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Re: evaluate a generic swap function

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"Stanley Rice" <heconghui@gmail.com> wrote in message
news:fae63bac-e9c4-48e2-9c4f-e0269b2b3f2c@w8g2000yqi.googlegroups.com...

> I wrote a "generic" swap function, which can swap some type, such as
> int, double, long. But I don't know how to evaluate this function, and
> don't know whether it's a good idea to use such a function. I hope you
> can give me some suggestions.
>
> void swap(void *left, void *right, size_t siz)
> {
>    char *buf;
>
>    buf = (char *)malloc(sizeof(*buf) * siz);
>
>    memcpy(buf, left, siz);
>    memcpy(left, right, siz);
>    memcpy(right, buf, siz);
>
>    free(buf);
> }
>
> call this function in the following ways:
>    int a = 5;
>    int b = 4;
>    swap(&a, &b, sizeof(a));

What are the most common things to swap? If they are basic types such as
ints or chars, then your function will be inefficient, if you're planning to
do a lot of swapping. You also have to consider than malloc() calls are
costly, and subject to failure.

Since you will usually know what types of being swapped, it wouldn't be
difficult to add a few streamlined versions of swap(): swap_int(),
swap_double(), etc.

Or the size can be tested inside swap(), and values such as 4 or 8 can be
identified and deal with quickly without any allocations.

Also, if the size of the type is often going to be small, you might want to
just use a fixed-size buffer, such as:

 char buf_fixed[256];

and use that, without any memory management, if the size happens to be <=
256, otherwise you'd need malloc(). (VLAs which someone suggested using are 
also viable, if the size is not going to be so huge that you get stack 
overflows.)

-- 
Bartc 

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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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