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| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Objective C |
| Date | 2015-11-19 22:13 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <87bnaptz7w.fsf@bsb.me.uk> (permalink) |
| References | (15 earlier) <7c4f687f-742c-4adb-8639-d8fc95a9b78a@googlegroups.com> <87mvuavm69.fsf@bsb.me.uk> <4f1444ba-a9e9-42bc-9d43-bc29b1a076c2@googlegroups.com> <87r3jmt6ac.fsf@bsb.me.uk> <63c43be8-de88-4f9c-b24c-9566243b0dc3@googlegroups.com> |
supercat@casperkitty.com writes:
> On Thursday, November 19, 2015 at 8:26:03 AM UTC-6, Ben Bacarisse wrote:
>> supercat writes:
>>
>> > On Wednesday, November 18, 2015 at 6:59:50 PM UTC-6, Ben Bacarisse wrote:
>> >> > When test1 is called from main, what would be the effective
>> >> > type of *fp and
>> >> > *ip?
>> >>
>> >> They both are accesses to the same object whose declared type is the
>> >> union.
>> >
>> > A pointer to a union type, suitably converted, points to each of its
>> > members (N1256 6.7.2.1 13).
>>
>> Not sure I see the relevance...
>
>> > Would it be legal to say:
>> >
>> > union { int i; float f; } flint;
>> > scanf("%d", &flint.i);
>> >
>> > if nothing ever accessed flint.f?
>>
>> Yes, it would. Why do you think it might not be?
>
> I was confused for the longest time by the belief that it was legal, but
> recognizing that it isn't makes things a lot clearer.
>
> Were it not for the provision in N1570 6.5.7 which mentions unions, it would
> be illegal to access union members in any way whatsoever (which obviously
> wouldn't be useful); the only thing which is authorized by that section is
> accessing members of the union through an lvalue of the union type (as would
> be done with "flint.i=123;"). The call to scanf does not cause flint to be
> modified using an lvalue of type "flint"; it causes it to be modified with an
> lvalue of type "int", and in the process illegitimately modifies
> flint.f.
Why would you read it like that? If that argument were valid, flint.i =
42; would be undefined because flint would be accessed through an lvalue
of type int rather than one with the union type. Clearly that is not
the intent. flint.i = 42; is access to an object of type int and it is
done though an lvalue with teh declared type of that object (int).
Now, you can argue that this should be clearer; you can say that more
needs to be said about union, objects and accesses, but there can't be
any doubt that a reading which prevents flint.i = 42 because is
illegitimately modifies flint.f can't be right.
--
Ben.
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Objective C Alla _ <modelling.data@gmail.com> - 2015-11-10 09:10 -0800
Re: Objective C "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-10 09:16 -0800
Re: Objective C Richard Heathfield <rjh@cpax.org.uk> - 2015-11-10 17:17 +0000
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-10 09:32 -0800
Re: Objective C Mark Storkamp <mstorkamp@yahoo.com> - 2015-11-10 11:38 -0600
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-10 12:36 -0500
Re: Objective C Alla _ <modelling.data@gmail.com> - 2015-11-10 11:15 -0800
Re: Objective C Richard Heathfield <rjh@cpax.org.uk> - 2015-11-10 21:51 +0000
Re: Objective C Alla _ <modelling.data@gmail.com> - 2015-11-10 23:13 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-13 16:01 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-14 01:07 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-14 06:26 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-14 22:22 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-14 15:46 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 01:47 +0000
Re: Objective C BartC <bc@freeuk.com> - 2015-11-15 10:43 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-15 13:19 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-14 15:43 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-15 23:50 +0100
Re: Objective C gazelle@shell.xmission.com (Kenny McCormack) - 2015-11-16 00:05 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-15 19:10 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-16 09:11 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-16 11:57 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-16 20:38 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-16 13:20 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-16 22:28 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-16 15:33 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-16 15:56 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-17 01:43 +0000
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-17 01:21 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-16 18:11 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-16 20:12 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 00:59 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-18 22:46 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 14:25 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-19 07:58 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 22:13 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-19 15:29 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 08:44 -0800
Re: Objective C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-17 01:26 +0000
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-16 21:48 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-16 20:27 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-17 13:58 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-17 12:28 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-18 13:00 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-18 12:31 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-18 16:43 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-18 15:57 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-19 19:09 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-19 19:05 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-20 15:00 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-20 15:30 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 17:11 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-22 15:53 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-23 13:51 -0600
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-24 12:00 +0000
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-17 10:26 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-17 06:20 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-17 16:41 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-17 12:08 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-17 16:27 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-17 14:55 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-18 13:59 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-18 13:06 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-24 14:24 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-24 15:11 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-26 17:02 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-27 07:26 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-18 21:56 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 02:17 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-22 07:16 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-26 17:11 -0600
Re: Objective C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-22 19:09 +0000
Re: Objective C Robert Wessel <robertwessel2@yahoo.com> - 2015-11-17 23:28 -0600
