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Re: How to apply qsort() with a parameter?

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On 10/23/2012 10:05 AM, tom st denis wrote:
> On Oct 22, 4:54 pm, Eric Sosman <esos...@comcast-dot-net.invalid>
> wrote:
>> On 10/22/2012 4:25 PM, tom st denis wrote:
>>
>>> On Oct 22, 2:59 pm, Eric Sosman <esos...@comcast-dot-net.invalid>
>>> wrote:
>>>> [...]
>>>>        This setup repeats the switch decision -- which is "just
>>>> overhead" -- for every comparison, and there may be a lot of
>>>> them.  It would almost surely be better to have three short
>>>> comparators than one omnibus comparator.
>>
>>> But that code is not thread safe and it's not really any simpler than
>>> just calling qsort with a variable as the compare callback that is
>>> determined locally on the stack.
>>
>>       Since qsort() itself need not be thread-safe (it need not
>> even be re-entrant within just one thread), the thread-safety
>> of a comparator scarcely matters.  A thread-safe comparator
>> could be called by qsort() in one thread while another called
>> it via bsearch(), but that's a bit of a stretch.
>
> It's generally a bad idea to write thread unsafe code on purpose
> unless you have a reason.
>
>>       My personal parser recognizes all the words in your second
>> and third lines, but is unable to make sense of them.
>
> I was saying in the function where you call qsort() you could resolve
> there which key to sort on and then call the appropriate comparator
> function.  Instead of having one compare function you'd have n and
> they'd all compare a different key.

     Ah!  Okay, we're in violent agreement.  That's exactly
what I meant by suggesting "It would almost surely be better
to have three short comparators than one omnibus comparator."

-- 
Eric Sosman
esosman@comcast-dot-net.invalid

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Thread

How to apply qsort() with a parameter? rouben@shadow.(none) (Rouben Rostamian) - 2012-10-22 17:51 +0000
  Re: How to apply qsort() with a parameter? ImpalerCore <jadill33@gmail.com> - 2012-10-22 11:18 -0700
    Re: How to apply qsort() with a parameter? ImpalerCore <jadill33@gmail.com> - 2012-10-22 11:26 -0700
    Re: How to apply qsort() with a parameter? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-10-22 20:27 +0100
  Re: How to apply qsort() with a parameter? tom st denis <tom@iahu.ca> - 2012-10-22 11:38 -0700
  Re: How to apply qsort() with a parameter? Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-22 14:41 -0400
    Re: How to apply qsort() with a parameter? Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-22 14:59 -0400
      Re: How to apply qsort() with a parameter? tom st denis <tom@iahu.ca> - 2012-10-22 13:25 -0700
        Re: How to apply qsort() with a parameter? Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-22 16:54 -0400
          Re: How to apply qsort() with a parameter? Robert Wessel <robertwessel2@yahoo.com> - 2012-10-22 23:25 -0500
            Re: How to apply qsort() with a parameter? James Kuyper <jameskuyper@verizon.net> - 2012-10-23 07:42 -0400
            Re: How to apply qsort() with a parameter? Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-23 08:14 -0400
          Re: How to apply qsort() with a parameter? tom st denis <tom@iahu.ca> - 2012-10-23 07:05 -0700
            Re: How to apply qsort() with a parameter? Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-23 10:13 -0400
    Re: How to apply qsort() with a parameter? "Scott Fluhrer" <sfluhrer@ix.netcom.com> - 2012-10-23 10:28 -0400
      Re: How to apply qsort() with a parameter? Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-23 10:56 -0400
  Re: How to apply qsort() with a parameter? Öö Tiib <ootiib@hot.ee> - 2012-10-22 15:30 -0700
  Re: How to apply qsort() with a parameter? rouben@shady.(none) (Rouben Rostamian) - 2012-10-23 03:52 +0000
    Re: How to apply qsort() with a parameter? Keith Thompson <kst-u@mib.org> - 2012-10-22 22:46 -0700
      Re: How to apply qsort() with a parameter? pete <pfiland@mindspring.com> - 2012-10-23 16:03 -0400
    Re: How to apply qsort() with a parameter? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-10-23 06:43 -0700

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