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Groups > comp.lang.c > #127057
| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Opinion sought: Is this strictly conforming C? |
| Date | 2018-02-25 15:36 -0800 |
| Organization | None to speak of |
| Message-ID | <ln4lm4k5g7.fsf@kst-u.example.com> (permalink) |
| References | (2 earlier) <5e795363-40ed-4405-9f4c-86ba404dad77@googlegroups.com> <kfnzi41trxl.fsf@x-alumni2.alumni.caltech.edu> <f50cd5f8-a0e9-4926-8b18-b683ba21bec8@googlegroups.com> <kfneflat717.fsf@x-alumni2.alumni.caltech.edu> <b58c0bac-85cd-459b-af95-6e477a638914@googlegroups.com> |
supercat@casperkitty.com writes:
[...]
> There are a number of situations where the behavior of some
> action would be described by the combination of the Standard
> and an implementation's documentation and yet also classified
> as Undefined. There are at least two ways one can interpret
> such an apparent contradiction:
>
> 1. Interpret the statement that the behavior is undefined as
> saying that the Standard imposes no requirements on the
> behavior of that action on any implementation, *even those
> where it would be defined elsewhere*.
That's what "undefined behavior" means:
behavior, upon use of a nonportable or erroneous program construct
or of erroneous data, for which this International Standard imposes
no requirements
For example, a secondary standard might define the behavior of
some construct whose behavior is not defined by the C standard.
An implementation that conforms to such a secondary standard is
required to behave accordingly -- but it's not required to do so
*by the C standard*.
This isn't complicated.
> 2. Interpret the statement that the behavior is undefined as
> saying that there is no requirement that implementations
> treat the behavior as defined *except when it is defined
> elsewhere*.
I'm not at all sure what this means. Implementations are already
required to obey any requirements imposed by secondary standards --
but such requirements are imposed by those secondary standards.
If you're suggesting that the C standard should require such
conformance, I don't see the point.
> The Standard makes no distinction between these two forms; applying
> the first consistently would yield a silly language in which many
> constructs would be all but useless [e.g. arrays of non-character
> types, or structures or unions that contain non-character members,
> could only have their elements or members accessed using memcpy
> other character-based means],
I think you've gotten stuck on the idea that N1570 6.5p7 implies that
this:
int arr[10];
arr[5] = 42;
has undefined behavior because it accesses arr (of type int[10]) using
an lvalue of type int.
It's obvious that the above is intended to be well defined by
the C standard. It's possible that there's a flaw in 6.5p7 that
seemingly makes it undefined (I haven't studied it closely enough
to have an opinion one way or the other). If there is such a flaw,
the solution is to fix the flaw, not to throw away the meaning of
"undefined behavior" and reinterpret the standard according to
your preferences.
> while applying the second
> consistently would yield a language which both useful and practical
> to implement.
>
> If the first interpretation should be used in some places, but
> the second should be used in others, different terminology should
> be used to distinguish them.
>
> You may regard the second interpretation as delusional, but the
> first would be absurd and I don't really see any basis for saying
> that the first interpretation is correct in places where it is too
> totally absurd, in which case the second should apply.
How about this?
1. Conforming C implementations are required to obey the requirements
of the C standard.
2. C implementations that claim to conform a secondary standard are
require to obey the requirements of the secondary standard. (This
requirement is, of course, imposed by the secondary standard, not by
the C standard.)
I think that is practically equivalent to your second interpretation --
and it reflects reality.
