Re: STL map insert Options

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From	Ian Collins <ian-news@hotmail.com>
Newsgroups	comp.lang.c++
Subject	Re: STL map insert Options
Date	Thu, 14 Jul 2011 07:57:29 +1200
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On 07/14/11 02:31 AM, Stephen Howe wrote:

Please don't snip attributions, it's rude.

>> I'd be very surprised if all three didn't compile down to the same
>> assembly code.  It certainly does with the two compilers I tried.
>>
>> Ian Collins
>
> I have just rechecked with Visual Studio 2008, 8 years later and I get
> the same results.
> And that is with full optimisations switched on.
> It is easy to see why as make_pair()/pair() are creating an actual
> object to insert, value_type does not. So that is an extra round of
> copy constructors/destructors.
> You might be using ints and the compilers you use might optimise out
> extra assignments.
>
> With the code referenced in the link, I get (and it is not too hard to
> work out what work map actually does).

If you change the code to use the same type as the map::value_type, all 
things are equal.  For example:

     m.insert(pair<const Key, Value>(t2, tv));

<snip>

-- 
Ian Collins

Thread

STL map insert Options mrc2323@cox.net (Mike Copeland) - 2011-07-05 14:13 -0700
  Re: STL map insert Options Ian Collins <ian-news@hotmail.com> - 2011-07-06 10:28 +1200
  Re: STL map insert Options Paavo Helde <myfirstname@osa.pri.ee> - 2011-07-06 01:14 -0500
  Re: STL map insert Options Stephen Howe <stephen.howe@kantarmedia.com> - 2011-07-12 13:29 -0700
    Re: STL map insert Options Ian Collins <ian-news@hotmail.com> - 2011-07-13 09:01 +1200
      Re: STL map insert Options Stephen Howe <stephen.howe@kantarmedia.com> - 2011-07-13 07:31 -0700
        Re: STL map insert Options Leigh Johnston <leigh@i42.co.uk> - 2011-07-13 15:59 +0100
        Re: STL map insert Options Ian Collins <ian-news@hotmail.com> - 2011-07-14 07:57 +1200
          Re: STL map insert Options Pavel <pauldontspamtolk@removeyourself.dontspam.yahoo> - 2011-07-14 00:07 -0400
            Re: STL map insert Options Ian Collins <ian-news@hotmail.com> - 2011-07-14 16:50 +1200
  Re: STL map insert Options Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-07-19 15:20 +0000

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