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Groups > comp.lang.c > #122722
| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Equal yet different pointers |
| Date | 2017-11-16 08:55 -0800 |
| Organization | None to speak of |
| Message-ID | <87k1yqyxgx.fsf@kst-u.example.com> (permalink) |
| References | <pointers-20171116105459@ram.dialup.fu-berlin.de> <oujpb3$b9s$1@dont-email.me> <elePB.43928$WQ.6569@fx10.am4> <ouk4q6$ql4$1@dont-email.me> |
David Brown <david.brown@hesbynett.no> writes:
[...]
>>> On 16/11/17 11:00, Stefan Ram wrote:
>>>> I did not invent this program, I just read it in an article
>>>> and then typed it in from my memory:
>>>>
>>>> main.c
>>>>
>>>> #include <stdio.h>
>>>> #include <string.h>
>>>>
>>>> int main()
>>>> { int i = 1; int j = 2;
>>>> int * p = &i + 1; int * q = &j;
>>>> if( !memcmp( &p, &q, sizeof( p )))
>>>> { *p = 3; printf( "%d %d\n", *p, *q ); }}
>>>>
>>>> transcript
>>>>
>>>> 3 2
[...]
> gcc /does/ do something wrong here - it accepts this program without
> warnings, even with -Wall -Wextra. So I do have something to complain
> about here with gcc.
Why do you expect a warning? There may or may not be undefined
behavior, but as far as I can tell no diagnostic is required.
For example,
int *p = &i = 1;
is valid; the object i can be treated as a single element array, and p
points just past the end of it. Normally dereferencing p would have
undefined behavior (which a compiler could detect only if it does data
flow analysis).
I'll have more to say in a followup to the original post.
--
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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Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-16 11:29 +0100
Re: Equal yet different pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-11-16 03:01 -0800
Re: Equal yet different pointers "Bill Davy" <Bill@XchelSys.co.uk> - 2017-11-16 11:03 +0000
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-16 13:55 +0100
Re: Equal yet different pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-11-16 06:44 -0800
Re: Equal yet different pointers Spiros Bousbouras <spibou@gmail.com> - 2017-11-16 14:49 +0000
Re: Equal yet different pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-11-16 08:28 -0800
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-16 16:46 +0100
Re: Equal yet different pointers "James R. Kuyper" <jameskuyper@verizon.net> - 2017-11-16 12:29 -0500
Re: Equal yet different pointers Nick Bowler <nbowler@draconx.ca> - 2017-11-17 22:47 +0000
Re: Equal yet different pointers Richard Damon <Richard@Damon-Family.org> - 2017-11-18 17:03 -0500
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-16 11:09 +0000
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-16 11:14 +0000
Re: Equal yet different pointers "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-11-16 03:41 -0800
Rick's neuroses (Was: Equal yet different pointers) gazelle@shell.xmission.com (Kenny McCormack) - 2017-11-16 12:11 +0000
Re: Rick's neuroses (Was: Equal yet different pointers) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-11-16 04:30 -0800
Re: Rick's neuroses (Was: Equal yet different pointers) David Brown <david.brown@hesbynett.no> - 2017-11-16 14:52 +0100
Obscure references (Was: Rick's neuroses (Was: Equal yet different pointers)) gazelle@shell.xmission.com (Kenny McCormack) - 2017-11-19 12:32 +0000
Re: Obscure references Noob <root@127.0.0.1> - 2017-11-20 11:08 +0100
Re: Obscure references David Brown <david.brown@hesbynett.no> - 2017-11-20 12:36 +0100
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-16 14:45 +0100
Re: Equal yet different pointers Keith Thompson <kst-u@mib.org> - 2017-11-16 08:55 -0800
Re: Equal yet different pointers Spiros Bousbouras <spibou@gmail.com> - 2017-11-16 17:09 +0000
Re: Equal yet different pointers Keith Thompson <kst-u@mib.org> - 2017-11-16 09:33 -0800
Re: Equal yet different pointers Gareth Owen <gwowen@gmail.com> - 2017-11-16 19:20 +0000
Re: Equal yet different pointers Keith Thompson <kst-u@mib.org> - 2017-11-16 11:36 -0800
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-16 22:50 +0100
Re: Equal yet different pointers supercat@casperkitty.com - 2017-11-16 14:34 -0800
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-17 10:44 +0100
Re: Equal yet different pointers supercat@casperkitty.com - 2017-11-17 08:23 -0800
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-17 19:13 +0100
Re: Equal yet different pointers supercat@casperkitty.com - 2017-11-17 16:45 -0800
Re: Equal yet different pointers Spiros Bousbouras <spibou@gmail.com> - 2017-11-18 07:30 +0000
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-16 22:25 +0100
