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Groups > comp.lang.c > #4544

Re: size_t in a struct

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On 5/22/2011 12:37 PM, Ben Pfaff wrote:
> Shao Miller<sha0.miller@gmail.com>  writes:
>
>> On 5/22/2011 4:08 AM, Dr Nick wrote:
>> I guess a code generator could potentially accomplish something close
>> to this.  I'd be interested in an algorithm which figures out the most
>> size-efficient ordering of the members, if anyone has one (or some
>> ideas for one).
>
> Just sort the members into descending order of size.

I might be missing something...  Suppose an 'int' has both size and 
alignment of 4:

   sizeof (struct {
       char ca1[5];  /* 0 through 4 */
       /* 3 bytes of padding; 5 through 7 */
       int i;        /* 8 through 11 */
       /* No padding */
       char ca2[3];  /* 12 through 14 */
       /* 1 byte of padding; 15 */
     }) == 16

The above is most likely, right?  Whereas:

   sizeof (struct {
       int i;        /* 0 through 3 */
       /* No padding */
       char ca1[5];  /* 4 through 8 */
       /* No padding */
       char ca2[3];  /* 9 through 11 */
       /* No padding */
     }) == 12

Right?

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size_t in a struct Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2011-05-20 18:22 +0000
  Re: size_t in a struct Shao Miller <sha0.miller@gmail.com> - 2011-05-20 14:52 -0400
    Re: size_t in a struct Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2011-05-20 21:31 +0000
      Re: size_t in a struct Ian Collins <ian-news@hotmail.com> - 2011-05-21 09:51 +1200
        Re: size_t in a struct Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-05-24 21:34 +0300
          Re: size_t in a struct Ian Collins <ian-news@hotmail.com> - 2011-05-25 07:54 +1200
      Re: size_t in a struct "[the China Blue] Drill Baby Drill" <chine.bleu@yahoo.com> - 2011-05-20 15:06 -0700
        Re: size_t in a struct Angel <angel+news@spamcop.net> - 2011-05-20 22:51 +0000
      Re: size_t in a struct Keith Thompson <kst-u@mib.org> - 2011-05-20 15:39 -0700
        Re: size_t in a struct Edward Rutherford <edward.p.rutherford79@REMOVETHIS.gmail.com> - 2011-05-21 18:00 +0000
          Re: size_t in a struct Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-05-21 14:12 -0600
          Re: size_t in a struct Keith Thompson <kst-u@mib.org> - 2011-05-21 16:31 -0700
            Re: size_t in a struct Dr Nick <3-nospam@temporary-address.org.uk> - 2011-05-22 10:08 +0100
              Re: size_t in a struct Shao Miller <sha0.miller@gmail.com> - 2011-05-22 13:24 -0500
                Re: size_t in a struct Ben Pfaff <blp@cs.stanford.edu> - 2011-05-22 10:37 -0700
                Re: size_t in a struct Uncle Steve <stevet810@gmail.com> - 2011-05-22 14:18 -0400
                Re: size_t in a struct Keith Thompson <kst-u@mib.org> - 2011-05-22 12:17 -0700
                Re: size_t in a struct David Thompson <dave.thompson2@verizon.net> - 2011-06-01 16:33 -0400
                Re: size_t in a struct Shao Miller <sha0.miller@gmail.com> - 2011-05-23 02:05 -0500
                Re: size_t in a struct Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-05-23 11:21 +0100
                Re: size_t in a struct Shao Miller <sha0.miller@gmail.com> - 2011-05-23 19:40 -0500
                Re: size_t in a struct Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-05-24 01:25 +0100
                Re: size_t in a struct Shao Miller <sha0.miller@gmail.com> - 2011-05-23 20:43 -0500
          Re: size_t in a struct gordonb.d6jvy@burditt.org (Gordon Burditt) - 2011-05-22 17:48 -0500
      Re: size_t in a struct Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-05-21 15:43 +0000
  Re: size_t in a struct Keith Thompson <kst-u@mib.org> - 2011-05-20 11:59 -0700
  Re: size_t in a struct Nobody <nobody@nowhere.com> - 2011-05-20 22:24 +0100

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