Re: qsort() standard functions

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From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.c
Subject	Re: qsort() standard functions
Date	Thu, 25 Apr 2019 22:45:20 +0100
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Anton Shepelev <anton.txt@gmail.com> writes:

You play fast and loose with types here!  One case prevents compilation
and there is also an int overflow bug that really matters.

> #include <stdio.h>
> #include <stdlib.h>
> #include <time.h>
> #include "sort.h"
>
> void print( int * a, int n )
> {  int i;
>    for( i = 0; i < n; i++ )
>       printf("%i ", a[i] );
>    printf("\n");
> }
>
> /* comparison function: */
> int comp( void * data, int i, int j )
> {  return ( (int*)data )[i] -
>           ( (int*)data )[j];
> }

Your header specifies a fourth parameter:

  typedef int  (*comp_f)( void * data, int i, int j, const void * extra );

Also, did you mean for the "const"s to be the other way round?

  typedef int (*comp_f)(const void *data, int i, int j, void * extra);

makes more sense to me.  (I'd use size_t for all the offsets but not
doing that is presumably a deliberate decision on your part.)

> /* comparison function for standard qsort: */
> compar(const void * a, void * b)
> {  return *((int*)a) - *((int*)b);
> }

qsort wants both pointers to point to const void.  Also, this
declaration uses implicit int, but I think you said you write C90.  Mind
you, adding the return type is, to my mind, good practise even in C90.

> /* swap function: */
> void swap( void * data, int i, int j )
> {  int buf;
>    buf = ( (int[])data )[i];

You can't cast to an array type, nor to an incomplete type; int [] is both!

>    ( (int*)data )[i] = ( (int*)data )[j];
>    ( (int*)data )[j] = buf;
> }

Subtracting ints can lead to unintended behaviour when the result
overflows, even when the actual behaviour is the expected "wrap-around"
one.

I don't want to be overly negative -- you are one of the few people who
posts actual code here.  I really liked your sort function.

-- 
Ben.