Re: Equal yet different pointers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-11-16 23:11 +0000
Re: Equal yet different pointers supercat@casperkitty.com - 2017-11-16 15:47 -0800
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-17 10:49 +0100
Re: Equal yet different pointers Gareth Owen <gwowen@gmail.com> - 2017-11-16 19:20 +0000
Re: Equal yet different pointers "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-11-16 11:26 -0800
Re: Equal yet different pointers gazelle@shell.xmission.com (Kenny McCormack) - 2017-11-16 22:22 +0000
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-16 23:09 +0000
Re: Equal yet different pointers gazelle@shell.xmission.com (Kenny McCormack) - 2017-11-17 08:50 +0000
Re: Equal yet different pointers Gareth Owen <gwowen@gmail.com> - 2017-11-17 17:42 +0000
Re: Equal yet different pointers gazelle@shell.xmission.com (Kenny McCormack) - 2017-11-17 19:35 +0000
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-16 23:34 +0000
Re: Equal yet different pointers supercat@casperkitty.com - 2017-11-16 15:58 -0800
Re: Equal yet different pointers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-11-17 00:57 +0000
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-17 12:32 +0100
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-17 12:31 +0000
Re: Equal yet different pointers mark.bluemel@gmail.com - 2017-11-17 07:23 -0800
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-17 17:14 +0100
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-18 00:12 +0000
Re: Equal yet different pointers Ian Collins <ian-news@hotmail.com> - 2017-11-18 13:39 +1300
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-18 01:39 +0000
Re: Equal yet different pointers Ian Collins <ian-news@hotmail.com> - 2017-11-18 14:42 +1300
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-18 02:01 +0000
Re: Equal yet different pointers Melzzzzz <Melzzzzz@zzzzz.com> - 2017-11-18 02:07 +0000
Re: Equal yet different pointers Ian Collins <ian-news@hotmail.com> - 2017-11-18 15:35 +1300
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-18 11:23 +0000
Re: Equal yet different pointers Ian Collins <ian-news@hotmail.com> - 2017-11-19 12:02 +1300
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-18 23:25 +0000
Re: Equal yet different pointers Ian Collins <ian-news@hotmail.com> - 2017-11-19 13:44 +1300
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-19 01:05 +0000
Re: Equal yet different pointers Ian Collins <ian-news@hotmail.com> - 2017-11-19 14:30 +1300
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-19 01:48 +0000
Re: Equal yet different pointers Ian Collins <ian-news@hotmail.com> - 2017-11-19 16:21 +1300
Re: Equal yet different pointers Reinhardt Behm <rbehm@hushmail.com> - 2017-11-19 11:44 +0800
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-19 10:10 +0000
Re: Equal yet different pointers mark.bluemel@gmail.com - 2017-11-20 00:52 -0800
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-19 23:27 +0100
Re: Equal yet different pointers Richard Damon <Richard@Damon-Family.org> - 2017-11-19 22:48 -0500
Re: Equal yet different pointers Ian Collins <ian-news@hotmail.com> - 2017-11-20 16:52 +1300
Re: Equal yet different pointers Spiros Bousbouras <spibou@gmail.com> - 2017-11-16 14:28 +0000
Re: Equal yet different pointers Barry Schwarz <schwarzb@dqel.com> - 2017-11-16 07:10 -0800
Re: Equal yet different pointers David Brown <david.brown@hesbynett.no> - 2017-11-16 16:51 +0100
Re: Equal yet different pointers "James R. Kuyper" <jameskuyper@verizon.net> - 2017-11-16 12:57 -0500
Re: Equal yet different pointers supercat@casperkitty.com - 2017-11-16 08:03 -0800
Re: Equal yet different pointers "James R. Kuyper" <jameskuyper@verizon.net> - 2017-11-16 12:38 -0500
Re: Equal yet different pointers "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-16 20:13 +0100
Re: Equal yet different pointers "James R. Kuyper" <jameskuyper@verizon.net> - 2017-11-16 14:29 -0500
Re: Equal yet different pointers Jorgen Grahn <grahn+nntp@snipabacken.se> - 2017-11-16 15:57 +0000
Re: Equal yet different pointers Spiros Bousbouras <spibou@gmail.com> - 2017-11-16 16:07 +0000
Re: Equal yet different pointers Jorgen Grahn <grahn+nntp@snipabacken.se> - 2017-11-16 19:01 +0000
Re: Equal yet different pointers Spiros Bousbouras <spibou@gmail.com> - 2017-11-16 19:14 +0000
Re: Equal yet different pointers Jorgen Grahn <grahn+nntp@snipabacken.se> - 2017-11-16 19:47 +0000
Re: Equal yet different pointers bartc <bc@freeuk.com> - 2017-11-16 23:08 +0000
Re: Equal yet different pointers Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-11-17 00:33 +0000
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