Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.lang.c++ > #44730
| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: This will work or not? |
| Date | 2016-09-02 12:37 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <87wpiu4jny.fsf@bsb.me.uk> (permalink) |
| References | (8 earlier) <f73fed95-d4c0-4145-810b-4db6e2b1f4f7@googlegroups.com> <nqaj10$mv2$1@jstuckle.eternal-september.org> <a86af030-51bd-42d4-bc60-ae4be6f6ab0f@googlegroups.com> <nqbhfb$12q1$1@gioia.aioe.org> <nqbk65$bmh$1@dont-email.me> |
David Brown <david.brown@hesbynett.no> writes:
> On 02/09/16 11:41, Manfred wrote:
>> On 9/2/2016 4:02 AM, me wrote:
<snip>
>>> The standard also says that the as-if rule over-rides everything else in
>>> the standard, and that only observable behaviour of the program need be
>>> considered. So again, why is structure member layout _different_ in this
>>> respect?
>>>
>> It is different because of the presence of the union.
>> When you access the struct memory area through the array you are
>> accessing data in a well-specified order, and the struct members must
>> therefore follow the order specified by the standard.
>> As long as memory access is legal, and it is in this case, if
>> optimization could reorder the struct members, the "as-if" rule would be
>> violated because the optimized and non-optimized code results would be
>> different.
>
> The as-if rule still applies. If we stick to C, where you /are/ allowed
> to access data in different ways with a union, we could have this:
>
> union {
> struct {
> uint32_t a;
> uint32_t b;
> uint64_t c;
> uint32_t d;
> };
> uint32_t as_array[5];
> } u;
Is the 5 a typo?
> When you write:
>
> uint32_t foo(void) {
> u.d = 123;
> u.b = u.as_array[4];
> return u.as_array[1];
> }
Is the 4 a typo?
> The compiler will have to return 123. It must /behave/ in this way.
I've not been following the details, so maybe there are some assumptions
in play here, but if the struct has unknown padding the only thing you
can rely on is that u.a and u.as_array[0] overlap.
<snip>
--
Ben.
Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
This will work or not? Melzzzzz <mel@zzzzz.com> - 2016-08-31 14:59 +0200
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-08-31 15:20 +0200
Re: This will work or not? mark <mark@invalid.invalid> - 2016-08-31 16:05 +0200
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-08-31 16:19 +0200
Re: This will work or not? scott@slp53.sl.home (Scott Lurndal) - 2016-08-31 14:20 +0000
Re: This will work or not? Bo Persson <bop@gmb.dk> - 2016-08-31 18:53 +0200
Re: This will work or not? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-01 09:03 -0700
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-01 22:45 +0200
Re: This will work or not? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-01 18:08 -0700
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-02 09:24 +0200
Re: This will work or not? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-04 06:31 -0700
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-04 20:19 +0200
Re: This will work or not? Manfred <noname@invalid.add> - 2016-08-31 15:45 +0200
Re: This will work or not? Melzzzzz <mel@zzzzz.com> - 2016-08-31 15:59 +0200
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-08-31 16:22 +0200
Re: This will work or not? Manfred <noname@invalid.add> - 2016-08-31 17:06 +0200
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-08-31 19:29 +0200
Re: This will work or not? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2016-08-31 21:52 +0100
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-01 09:07 +0200
Re: This will work or not? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2016-09-01 12:30 +0100
Re: This will work or not? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-01 09:01 -0700
Re: This will work or not? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2016-09-01 18:16 +0100
Re: This will work or not? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-01 18:37 -0700
Re: This will work or not? Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2016-09-02 10:42 +0100
Re: This will work or not? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-04 06:59 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-08-31 23:17 -0400
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-01 09:35 +0200
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-01 15:34 -0400
Re: This will work or not? me <crisdunbar@gmail.com> - 2016-09-01 13:50 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-01 21:01 -0400
Re: This will work or not? me <crisdunbar@gmail.com> - 2016-09-01 19:02 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-01 22:17 -0400
Re: This will work or not? me <crisdunbar@gmail.com> - 2016-09-02 08:19 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-02 12:39 -0400
Re: This will work or not? me <crisdunbar@gmail.com> - 2016-09-02 12:26 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-02 16:38 -0400
Re: This will work or not? me <crisdunbar@gmail.com> - 2016-09-02 13:51 -0700
Re: This will work or not? me <crisdunbar@gmail.com> - 2016-09-02 14:16 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-02 19:58 -0400
Re: This will work or not? Paavo Helde <myfirstname@osa.pri.ee> - 2016-09-02 23:56 +0300
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-03 17:58 +0200
Re: This will work or not? Manfred <noname@invalid.add> - 2016-09-02 11:41 +0200
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-02 12:27 +0200
Re: This will work or not? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-02 12:37 +0100
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-02 17:39 +0200
