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Re: sizeof(arr[0])

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From Andrew Cooper <amc96@cam.ac.uk>
Newsgroups comp.lang.c
Subject Re: sizeof(arr[0])
Date Thu, 11 Jun 2015 00:27:28 +0100
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On 10/06/2015 22:08, Richard Heathfield wrote:
> I would draw the OP's attention to the omission of parentheses from the
> operand of sizeof:
> 
> ptr = malloc(n * sizeof *ptr);
> 
> There is no more need to write sizeof(*ptr) than there is to write +(x).
> 

While true, it quickly gets deceptive for more complicated expressions
such as 'sizeof(*p)->foo', where sizeof evaluates to the size of foo,
rather than the size of the object pointed to by p.

You owe it to anyone who reads your code, not to add to the cognitive
load of attempting to interpret it.

~Andrew

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Thread

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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