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Re: evaluate a generic swap function

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jacob navia <jacob@spamsink.net> wrote:
> Le 20/09/11 15:51, Stanley Rice a écrit :
> in standard C:

> void swap(void *left, void *right, size_t siz)
> {
>       char buf[siz];

>       memcpy(buf, left, siz);
>       memcpy(left, right, siz);
>       memcpy(right, buf, siz);
> }

One word of caution: this is standard C according to the 1999
standard, variable length arrays weren't part of the 1989 C
standard. If you want to cater also for C89 compiler, i.e.
use your original code, I would drop the cast from this line

> buf = (char *)malloc(sizeof(*buf) * siz);

  buf = malloc( sizeof *buf * siz );

will do nicely unless you forgot to include <stdlib.h>.
(Note also that you don't need the parentheses around
'*buf' after 'sizeof', they are only needed if you take
the size of a type.)

You also might consider testing if malloc() suceeded by
checking that 'buf' has't been set to NULL. Of course,
the question then is on how to proceed. The way it's
written now the program would crash the program. You
could instead give the function a return value and re-
turn something indicating an error. Or you could use a
slower method for the swapping where you copy only smal-
ler parts of the data with a fixed size buffer in a loop.
Depends on how "bullet-proof" you need this function to
be.
                           Regards Jens
-- 
  \   Jens Thoms Toerring  ___      jt@toerring.de
   \__________________________      http://toerring.de

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evaluate a generic swap function Stanley Rice <heconghui@gmail.com> - 2011-09-20 06:51 -0700
  Re: evaluate a generic swap function jacob navia <jacob@spamsink.net> - 2011-09-20 16:01 +0200
    Re: evaluate a generic swap function jt@toerring.de (Jens Thoms Toerring) - 2011-09-20 14:29 +0000
      Re: evaluate a generic swap function jacob navia <jacob@spamsink.net> - 2011-09-20 21:13 +0200
        Re: evaluate a generic swap function jt@toerring.de (Jens Thoms Toerring) - 2011-09-20 20:30 +0000
          Re: evaluate a generic swap function Keith Thompson <kst-u@mib.org> - 2011-09-20 17:05 -0700
            Re: evaluate a generic swap function gazelle@shell.xmission.com (Kenny McCormack) - 2011-09-21 15:45 +0000
              Re: evaluate a generic swap function Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-09-21 09:33 -0700
              Re: evaluate a generic swap function jacob navia <jacob@spamsink.net> - 2011-09-21 19:17 +0200
                Re: evaluate a generic swap function gazelle@shell.xmission.com (Kenny McCormack) - 2011-09-21 17:34 +0000
                Re: evaluate a generic swap function Jack Foot <foot@dev.null.invalid> - 2011-09-21 18:12 +0000
  Re: evaluate a generic swap function Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-09-20 07:33 -0700
    Re: evaluate a generic swap function ImpalerCore <jadill33@gmail.com> - 2011-09-20 08:26 -0700
      Re: evaluate a generic swap function pete <pfiland@mindspring.com> - 2011-09-20 23:10 -0400
  Re: evaluate a generic swap function "BartC" <bc@freeuk.com> - 2011-09-20 22:20 +0100
    Re: evaluate a generic swap function jacob navia <jacob@spamsink.net> - 2011-09-20 23:23 +0200
      Re: evaluate a generic swap function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-09-20 23:07 +0100
  Re: evaluate a generic swap function Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-09-20 21:15 -0400
    Re: evaluate a generic swap function Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-09-21 03:17 -0700
  Re: evaluate a generic swap function Gene <gene.ressler@gmail.com> - 2011-09-21 02:40 -0700
  Re: evaluate a generic swap function Seebs <usenet-nospam@seebs.net> - 2011-09-23 01:46 +0000
    Re: evaluate a generic swap function Nelu <tandauioan@gmail.com> - 2011-09-23 10:26 -0700
      Re: evaluate a generic swap function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-09-23 18:36 +0100
        Re: evaluate a generic swap function Nelu <tandauioan@gmail.com> - 2011-09-23 10:49 -0700
          Re: evaluate a generic swap function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-09-23 20:18 +0100
            Re: evaluate a generic swap function Nelu <tandauioan@gmail.com> - 2011-09-23 12:54 -0700
              Re: evaluate a generic swap function James Kuyper <jameskuyper@verizon.net> - 2011-09-23 16:43 -0400
                Re: evaluate a generic swap function Nelu <tandauioan@gmail.com> - 2011-09-23 13:49 -0700
                Re: evaluate a generic swap function James Kuyper <jameskuyper@verizon.net> - 2011-09-23 17:44 -0400
                Re: evaluate a generic swap function Nelu <tandauioan@gmail.com> - 2011-09-23 18:04 -0700
                Re: evaluate a generic swap function Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-24 13:52 -0800
              Re: evaluate a generic swap function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-09-23 21:46 +0100
                Re: evaluate a generic swap function Nelu <tandauioan@gmail.com> - 2011-09-23 13:59 -0700
                Re: evaluate a generic swap function Seebs <usenet-nospam@seebs.net> - 2011-09-26 22:59 +0000
          Re: evaluate a generic swap function pete <pfiland@mindspring.com> - 2011-09-23 18:19 -0400
            Re: evaluate a generic swap function Nelu <tandauioan@gmail.com> - 2011-09-23 16:36 -0700

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