NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/8324

Internet Message Format | 1996-08-05 | 1.7 KB

Path: news.clark.net!usenet
From: [e-mail] (yom)
Newsgroups: comp.lang.c
Subject: Re: more problems with qsort
Date: 3 Mar 1996 05:19:51 GMT
Organization: home
Message-ID: <4hba5n$[e-mail]>
References: <[e-mail]> <4h0j9e$[e-mail]> <4h81m0$[e-mail]>
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In article <4h81m0$[e-mail]>, [e-mail]
says...
>
>In article <4h0j9e$[e-mail]>, yom <[e-mail]> wrote:
>>Since you're trying to sort a char**, the qsort function call must
>>look like this:
>
>>qsort(array,lines,sizeof(char **),(int (*)(void *,void *)) compare);
>
>This is entirely wrong.  If you're trying to sort an array of pointers
>to char (or a char ** acting like an array of char *'s), you must use
>        qsort(ary, nelem, sizeof(array[0]), compare);
>... and array[0] will be a char *, which may be different from a
>char **.

Oops.  You're correct.  Thanks for correcting the mistake.

>
>>And your compare function must be defined like this:
>
>>int compare(char **a,char **b) {return strcmp(*a,*b);}
>
>No, it really mustn't.  It must be defined like this:
>int compare(const void *a, const void *b) {
>        return strcmp(*(char **) a, *(char **) b);
>}

Well I disagree on this one. Results of 1) defining the compare
function that takes two char** arguments and casting the function call
to qsort and 2) defining the compare function that takes two void*
arguments and casting the arguments to char ** in strcmp call are
identical.  Also, I tend to not use "const" because some compilers do
not support it.

Song ([e-mail])