Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ?

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ?
Date	2013-01-13 16:57 -0800
Organization	None to speak of
Message-ID	<ln7gngd1jz.fsf@nuthaus.mib.org> (permalink)
References	(10 earlier) <kcsq2q$8je$1@dont-email.me> <lnk3rihu51.fsf@nuthaus.mib.org> <kcv9cb$a2g$1@dont-email.me> <lnfw24d55f.fsf@nuthaus.mib.org> <kcviqf$344$1@dont-email.me>

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Shao Miller <sha0.miller@gmail.com> writes:
> On 1/13/2013 18:39, Keith Thompson wrote:
[...]
>> So you'd rather iterate over every element of the array, and then
>> test i%10 to decide whether to process the current one?
>>
>>      for (i = 0; i < sizeof arr / sizeof arr[0]; i ++) {
>>          if (i % 10 == 0) {
>>              /* ... */
>>          }
>>      }
>>
>> I find that more verbose, less clear, and almost certainly less
>> efficient (unless the compiler is clever enough to transform it
>> into the first form).  All to solve a problem that is not a problem
>> at all.
>>
>> If there's some concern about i overflowing the upper limit of its
>> type (INT_MAX or SIZE_MAX), I'd probably precompute the last index
>> I want to look at and use that to control the loop.  But I see no
>> point in doing so just to avoid letting i exceed the upper bound
>> of the array, when the code explicitly avoids accessing anything
>> outside the array bounds.
>
> No, I was talking about if the loop was for initialization.  In such a 
> case, I'd initialize every element (advancing by 1), but if something 
> special was needed for every tenth, I could determine that with your 'if'.

Who says the loop is for initialization?  It might not even be writing
to the array.

> For just _working_ with an already-initialized array, I'd probably use 
> precisely this loop (though I might possibly be more inclined to put it 
> in a function and pass the count).  BUT, as was snipped, if the count of 
> 'arr' is 4, then the programmer _really_ ought to have their head 
> checked. :)

Absurd.

A function that, for whatever reason, needs to access every 10th
(or every Nth) element, can perfectly sensibly work on an array of
any size.  If the array has 10 or fewer elements, the function just
accesses element 0.  I see no reason to treat that as a special case.

-- 
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"

Thread

[MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? m.labanowicz@gmail.com - 2013-01-09 07:26 -0800
  Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? James Kuyper <jameskuyper@verizon.net> - 2013-01-09 11:30 -0500
  Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-01-09 11:58 -0500
    Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Robert Wessel <robertwessel2@yahoo.com> - 2013-01-09 12:27 -0600
    Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-09 11:22 -0800
  Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-09 14:39 -0500
  Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? m.labanowicz@gmail.com - 2013-01-10 02:40 -0800
    Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-10 08:31 -0500
      Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-10 08:49 -0500
        Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? m.labanowicz@gmail.com - 2013-01-10 06:48 -0800
          Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-10 10:33 -0500
      Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-11 08:19 -0800
        Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-11 12:46 -0500
          Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-11 14:04 -0800
            Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-01-11 22:42 +0000
              Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-12 01:44 +0000
            Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-11 19:30 -0500
              Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-11 20:11 -0500
              Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-01-12 01:17 +0000
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-11 20:46 -0500
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-01-12 03:14 +0000
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-12 14:17 -0800
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-12 18:02 -0500
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-12 15:13 -0800
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-13 16:36 -0500
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-13 15:39 -0800
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-13 19:17 -0500
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-13 16:57 -0800
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-13 20:50 -0500
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-13 19:08 -0800
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-14 00:00 -0500
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-01-14 21:21 +0000
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-14 17:50 -0500
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-01-14 01:23 +0000
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-13 21:04 -0500
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-13 19:13 -0800
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-01-14 21:37 +0000
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-11 18:28 -0800
              Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Keith Thompson <kst-u@mib.org> - 2013-01-11 18:40 -0800
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-12 04:30 -0500
    Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-10 14:37 +0000
      Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? m.labanowicz@gmail.com - 2013-01-10 06:51 -0800
        Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? m.labanowicz@gmail.com - 2013-01-10 07:41 -0800
          Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-10 16:55 +0000
          Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? Shao Miller <sha0.miller@gmail.com> - 2013-01-10 17:41 -0500
            Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? m.labanowicz@gmail.com - 2013-01-11 03:03 -0800
              Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? m.labanowicz@gmail.com - 2013-01-11 04:14 -0800
                Re: [MUDFLAP] Is sizeof(ARRAY[0]) equivalent to sizeof(*ARRAY) ? James Kuyper <jameskuyper@verizon.net> - 2013-01-11 08:32 -0500

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