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| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: sizeof(arr[0]) |
| Date | 2015-06-10 21:21 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <87381z8gbq.fsf@bsb.me.uk> (permalink) |
| References | <5c0c353e-3650-4ab7-a956-0ddfc39b0507@googlegroups.com> |
kuznecov.alexey@gmail.com writes: > There is a well know pattern of figuring out array length: > int arr[10]; > size_t len = sizeof(arr) / sizeof(arr[0]); > assert(len == 10); > > This pattern applies to static arrays and auto arrays of constant > size. It also applies to variable length arrays in C99. > > I want to apply similar idea for figuring out dynamic array size in bytes: > size_t known_len = 10; > int *ptr = malloc(known_len); > size_t size = known_len * sizeof(ptr[0]); > assert(size == known_len * sizeof(int)); I don't know what this is supposed to do. The main problem I see is that the malloc call asks for less memory than you seem to need. A common idiom is int *ptr = malloc(known_len * sizeof *ptr); Maybe you intended to write that, but then I don't know what all the rest is about... (And remember to check that the allocation succeeded!) <snip> > My questions are: > - Can the expression "sizeof(ptr[0])" be used in the code when type > of ptr is known and the value of ptr is not known? Yes, the operand of sizeof is not evaluated in this case. > - Can such use be justified according to C99 standard? GNU GCC spec? It's standard C99 and C11 (6.5.2.4 p2). -- Ben.
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sizeof(arr[0]) kuznecov.alexey@gmail.com - 2015-06-10 12:38 -0700
Re: sizeof(arr[0]) James Kuyper <jameskuyper@verizon.net> - 2015-06-10 16:00 -0400
Re: sizeof(arr[0]) kuznecov.alexey@gmail.com - 2015-06-10 14:53 -0700
Re: sizeof(arr[0]) kuznecov.alexey@gmail.com - 2015-06-10 13:11 -0700
Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-10 21:21 +0100
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-10 22:08 +0100
Re: sizeof(arr[0]) Andrew Cooper <amc96@cam.ac.uk> - 2015-06-11 00:27 +0100
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-11 00:34 +0100
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-11 00:38 +0100
Re: writing code for people who don't know the language (was: sizeof(arr[0])) Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-06-10 21:16 -0400
Re: writing code for people who don't know the language Richard Heathfield <rjh@cpax.org.uk> - 2015-06-11 02:35 +0100
Re: writing code for people who don't know the language Bartc <bc@freeuk.com> - 2015-06-11 11:16 +0100
Re: writing code for people who don't know the language Bartc <bc@freeuk.com> - 2015-06-11 11:29 +0100
Re: writing code for people who don't know the language gazelle@shell.xmission.com (Kenny McCormack) - 2015-06-11 11:43 +0000
Re: sizeof(arr[0]) Paul N <gw7rib@aol.com> - 2015-06-14 13:13 -0700
Re: sizeof(arr[0]) Philip Lantz <prl@canterey.us> - 2015-06-14 17:52 -0700
Re: sizeof(arr[0]) "Bill Cunningham" <nospam@nspam.invalid> - 2015-06-15 14:26 -0400
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-15 19:34 +0100
Re: sizeof(arr[0]) "Bill Cunningham" <nospam@nspam.invalid> - 2015-06-15 14:55 -0400
Re: sizeof(arr[0]) Melzzzzz <melz@zzzzz.com> - 2015-06-15 20:59 +0200
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-15 20:11 +0100
Re: sizeof(arr[0]) "Bill Cunningham" <nospam@nspam.invalid> - 2015-06-15 15:22 -0400
Re: sizeof(arr[0]) David Kleinecke <dkleinecke@gmail.com> - 2015-06-16 09:51 -0700
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 10:51 -0700
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 19:14 +0100
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 11:43 -0700
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 20:03 +0100
Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-16 19:15 +0100
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 11:34 -0700
Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-16 20:28 +0100
Re: sizeof(arr[0]) James Kuyper <jameskuyper@verizon.net> - 2015-06-16 15:42 -0400
Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 13:35 -0700
Re: sizeof(arr[0]) James Kuyper <jameskuyper@verizon.net> - 2015-06-16 16:59 -0400
Re: sizeof(arr[0]) Dr Nick <nospam-4@temporary-address.org.uk> - 2015-06-16 22:05 +0100
Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 14:27 -0700
Re: sizeof(arr[0]) Dr Nick <nospam-4@temporary-address.org.uk> - 2015-06-17 07:07 +0100
Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-17 01:22 +0100
