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Groups > comp.lang.c > #126991
| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Opinion sought: Is this strictly conforming C? |
| Date | 2018-02-22 10:39 -0800 |
| Organization | None to speak of |
| Message-ID | <lneflclvh7.fsf@kst-u.example.com> (permalink) |
| References | (1 earlier) <p65ibn$par$1@dont-email.me> <29e38fdf-86ef-4935-891a-b2683ee99b88@googlegroups.com> <kfnfu5wwwun.fsf@x-alumni2.alumni.caltech.edu> <42bf72ce-89a8-405e-9155-9fbebe4b6d31@googlegroups.com> <kfnvaeptqwb.fsf@x-alumni2.alumni.caltech.edu> |
Tim Rentsch <txr@alumni.caltech.edu> writes:
[...]
> Last but not least, the text change you mention didn't happen
> as part of C99, but much earlier, as part of a response to
> a Defect Report filed in 1992:
>
> http://www.open-std.org/JTC1/SC22/WG14/www/docs/dr_017.html
>
> The response makes clear that the new text is a clarification of
> the intended meaning, not a rule change.
It's question 16 (of 39) in the cited DR.
Question 16
Pointer to multidimensional array
Given the declaration:
char a[3][4], (*p)[4]=a[1];
Does the behavior become undefined when:
1. p no longer points within the slice of the array, or
2. p no longer points within the object a?
This case should be explicitly stated.
Arguments for/against:
The standard refers to a pointed-to object. There does not
appear to be any concept of a slice of an array being an
independent object.
Response
For an array of arrays, the permitted pointer arithmetic in
subclause 6.3.6, page 47, lines 12-40 is to be understood
by interpreting the use of the word ``object'' as denoting
the specific object determined directly by the pointer's
type and value, not other objects related to that one
by contiguity. Therefore, if an expression exceeds these
permissions, the behavior is undefined. For example, the
following code has undefined behavior:
int a[4][5];
a[1][7] = 0; /* undefined */
Some conforming implementations may choose to diagnose an "array
bounds violation," while others may choose to interpret such
attempted accesses successfully with the "obvious" extended
semantics.
Correction
Add to subclause G.2, page 201:
- An array subscript is out of range, even if an object is
apparently accessible with the given subscript (as in the lvalue
expression a[1][7] given the declaration int a[4][5]) (6.3.6).
--
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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