Thread

qsort() standard functions rick.c.hodgin@gmail.com - 2019-04-24 09:08 -0700
  Re: qsort() standard functions gazelle@shell.xmission.com (Kenny McCormack) - 2019-04-24 16:12 +0000
    Re: qsort() standard functions rick.c.hodgin@gmail.com - 2019-04-24 09:18 -0700
      Re: qsort() standard functions Chad <cdalten@gmail.com> - 2019-05-02 12:02 -0700
    Re: qsort() standard functions Real Troll <real.troll@trolls.com> - 2019-04-24 22:30 -0400
      Re: qsort() standard functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 19:32 -0700
        Re: qsort() standard functions Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-04-25 10:19 +0000
          Re: qsort() standard functions rick.c.hodgin@gmail.com - 2019-04-25 04:09 -0700
            Re: qsort() standard functions Richard Damon <Richard@Damon-Family.org> - 2019-04-25 08:13 -0400
              Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-25 06:39 -0700
              Re: qsort() standard functions already5chosen@yahoo.com - 2019-04-25 07:23 -0700
      Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-25 00:39 -0700
        Re: qsort() standard functions Real Troll <Real.Troll@Trolls.com> - 2019-04-25 23:27 +0100
  Re: qsort() standard functions John Bode <jfbode1029@gmail.com> - 2019-04-24 09:34 -0700
    Re: qsort() standard functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 09:47 -0700
    Re: qsort() standard functions John Bode <jfbode1029@gmail.com> - 2019-04-24 09:47 -0700
      Re: qsort() standard functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 12:54 -0400
        Re: qsort() standard functions John Bode <jfbode1029@gmail.com> - 2019-04-24 11:33 -0700
          Re: qsort() standard functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 14:41 -0400
            Re: qsort() standard functions John Bode <jfbode1029@gmail.com> - 2019-04-24 11:52 -0700
              Re: qsort() standard functions gazelle@shell.xmission.com (Kenny McCormack) - 2019-04-24 19:12 +0000
              Re: qsort() standard functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 16:05 -0400
                Re: qsort() standard functions queequeg@trust.no1 (Queequeg) - 2019-04-24 20:39 +0000
            Re: qsort() standard functions James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-04-24 16:33 -0700
      Re: qsort() standard functions gazelle@shell.xmission.com (Kenny McCormack) - 2019-04-24 19:18 +0000
        Re: qsort() standard functions Bart <bc@freeuk.com> - 2019-04-24 20:28 +0100
          Re: qsort() standard functions gazelle@shell.xmission.com (Kenny McCormack) - 2019-04-24 21:27 +0000
        Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-24 12:31 -0700
        Re: qsort() standard functions John Bode <jfbode1029@gmail.com> - 2019-04-24 13:02 -0700
          Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-24 13:41 -0700
            Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-24 14:00 -0700
              Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-04-25 00:22 +0300
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-24 15:04 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-24 15:20 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-24 15:40 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-24 15:57 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-24 16:06 -0700
                Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-04-25 23:49 +0300
                Re: qsort() standard functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-04-25 22:45 +0100
                Re: qsort() standard functions Bart <bc@freeuk.com> - 2019-04-25 23:00 +0100
                Re: qsort() standard functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-04-25 23:24 +0100
                Re: qsort() standard functions Real Troll <Real.Troll@Trolls.com> - 2019-04-25 23:20 +0100
                Re: qsort() standard functions Anton Shepelev <anton.txt@g{oogle}mail.com> - 2019-04-26 13:06 +0300
                Re: qsort() standard functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-04-26 13:38 +0100
                Re: qsort() standard functions Anton Shepelev <anton.txt@g{oogle}mail.com> - 2019-04-26 16:43 +0300
                Re: qsort() standard functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-04-26 17:46 +0100
                Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-04-27 14:55 +0300
                Re: qsort() standard functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-04-27 14:59 +0100
                Re: qsort() standard functions Robert Wessel <robertwessel2@yahoo.com> - 2019-04-27 11:41 -0500
                Re: qsort() standard functions Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-05-02 09:46 -0700
                Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-05-02 20:35 +0300
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-05-02 15:35 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-05-05 04:39 -0700
                Re: qsort() standard functions Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-05-04 07:35 -0700
                Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-05-05 00:01 +0300
                Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-05-02 15:11 +0300
                Re: qsort() standard functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-05-02 16:36 +0100
                Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-04-27 14:47 +0300
                Re: qsort() standard functions Robert Wessel <robertwessel2@yahoo.com> - 2019-04-27 08:30 -0500
                Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-05-02 14:52 +0300
                Re: qsort() standard functions Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-05-04 07:13 -0700
                Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-05-05 22:57 +0300
                Re: qsort() standard functions David Brown <david.brown@hesbynett.no> - 2019-05-06 10:09 +0200
                Re: qsort() standard functions Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-06-01 05:22 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-25 17:09 -0700
                Re: qsort() standard functions Bart <bc@freeuk.com> - 2019-04-26 10:58 +0100
                Re: qsort() standard functions mark.bluemel@gmail.com - 2019-04-26 03:59 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-26 06:34 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-26 07:16 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-26 07:45 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-26 08:29 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-26 12:06 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-26 13:09 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-26 13:37 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-26 14:05 -0700
                Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-04-27 14:59 +0300
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-27 06:19 -0700
                Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-27 06:32 -0700
  Re: qsort() standard functions Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-04-24 10:54 -0600
    Re: qsort() standard functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 10:10 -0700
    Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-04-25 00:06 +0300
  Re: qsort() standard functions scott@slp53.sl.home (Scott Lurndal) - 2019-04-24 17:37 +0000
    Re: qsort() standard functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 10:56 -0700
      Re: qsort() standard functions Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-04-24 12:12 -0600
        Re: qsort() standard functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 14:27 -0400
          Re: qsort() standard functions John Bode <jfbode1029@gmail.com> - 2019-04-24 11:44 -0700
            Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-24 11:57 -0700
              Re: qsort() standard functions fir <profesor.fir@gmail.com> - 2019-04-24 12:04 -0700
            Re: qsort() standard functions nobody@example.org (Scott) - 2019-04-25 01:16 +0000
              Re: qsort() standard functions James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-04-24 21:38 -0400
  Re: qsort() standard functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 14:42 -0400
    Re: qsort() standard functions David Brown <david.brown@hesbynett.no> - 2019-04-24 22:13 +0200
    Re: qsort() standard functions queequeg@trust.no1 (Queequeg) - 2019-04-24 20:46 +0000
  Re: qsort() standard functions jadill33@gmail.com - 2019-04-24 14:01 -0700
  Re: qsort() standard functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2019-04-24 15:41 -0700
  Re: qsort() standard functions "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2019-04-26 22:24 +0800
    Re: qsort() standard functions Anton Shepelev <anton.txt@gmail.com> - 2019-05-02 15:05 +0300
      Re: qsort() standard functions "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2019-05-03 17:02 +0800
        Re: qsort() standard functions Chad <cdalten@gmail.com> - 2019-05-03 10:10 -0700
          Re: qsort() standard functions "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2019-05-04 01:22 +0800
            Re: qsort() standard functions Chad <cdalten@gmail.com> - 2019-05-03 15:14 -0700
              [OT]Eternal.... programmer? "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2019-05-04 06:20 +0800
                Re: [OT]Eternal.... programmer? Chad <cdalten@gmail.com> - 2019-05-04 05:53 -0700

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