Re: sizeof(arr[0]) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-06-16 19:45 +0000
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 13:03 -0700
Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-17 10:58 +0100
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 05:58 -0700
Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-17 15:46 +0100
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 08:14 -0700
Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-17 17:58 +0100
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 10:07 -0700
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 10:09 -0700
Re: sizeof(arr[0]) David Kleinecke <dkleinecke@gmail.com> - 2015-06-17 10:46 -0700
Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-17 11:13 -0700
Re: sizeof(arr[0]) Nathan Wagner <nw@hydaspes.if.org> - 2015-06-18 07:14 +0000
Re: sizeof(arr[0]) David Brown <david.brown@hesbynett.no> - 2015-06-18 09:54 +0200
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-18 05:19 -0700
Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-17 10:53 -0700
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 11:17 -0700
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 13:59 -0700
Re: sizeof(arr[0]) Ian Collins <ian-news@hotmail.com> - 2015-06-18 13:41 +1200
Re: sizeof(arr[0]) David Brown <david.brown@hesbynett.no> - 2015-06-18 10:04 +0200
Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 13:18 -0700
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 21:30 +0100
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 13:53 -0700
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 13:43 -0700
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 21:52 +0100
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 14:01 -0700
Re: sizeof(arr[0]) David Brown <david.brown@hesbynett.no> - 2015-06-16 23:49 +0200
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 14:58 -0700
Re: sizeof(arr[0]) David Brown <david.brown@hesbynett.no> - 2015-06-17 14:10 +0200
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-17 13:20 +0100
Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 14:16 -0700
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 14:39 -0700
Re: sizeof(arr[0]) gazelle@shell.xmission.com (Kenny McCormack) - 2015-06-16 18:38 +0000
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 11:45 -0700
Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 13:22 -0700
Re: sizeof(arr[0]) gazelle@shell.xmission.com (Kenny McCormack) - 2015-06-16 21:25 +0000
Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 11:05 -0700
Re: sizeof(arr[0]) James Kuyper <jameskuyper@verizon.net> - 2015-06-16 14:15 -0400
Re: sizeof(arr[0]) David Kleinecke <dkleinecke@gmail.com> - 2015-06-17 10:07 -0700
Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-17 11:16 -0700
Re: sizeof(arr[0]) David Kleinecke <dkleinecke@gmail.com> - 2015-06-18 10:22 -0700
Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-18 10:42 -0700
Re: sizeof(arr[0]) David Kleinecke <dkleinecke@gmail.com> - 2015-06-18 11:41 -0700
Re: sizeof(arr[0]) Philip Lantz <prl@canterey.us> - 2015-06-16 00:12 -0700
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 10:12 +0100
Re: sizeof(arr[0]) Philip Lantz <prl@canterey.us> - 2015-06-16 09:12 -0700
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 17:32 +0100
Re: sizeof(arr[0]) kuznecov.alexey@gmail.com - 2015-06-10 14:56 -0700
Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-10 23:53 +0100
Re: sizeof(arr[0]) Bartc <bc@freeuk.com> - 2015-06-11 00:33 +0100
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-11 00:37 +0100
Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 06:05 -0700
[OT] The number 42 (was Re: sizeof(arr[0])) David Brown <david.brown@hesbynett.no> - 2015-06-17 16:07 +0200
Re: [OT] The number 42 (was Re: sizeof(arr[0])) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 08:23 -0700
Re: [OT] The number 42 (was Re: sizeof(arr[0])) David Brown <david.brown@hesbynett.no> - 2015-06-18 10:21 +0200
Re: [OT] The number 42 (was Re: sizeof(arr[0])) David Kleinecke <dkleinecke@gmail.com> - 2015-06-17 10:35 -0700
Re: [OT] The number 42 (was Re: sizeof(arr[0])) David Brown <david.brown@hesbynett.no> - 2015-06-18 10:18 +0200
Re: [OT] The number 42 (was Re: sizeof(arr[0])) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-18 10:08 +0100
Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-17 15:13 +0100
Re: sizeof(arr[0]) raltbos@xs4all.nl (Richard Bos) - 2015-06-18 20:38 +0000
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