--
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"
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Opinion sought: Is this strictly conforming C? lee@ansync.com - 2018-02-15 17:20 -0800
Re: Opinion sought: Is this strictly conforming C? James Kuyper <jameskuyper@verizon.net> - 2018-02-15 22:15 -0500
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-16 08:44 -0800
Re: Opinion sought: Is this strictly conforming C? jameskuyper@verizon.net - 2018-02-16 11:47 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-16 13:00 -0800
Re: Opinion sought: Is this strictly conforming C? Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-19 12:25 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-19 13:21 -0800
Re: Opinion sought: Is this strictly conforming C? Randy Howard <rhoward.mx@EverybodyUsesIt.com> - 2018-02-19 15:26 -0600
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-19 13:59 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-19 14:38 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-19 15:21 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-19 15:59 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-19 17:11 -0800
Re: Opinion sought: Is this strictly conforming C? David Brown <david.brown@hesbynett.no> - 2018-02-20 09:17 +0100
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-20 07:58 -0800
Re: Opinion sought: Is this strictly conforming C? David Brown <david.brown@hesbynett.no> - 2018-02-20 18:21 +0100
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-20 09:25 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-20 11:52 -0800
Re: Opinion sought: Is this strictly conforming C? Richard Damon <Richard@Damon-Family.org> - 2018-02-20 22:27 -0500
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-20 23:07 -0800
Re: Opinion sought: Is this strictly conforming C? Manfred <noname@invalid.add> - 2018-02-21 14:07 +0100
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-21 09:02 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-21 09:50 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-21 12:46 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-21 13:09 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-21 15:15 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-21 15:51 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-21 17:06 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-21 17:46 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-22 00:18 -0800
Re: Opinion sought: Is this strictly conforming C? Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-21 22:14 -0800
Re: Opinion sought: Is this strictly conforming C? Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-21 11:39 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-21 14:59 -0800
Re: Opinion sought: Is this strictly conforming C? Richard Damon <Richard@Damon-Family.org> - 2018-02-21 22:14 -0500
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-22 00:50 -0800
Re: Opinion sought: Is this strictly conforming C? Richard Damon <Richard@Damon-Family.org> - 2018-02-22 07:22 -0500
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-22 12:40 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-22 13:00 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-22 13:48 -0800
Re: Opinion sought: Is this strictly conforming C? scott@slp53.sl.home (Scott Lurndal) - 2018-02-22 22:14 +0000
Re: Opinion sought: Is this strictly conforming C? Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-21 23:05 -0800
Re: Opinion sought: Is this strictly conforming C? Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-21 23:39 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-22 10:39 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-22 13:20 -0800
Re: Opinion sought: Is this strictly conforming C? asetofsymbols@gmail.com - 2018-02-23 00:30 -0800
Re: Opinion sought: Is this strictly conforming C? Manfred <noname@invalid.add> - 2018-02-16 20:05 +0100
Re: Opinion sought: Is this strictly conforming C? lee@ansync.com - 2018-02-16 11:14 -0800
Re: Opinion sought: Is this strictly conforming C? Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-19 11:30 -0800
Re: Opinion sought: Is this strictly conforming C? Steve Carroll <frelwizzen@gmail.com> - 2018-03-01 09:01 -0800
Re: Opinion sought: Is this strictly conforming C? Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-19 11:08 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-19 17:16 -0800
Re: Opinion sought: Is this strictly conforming C? Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-21 23:16 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-22 00:25 -0800
Re: Opinion sought: Is this strictly conforming C? Richard Damon <Richard@Damon-Family.org> - 2018-02-22 07:41 -0500
Re: Opinion sought: Is this strictly conforming C? Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-24 13:24 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-25 12:07 -0800
Re: Opinion sought: Is this strictly conforming C? Richard Damon <Richard@Damon-Family.org> - 2018-02-25 18:34 -0500
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-26 08:21 -0800
Re: Opinion sought: Is this strictly conforming C? Richard Damon <Richard@Damon-Family.org> - 2018-02-26 22:22 -0500
Re: Opinion sought: Is this strictly conforming C? David Brown <david.brown@hesbynett.no> - 2018-02-27 09:16 +0100
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-27 08:48 -0800
Re: Opinion sought: Is this strictly conforming C? David Brown <david.brown@hesbynett.no> - 2018-02-28 10:24 +0100
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-28 09:03 -0800
Re: Opinion sought: Is this strictly conforming C? David Brown <david.brown@hesbynett.no> - 2018-02-28 22:31 +0100
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-28 15:19 -0800
Re: Opinion sought: Is this strictly conforming C? David Brown <david.brown@hesbynett.no> - 2018-03-01 12:37 +0100
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-03-01 11:03 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-03-01 11:22 -0800
Re: Opinion sought: Is this strictly conforming C? Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-01 11:48 -0800
Re: Opinion sought: Is this strictly conforming C? Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-01 15:11 -0800
Re: Opinion sought: Is this strictly conforming C? Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-01 16:14 -0800
Re: Opinion sought: Is this strictly conforming C? Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-01 19:53 -0800
Re: Opinion sought: Is this strictly conforming C? Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-01 21:27 -0800
Re: Opinion sought: Is this strictly conforming C? Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-02 00:52 -0800
Re: Opinion sought: Is this strictly conforming C? Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-02 01:54 -0800
Re: Opinion sought: Is this strictly conforming C? Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-03 06:11 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-03-01 12:31 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-03-01 13:15 -0800
Re: Opinion sought: Is this strictly conforming C? Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-01 14:55 -0800
Re: Opinion sought: Is this strictly conforming C? Tim Rentsch <txr@alumni.caltech.edu> - 2018-03-03 02:19 -0800
Re: Opinion sought: Is this strictly conforming C? Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-03 03:03 -0800
Re: Opinion sought: Is this strictly conforming C? Keith Thompson <kst-u@mib.org> - 2018-02-25 15:36 -0800
Re: Opinion sought: Is this strictly conforming C? supercat@casperkitty.com - 2018-02-26 10:17 -0800
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