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Groups > comp.lang.c > #104705
| From | Tim Rentsch <txr@alumni.caltech.edu> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: lvalues from the ternary op |
| Date | 2017-02-25 09:23 -0800 |
| Organization | A noiseless patient Spider |
| Message-ID | <kfn1sumrxpj.fsf@x-alumni2.alumni.caltech.edu> (permalink) |
| References | (15 earlier) <kfnzihhv2jq.fsf@x-alumni2.alumni.caltech.edu> <7cf3d284-16e8-4f6a-8f3a-b62b8fbcd9c5@googlegroups.com> <kfnlgsvtwax.fsf@x-alumni2.alumni.caltech.edu> <d74fd7b1-1dea-443d-8617-2be77c9b51ba@googlegroups.com> <lnfuj3ian8.fsf@kst-u.example.com> |
Keith Thompson <kst-u@mib.org> writes: > [...] One particular question > I'm curious about is whether the footnote in 6.5.2.3: > > If the member used to read the contents of a union object is > not the same as the member last used to store a value in the > object, the appropriate part of the object representation of > the value is reinterpreted as an object representation in the > new type as described in 6.2.6 (a process sometimes called > "type punning). This might be a trap representation. > > can be inferred from the normative wording of the standard. As I read the Standard this conclusion does follow from normative text, yes. (see next) > (It clearly represents the intent of the committee. The question > is whether that intent is sufficiently clearly stated in normative > text.) Some time ago I took the trouble to go through the relevant passages in the Standard to answer this question. Taking a comp.lang.c perspective (rather than a comp.std.c perspective or "language lawyer" perspective), I find no cause for doubt, in the same sense that I find no cause to doubt that a (char*)(void*) conversion of a pointer gives the same value as just (char*) does, or that storing an abstract value in an object and then reading the object using (unsigned char) gives bytes of the object representation of the abstract value stored (and vice versa). The Standard doesn't come right out and say either of those things, but everyone accepts them as true. My impression is that the same level of confidence applies for the union member access question. And I think most people would have that same impression, if they take the time to look at all the different relevant sections, and adopt the perspective outlined above. I'm not going to frame an argument to "make my case", I'm just stating my thoughts on the matter. But if someone else goes through the exercise I'd be interested to hear their comments, and would be happy to discuss and compare their reactions with mine if that can be done in a non-argumentative way.
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Re: lvalues from the ternary op Manfred <noname@invalid.add> - 2017-01-04 19:46 +0100
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-04 11:08 -0800
Re: lvalues from the ternary op Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-04 21:10 +0000
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-04 13:48 -0800
Re: lvalues from the ternary op Ian Collins <ian-news@hotmail.com> - 2017-01-05 11:07 +1300
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-04 14:20 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-04 14:41 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-04 15:21 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-04 15:52 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-04 16:37 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-04 18:31 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-13 17:26 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-13 17:49 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-15 22:53 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-13 17:08 -0800
Re: lvalues from the ternary op Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-14 02:15 +0000
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-15 22:51 -0800
Re: lvalues from the ternary op luser droog <luser.droog@gmail.com> - 2017-01-16 23:09 -0800
Re: lvalues from the ternary op Manfred <noname@invalid.add> - 2017-01-18 14:51 +0100
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-18 09:59 -0800
Re: lvalues from the ternary op Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2017-01-18 13:12 -0500
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-18 12:11 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-18 12:45 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-18 14:07 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-18 14:40 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-18 16:10 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-18 18:08 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-19 06:44 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-19 08:40 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-19 12:32 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-20 06:01 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-20 08:15 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-20 10:51 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-20 11:32 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-20 13:41 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-23 07:04 -0800
Re: lvalues from the ternary op Ike Naar <ike@iceland.freeshell.org> - 2017-01-23 17:59 +0000
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-23 10:57 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-31 08:45 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-01-31 09:13 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-31 10:17 -0800
Re: lvalues from the ternary op Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-01 01:51 +0000
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-01 14:24 -0800
Re: lvalues from the ternary op Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-02-02 03:07 +0000
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-04 04:43 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-04 08:01 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-09 09:06 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-09 11:56 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-12 10:29 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-12 13:43 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-19 21:44 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-20 08:15 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-24 07:58 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-24 10:00 -0800
Re: lvalues from the ternary op scott@slp53.sl.home (Scott Lurndal) - 2017-02-24 18:58 +0000
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-24 13:03 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-02-24 14:11 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-02-24 12:42 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-02-24 13:49 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-24 13:58 -0800
Re: lvalues from the ternary op Keith Thompson <kst-u@mib.org> - 2017-02-24 14:56 -0800
Re: lvalues from the ternary op supercat <flatfinger@casperkitty.com> - 2017-02-25 14:00 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-25 09:23 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-25 09:43 -0800
Re: lvalues from the ternary op Kelsey Bjarnason <kbjarnason@gmail.com> - 2017-02-01 22:47 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-02 10:12 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-04 07:51 -0800
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-02-04 08:18 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-09 08:58 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-04 04:00 -0800
Re: lvalues from the ternary op Kelsey Bjarnason <kbjarnason@gmail.com> - 2017-02-04 09:35 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-04 09:35 -0800
Re: lvalues from the ternary op Robert Wessel <robertwessel2@yahoo.com> - 2017-01-31 13:36 -0600
Re: lvalues from the ternary op supercat@casperkitty.com - 2017-01-31 12:23 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-01 13:48 -0800
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-31 08:53 -0800
Re: lvalues from the ternary op Manfred <noname@invalid.add> - 2017-01-19 14:10 +0100
Re: lvalues from the ternary op Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-30 12:05 -0800
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