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-18 15:33 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-18 23:06 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-19 09:12 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-19 09:25 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-19 21:06 +0100
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-20 13:49 -0800
Re: Objective C Robert Wessel <robertwessel2@yahoo.com> - 2015-11-21 05:01 -0600
Re: Objective C Robert Wessel <robertwessel2@yahoo.com> - 2015-11-21 05:09 -0600
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-21 03:31 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-21 17:43 -0600
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-21 16:00 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 01:12 -0600
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-27 16:42 +0000
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-27 12:38 -0500
Re: Objective C supercat@casperkitty.com - 2015-11-27 11:09 -0800
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-21 19:06 -0500
Re: Objective C supercat@casperkitty.com - 2015-11-21 17:00 -0800
Re: Objective C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-22 14:44 +0000
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 01:55 -0600
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-22 00:03 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-22 10:18 +0000
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 03:21 -0800
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-22 10:53 -0500
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 20:28 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-22 18:52 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-23 11:58 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-23 15:24 -0800
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-23 09:46 -0500
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-23 08:13 -0800
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-23 12:04 -0500
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-23 11:52 -0600
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 16:05 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-24 09:09 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-12-08 08:48 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-12-08 10:40 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-12-09 12:34 -0800
Re: Objective C supercat@casperkitty.com - 2015-12-08 10:50 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-12-09 12:42 -0800
Re: Objective C supercat@casperkitty.com - 2015-12-09 13:38 -0800
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-12-10 19:54 +0000
Re: Objective C David Thompson <dave.thompson2@verizon.net> - 2015-12-06 08:02 -0500
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-22 14:36 -0800
Re: Objective C Robert Wessel <robertwessel2@yahoo.com> - 2015-11-23 00:41 -0600
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 07:39 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-22 14:23 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-17 10:24 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-18 15:40 +0100
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-20 16:02 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-21 15:53 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-21 08:58 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-22 22:14 +0100
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 03:39 -0800
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-23 13:24 +0000
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-26 09:39 -0800
Re: Objective C Robert Wessel <robertwessel2@yahoo.com> - 2015-11-26 13:16 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-26 12:25 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 14:34 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-26 12:39 -0800
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-27 16:43 +0000
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-27 09:29 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 14:18 -0800
Re: Objective C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-23 22:35 +0000
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-23 17:40 -0500
Re: Objective C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-24 05:35 +0000
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-25 12:15 -0800
Re: Objective C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-25 22:49 +0000
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-27 16:44 +0000
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 14:03 -0800
Re: Objective C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-29 09:29 +0000
Re: Objective C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-22 19:01 +0000
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 07:31 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-23 07:43 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-23 08:17 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-23 17:34 +0100
Re: Objective C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-23 22:02 +0000
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-24 10:12 +0100
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 08:39 -0800
Re: Objective C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-14 18:24 +0000
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-14 12:23 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-14 12:36 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-14 13:13 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-14 14:04 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-14 14:15 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-14 14:29 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-14 15:39 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-14 16:37 -0800
Re: Objective C Ian Collins <ian-news@hotmail.com> - 2015-11-15 13:46 +1300
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 02:06 +0000
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-15 03:25 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 12:56 +0000
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-15 07:53 -0600
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-15 07:19 -0600
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 13:29 +0000
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-15 10:56 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-15 14:35 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-15 16:52 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-15 19:49 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-16 11:02 +0000
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-16 10:36 -0800
Re: Objective C David Thompson <dave.thompson2@verizon.net> - 2015-12-06 08:03 -0500
Re: Objective C Melzzzzz <mel@zzzzz.com> - 2015-11-16 02:01 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-15 19:34 -0800
Re: Objective C Chad <cdalten@gmail.com> - 2015-11-15 19:54 -0800
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-17 22:36 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-17 15:27 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-17 21:15 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-14 22:08 +0000
Re: Objective C fir <profesor.fir@gmail.com> - 2015-11-27 14:36 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-10 19:03 +0100
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-10 10:50 -0800
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