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Re: size_t in a struct

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Ben Pfaff <blp@cs.stanford.edu> writes:
> 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.

Or in order of alignment, which might not be the same thing.

On some architectures, there could be an advantage to putting
as many small members as possble at the beginning of the struct,
because smaller offsets can be faster.

If C didn't require that struct members to follow their declared
order, the compiler could optimize the layout any way that makes
sense.  It's too late to change that without breaking existing code,
but perhaps a future standard could add an attribute to specify
that the the compiler can alter the layout -- or it could be a
compiler-specific extension.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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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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