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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Pointers, constant values |
| Date | 2015-10-16 16:58 -0700 |
| Organization | None to speak of |
| Message-ID | <lnmvvi2wo1.fsf@kst-u.example.com> (permalink) |
| References | (7 earlier) <871tcur0gn.fsf@bsb.me.uk> <mvrpkd$qec$1@dont-email.me> <b3460f50-037e-4c93-87f5-58587d8e8374@googlegroups.com> <ln37xa4fi8.fsf@kst-u.example.com> <c7944465-bc6a-4740-9f19-e8dbf139c21c@googlegroups.com> |
supercat@casperkitty.com writes:
> On Friday, October 16, 2015 at 5:26:15 PM UTC-5, Keith Thompson wrote:
>> You can view a pointer as anything you like, but C has always viewed a
>> pointer of type FOO* as identifying an object of type FOO.
>
> Given:
> FOO foo;
> FOO *thing = malloc(1+3*sizeof (FOO));
> FOO *fp=thing;
> for (int i=0; i<3; i++)
> *fp++ = foo;
> /*******/
> unsigned char *cp = (unsigned char*) fp;
> *cp = 23;
>
> How would you describe the contents of "fp" at the line marked with the
> asterisks? I'd describe things by saying that "malloc" created an array
> of unsigned char, and that fp identifies a spot in that array. The
> contents of fp are not meaningless, and are indeed vital to the correct
> operation of the code, but it doesn't identify a "FOO" object nor even
> a place where one could be placed (unless sizeof(FOO) equals 1).
Sure, and a FOO* doesn't identify an object of type FOO if it's a null
pointer, or if it points just past the end of an array. The expression
*fp is still of type FOO, whatever contrived examples you use to show
that there doesn't have to be an object for it to point to.
[...]
--
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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Pointers, constant values Alla _ <modelling.data@gmail.com> - 2015-10-16 00:49 -0700
Re: Pointers, constant values Philip Lantz <prl@canterey.us> - 2015-10-16 01:49 -0700
Re: Pointers, constant values James Kuyper <jameskuyper@verizon.net> - 2015-10-16 09:41 -0400
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 08:55 -0700
Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 08:25 -0700
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 09:11 -0700
Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 12:06 -0700
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 12:55 -0700
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 17:49 +0100
Re: Pointers, constant values Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-10-16 13:23 -0400
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 19:34 +0100
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 12:05 -0700
Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 12:18 -0700
Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 12:13 -0700
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 20:33 +0100
Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 13:01 -0700
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 21:09 +0100
Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 13:41 -0700
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-16 21:07 +0100
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 21:20 +0100
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-16 22:02 +0100
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-16 22:21 +0100
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 14:39 -0700
Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 15:26 -0700
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 15:44 -0700
Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 16:58 -0700
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 17:28 -0700
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-16 22:50 +0100
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-16 15:14 -0700
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-17 01:23 +0100
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-17 19:39 +0100
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-17 22:42 +0100
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 00:31 +0100
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-18 02:11 +0100
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 11:59 +0100
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-18 12:12 +0100
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-18 12:28 +0100
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 23:16 +0100
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-18 23:34 +0100
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 01:45 +0100
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-19 11:51 +0100
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 12:55 +0100
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-19 13:51 +0100
Re: Pointers, constant values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-19 06:02 -0700
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-19 07:02 -0700
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-19 15:39 +0100
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-19 08:54 -0700
Re: Pointers, constant values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-19 09:14 -0700
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-19 10:21 -0700
Re: Pointers, constant values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-19 12:57 -0700
Re: Pointers, constant values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-19 21:20 +0000
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-20 20:50 -0700
Re: Pointers, constant values glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-21 04:58 +0000
Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-19 08:40 -0700
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 20:17 +0100
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-17 16:44 -0700
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 11:52 +0100
Re: Pointers, constant values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-18 05:15 -0700
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 21:54 +0100
Re: Pointers, constant values Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-18 16:09 -0700
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-18 07:55 -0700
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-18 21:47 +0100
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-18 15:37 -0700
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-19 00:10 +0100
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-18 19:04 -0700
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-16 21:13 +0100
Re: Pointers, constant values Ian Collins <ian-news@hotmail.com> - 2015-10-17 11:27 +1300
Re: Pointers, constant values Bartc <bc@freeuk.com> - 2015-10-17 00:56 +0100
Re: Pointers, constant values Les Cargill <lcargill99@comcast.com> - 2015-10-16 12:37 -0500
Re: Pointers, constant values James Kuyper <jameskuyper@verizon.net> - 2015-10-16 14:22 -0400
Re: Pointers, constant values Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-16 18:57 +0000
Re: Pointers, constant values Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-16 20:40 +0100
Re: Pointers, constant values Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-16 20:46 +0000
Re: Pointers, constant values Keith Thompson <kst-u@mib.org> - 2015-10-16 14:24 -0700
Re: Pointers, constant values Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-19 12:43 +0000
Re: Pointers, constant values Siri Cruz <chine.bleu@yahoo.com> - 2015-10-16 13:20 -0700
Re: Pointers, constant values supercat@casperkitty.com - 2015-10-17 13:59 -0700
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