrz.de> - 2014-11-28 10:07 +0100
            Re: the language Thomas Jahns <jahns@idontlikespam.dkrz.de> - 2014-11-28 14:57 +0100
            Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-11-28 13:09 -0800
    Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 12:01 +0100
      Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-11-28 14:46 +0000
    Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-11-28 13:16 -0800
      Re: the language gazelle@shell.xmission.com (Kenny McCormack) - 2014-11-28 22:09 +0000
        Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-01 03:40 -0800
      Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 14:42 -0800
        Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-01 03:22 -0800
      Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-11-28 23:09 +0000
        Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 16:14 -0800
          Re: the language BartC <bc@freeuk.com> - 2014-11-29 01:42 +0000
          Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-11-29 01:42 +0000
            Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-29 04:03 -0800
          Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-01 00:55 -0800
            Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-02 05:42 +0000
        Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-11-28 19:25 -0500
        Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-01 03:21 -0800
          Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-01 14:02 +0000
            Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-05 10:18 -0800
              Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-07 08:25 +0000
                Re: the language Öö Tiib <ootiib@hot.ee> - 2014-12-07 10:44 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-07 19:17 +0000
                Re: the language Öö Tiib <ootiib@hot.ee> - 2014-12-07 15:48 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-08 05:45 +0000
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-08 03:27 -0800
                Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-12-08 06:00 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-08 06:17 +0000
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-08 03:37 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-08 12:53 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-16 04:21 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-16 12:43 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-16 14:46 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-17 00:23 +0000
                Re: the language JohnF <john@please.see.sig.for.email.com> - 2014-12-17 07:01 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-17 07:22 +0000
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-17 11:56 +0000
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-17 05:43 -0800
                Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-18 18:30 +0100
                Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-18 18:41 +0100
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-17 14:34 +0000
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-18 02:15 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-17 22:31 -0500
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-18 17:19 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-18 07:52 +0000
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-18 17:21 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-18 18:15 +0000
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-19 01:20 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 07:48 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 07:40 -0500
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 12:54 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 09:54 -0500
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 15:19 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 11:00 -0500
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 16:13 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 11:27 -0500
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 16:45 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 13:48 -0500
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 19:10 +0000
                Re: the language Morris Dovey <mrdovey@iedu.com> - 2014-12-19 21:17 -0600
                Re: the language Morris Dovey <mrdovey@iedu.com> - 2014-12-19 21:32 -0600
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-19 16:49 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 17:00 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-19 13:57 -0500
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-19 14:31 -0800
                Re: the language Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-12-19 20:29 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 20:36 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-17 07:18 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-17 15:45 +0000
                Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-17 16:50 +0000
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-17 17:24 +0000
                Re: the language Robert Wessel <robertwessel2@yahoo.com> - 2014-12-18 02:07 -0600
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-18 12:04 +0000
                Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-12-18 08:06 -0500
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-18 08:30 -0500
                Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-12-19 00:11 -0500
                Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-19 07:00 +0000
                Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-19 08:43 -0800
                Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-12-19 23:29 -0500
                Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-20 00:37 -0800
                Re: the language gazelle@shell.xmission.com (Kenny McCormack) - 2014-12-20 08:45 +0000
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-20 09:45 +0000
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-20 03:17 -0800
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-18 06:09 -0800
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-18 14:30 +0000
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-18 14:23 +0000
                Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-18 08:18 -0800
                Re: the language Richard Damon <Richard@Damon-Family.org> - 2014-12-20 12:22 -0500
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2014-12-20 13:36 -0500
                Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-20 11:43 -0800
                Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-20 11:37 -0800
                Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-20 20:10 +0000
                Re: the language Robert Wessel <robertwessel2@yahoo.com> - 2014-12-21 15:02 -0600
                Re: the language Kaz Kylheku <kaz@kylheku.com> - 2014-12-21 22:02 +0000
                Re: the language Stephen Sprunk <stephen@sprunk.org> - 2014-12-21 23:49 -0600
                Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-21 17:45 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-18 10:29 -0800
                Re: the language Robert Wessel <robertwessel2@yahoo.com> - 2014-12-20 05:29 -0600
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-20 11:32 -0800
                Re: the language Robert Wessel <robertwessel2@yahoo.com> - 2014-12-21 15:23 -0600
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-22 23:39 -0800
                Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-12-20 20:22 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-18 10:24 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-18 18:36 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-19 09:24 -0800
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 17:53 +0000
                Re: the language Tim Rentsch <txr@alumni.caltech.edu> - 2014-12-20 11:48 -0800
                Re: the language JohnF <john@please.see.sig.for.email.com> - 2014-12-19 02:20 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 08:31 +0000
                Re: the language JohnF <john@please.see.sig.for.email.com> - 2014-12-19 09:31 +0000
                Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-19 10:10 +0000
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-19 07:08 -0800
                Re: the language JohnF <john@please.see.sig.for.email.com> - 2014-12-20 06:39 +0000
                Re: the language John Forkosh <forkosh@panix.com> - 2014-12-20 07:32 +0000
                Re: the language Greg Martin <greg.at.softsprocket@dot.com> - 2015-01-04 17:02 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2015-01-04 12:40 -0500
                Re: the language Greg Martin <greg.at.softsprocket@dot.com> - 2015-01-04 18:02 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2015-01-05 09:47 -0500
                Re: the language Greg Martin <greg.at.softsprocket@dot.com> - 2015-01-05 15:14 +0000
                Re: the language Keith Thompson <kst-u@mib.org> - 2015-01-05 08:42 -0800
                Re: the language glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-01-06 00:14 +0000
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2015-01-05 13:19 -0500
                Re: the language Richard Damon <Richard@Damon-Family.org> - 2015-01-04 15:59 -0500
                Re: the language Keith Thompson <kst-u@mib.org> - 2015-01-04 14:30 -0800
                Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-01-04 15:44 -0800
                Re: the language James Kuyper <jameskuyper@verizon.net> - 2015-01-05 13:36 -0500
  Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-11-28 12:07 +0100
  Re: the language "ocq (an evil corporate man)" <ocq@maili.ng> - 2014-12-02 23:16 +0100
    Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-03 02:23 -0800
      Re: the language "ocq (an evil corporate man)" <ocq@maili.ng> - 2014-12-03 15:55 +0100
      Re: the language Nobody <nobody@nowhere.invalid> - 2014-12-03 15:42 +0000
        Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-04 04:49 -0800
          Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-04 09:07 -0800
            Re: the language Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-12-04 10:08 -0800
              Re: the language Keith Thompson <kst-u@mib.org> - 2014-12-04 11:49 -0800
                Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-05 12:32 +0100
          Re: the language raltbos@xs4all.nl (Richard Bos) - 2014-12-04 22:17 +0000
  Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-18 18:17 +0100
    Re: the language Richard Heathfield <invalid@see.sig.invalid> - 2014-12-18 18:12 +0000
      Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-18 23:15 +0100
        Re: the language Rosario193 <Rosario@invalid.invalid> - 2014-12-18 23:50 +0100
    Re: the language "ocq (an evil corporate man)" <ocq@maili.ng> - 2014-12-19 02:34 +0100

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