Re: This will work or not? Melzzzzz <mel@zzzzz.com> - 2016-09-02 17:40 +0200
Re: This will work or not? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-02 16:54 +0100
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-02 20:22 +0200
Re: This will work or not? Richard Damon <Richard@Damon-Family.org> - 2016-09-02 08:04 -0400
Re: This will work or not? BartC <bc@freeuk.com> - 2016-09-02 13:51 +0100
Re: This will work or not? Richard Damon <Richard@Damon-Family.org> - 2016-09-02 21:48 -0400
Re: This will work or not? Manfred <noname@invalid.add> - 2016-09-02 15:17 +0200
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-02 17:46 +0200
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-01 23:14 +0200
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-01 21:02 -0400
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-02 09:35 +0200
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-02 08:50 -0400
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-02 17:59 +0200
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-02 12:49 -0400
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-02 20:36 +0200
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-02 16:32 -0400
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-03 18:08 +0200
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-03 18:25 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-03 23:51 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-03 21:48 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-04 03:48 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-03 23:05 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-04 05:02 +0100
Re: This will work or not? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-04 10:57 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 09:40 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-04 16:39 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 12:46 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-04 17:51 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 13:07 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-04 18:37 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 17:16 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-04 22:23 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 18:54 -0400
Re: This will work or not? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-09-04 09:58 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 13:08 -0400
Re: This will work or not? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-09-04 10:21 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 17:18 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-04 22:24 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 18:56 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-05 00:27 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 22:53 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-05 18:18 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-05 15:27 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-05 20:32 +0100
Re: This will work or not? woodbrian77@gmail.com - 2016-09-05 14:07 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-05 18:15 -0400
Re: This will work or not? Ike Naar <ike@iceland.freeshell.org> - 2016-09-05 20:12 +0000
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-05 22:05 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-05 18:16 -0400
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-06 08:47 +0200
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-06 09:12 -0400
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-06 16:31 +0200
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-06 11:20 -0400
Re: This will work or not? bighe.trole@gmail.com - 2016-09-04 18:55 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 22:55 -0400
Re: This will work or not? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-09-04 17:17 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 22:57 -0400
Re: This will work or not? "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-09-05 11:20 -0700
Re: This will work or not? Luuk <luuk@invalid.lan> - 2016-09-04 18:54 +0200
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-04 17:59 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 13:08 -0400
Re: This will work or not? David Brown <david.brown@hesbynett.no> - 2016-09-04 20:25 +0200
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 17:20 -0400
Re: This will work or not? Öö Tiib <ootiib@hot.ee> - 2016-09-04 02:36 -0700
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-04 09:41 -0400
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-03 21:49 -0400
Re: This will work or not? Mr Flibble <flibbleREMOVETHISBIT@i42.co.uk> - 2016-09-04 03:49 +0100
Re: This will work or not? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-03 23:06 -0400
Re: This will work or not? woodbrian77@gmail.com - 2016-09-03 21:16 -0700
Re: This will work or not? Vir Campestris <vir.campestris@invalid.invalid> - 2016-08-31 21:08 +0100
Re: This will work or not? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2016-09-01 02:28 +0200
Re: This will work or not? Öö Tiib <ootiib@hot.ee> - 2016-09-01 01:28 -0700
Re: This will work or not? "Chris M. Thomasson" <invalid@invalid.invalid> - 2016-09-02 12:06 -0700
Re: This will work or not? Öö Tiib <ootiib@hot.ee> - 2016-09-05 02:21 -0700
Re: This will work or not? Melzzzzz <mel@zzzzz.com> - 2016-09-05 13:38 +0200
Re: This will work or not? Juha Nieminen <nospam@thanks.invalid> - 2016-09-05 11:34 +0000
Re: This will work or not? Melzzzzz <mel@zzzzz.com> - 2016-09-05 13:36 +0200
Re: This will work or not? Vir Campestris <vir.campestris@invalid.invalid> - 2016-09-05 21:25 +0100
csiph-web