Re: How to use a struct with qsort()?

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: How to use a struct with qsort()?
Date	2019-10-26 16:08 -0700
Organization	None to speak of
Message-ID	<lnmudn9kay.fsf@kst-u.example.com> (permalink)
References	(4 earlier) <BkKqF.69070$1A2.65981@fx07.iad> <qovf0n$1lfh$1@gioia.aioe.org> <kUUsF.1229971$WI2.370840@fx34.am4> <qp1mtt$1f9h$1@gioia.aioe.org> <vC3tF.55417$SW2.31092@fx24.iad>

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DFS <nospam@dfs.com> writes:
[...]
> So I try it in my code, to replace a small loop:
>
> int wsvals[26]={0};   (not a char as in previous examples)
> memset(wsvals,0,26);
>
> Doesn't work.  The code compiles (tcc Windows) with no warnings, but it 
> doesn't execute.

I presume it does execute.  It just doesn't do what you wanted it to do.

> Finally on stackoverflow I find this:
> "Note that for memset you have to pass the number of bytes, not the 
> number of elements because this is an old C function:
>
> So I do:  memset(wsvals,0,26 * sizeof(int));
>
> And it works.
>
> Most of the descriptions on the web say memset "is used to fill a block 
> of memory with given/particular value."  No mention of the datatype.
>
> Why do I need to also use sizeof() for an int but not a char?

Because sizeof (char) is 1 by definition.  Given:
    char arr[26];
you could do either
    memset(arr, 0, 26);
or
    memset(arr, 0, 26*sizeof(char));
Both are equivalent.

But given an array of any type that you want to zero-fill, just apply
sizeof to the entire object:
    int wsvals[26];
    memset(wsvals, 0, sizeof wsvals);

Note also that in your example, you already initialized the array:
    int wsvals[26]={0};
so there's no need to call memset.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */

Thread

How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-19 13:35 -0400
  Re: How to use a struct with qsort()? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-10-19 10:22 -0700
    Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-19 14:19 -0400
      Re: How to use a struct with qsort()? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-19 19:36 +0100
      Re: How to use a struct with qsort()? Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-19 18:44 +0000
  Re: How to use a struct with qsort()? Barry Schwarz <schwarzb@delq.com> - 2019-10-19 10:23 -0700
  Re: How to use a struct with qsort()? Ike Naar <ike@sdf.lonestar.org> - 2019-10-19 19:09 +0000
    Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-19 15:51 -0400
      Re: How to use a struct with qsort()? already5chosen@yahoo.com - 2019-10-19 13:09 -0700
        Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-19 16:26 -0400
          Re: How to use a struct with qsort()? already5chosen@yahoo.com - 2019-10-19 13:51 -0700
            Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-19 17:24 -0400
              Re: How to use a struct with qsort()? already5chosen@yahoo.com - 2019-10-19 14:49 -0700
                Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-19 18:26 -0400
                Re: How to use a struct with qsort()? already5chosen@yahoo.com - 2019-10-19 16:32 -0700
                Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-20 09:22 -0400
                Re: How to use a struct with qsort()? Paul <nospam@needed.invalid> - 2019-10-26 04:15 -0400
                Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-26 09:37 -0400
                Re: How to use a struct with qsort()? Bart <bc@freeuk.com> - 2019-10-26 15:40 +0100
                Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-28 19:49 -0400
                Re: How to use a struct with qsort()? Paul <nospam@needed.invalid> - 2019-10-29 01:59 -0400
                Re: How to use a struct with qsort()? Paul <nospam@needed.invalid> - 2019-10-30 04:54 -0400
                Re: How to use a struct with qsort()? Bart <bc@freeuk.com> - 2019-10-30 11:54 +0000
                Re: How to use a struct with qsort()? Keith Thompson <kst-u@mib.org> - 2019-10-30 08:58 -0700
                Re: How to use a struct with qsort()? Öö Tiib <ootiib@hot.ee> - 2019-11-07 01:10 -0800
                Re: How to use a struct with qsort()? Bart <bc@freeuk.com> - 2019-11-07 10:51 +0000
                Re: How to use a struct with qsort()? Paul <nospam@needed.invalid> - 2019-10-26 15:03 -0400
                Re: How to use a struct with qsort()? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-26 21:50 +0100
                Re: How to use a struct with qsort()? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-04 16:02 -0800
            Re: How to use a struct with qsort()? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-10-21 11:58 +0000
            Re: How to use a struct with qsort()? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-10-23 04:51 -0700
          Re: How to use a struct with qsort()? Bart <bc@freeuk.com> - 2019-10-19 23:25 +0100
            Re: How to use a struct with qsort()? Keith Thompson <kst-u@mib.org> - 2019-10-19 15:38 -0700
              Re: How to use a struct with qsort()? David Brown <david.brown@hesbynett.no> - 2019-10-20 14:44 +0200
              Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-22 15:42 -0400
              Re: How to use a struct with qsort()? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-10-23 05:47 -0700
                Re: How to use a struct with qsort()? Bart <bc@freeuk.com> - 2019-10-23 16:40 +0100
                Re: How to use a struct with qsort()? Keith Thompson <kst-u@mib.org> - 2019-10-23 13:51 -0700
                Re: How to use a struct with qsort()? Bart <bc@freeuk.com> - 2019-10-23 23:07 +0100
                Re: How to use a struct with qsort()? Keith Thompson <kst-u@mib.org> - 2019-10-23 15:50 -0700
                Re: How to use a struct with qsort()? Bart <bc@freeuk.com> - 2019-10-24 01:20 +0100
                Re: How to use a struct with qsort()? Keith Thompson <kst-u@mib.org> - 2019-10-23 18:20 -0700
                Re: How to use a struct with qsort()? Bart <bc@freeuk.com> - 2019-10-24 10:40 +0100
                Re: How to use a struct with qsort()? Keith Thompson <kst-u@mib.org> - 2019-10-24 11:00 -0700
          Re: How to use a struct with qsort()? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-20 00:30 +0100
            Re: How to use a struct with qsort()? Bart <bc@freeuk.com> - 2019-10-20 00:44 +0100
          Re: How to use a struct with qsort()? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-20 01:27 +0100
          Re: How to use a struct with qsort()? Manfred <noname@add.invalid> - 2019-10-25 20:30 +0200
            Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-25 16:07 -0400
            Re: How to use a struct with qsort()? Ike Naar <ike@sdf.lonestar.org> - 2019-10-26 07:27 +0000
              Re: How to use a struct with qsort()? Keith Thompson <kst-u@mib.org> - 2019-10-26 02:11 -0700
            Re: How to use a struct with qsort()? Bart <bc@freeuk.com> - 2019-10-26 11:06 +0100
              Re: How to use a struct with qsort()? Manfred <noname@invalid.add> - 2019-10-26 16:58 +0200
                Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-26 18:17 -0400
                Re: How to use a struct with qsort()? Keith Thompson <kst-u@mib.org> - 2019-10-26 16:08 -0700
                Re: How to use a struct with qsort()? DFS <nospam@dfs.com> - 2019-10-26 21:33 -0400
                Re: How to use a struct with qsort()? Keith Thompson <kst-u@mib.org> - 2019-10-26 22:10 -0700
                Re: How to use a struct with qsort()? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-10-27 01:48 +0100
                Re: How to use a struct with qsort()? Manfred <noname@invalid.add> - 2019-10-27 19:29 +0100
                Re: How to use a struct with qsort()? Barry Schwarz <schwarzb4aarp@gmail.com> - 2019-10-27 13:09 -0700

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