Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!haven!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: qsorting & managing struct arrays, pointer arrays
Keywords: can qsort accept array of pointers to struct?
Message-ID: <11366@smoke.BRL.MIL>
Date: 20 Oct 89 21:58:46 GMT
References: <169@cica.cica.indiana.edu>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 13

In article <169@cica.cica.indiana.edu> burleigh@cica.cica.indiana.edu (Frank Burleigh) writes:
>   Can the standard qsort accept not the array of structures, but
>   the array of pointers to structure members?

qsort() doesn't know what the array it is sorting consists of;
it leaves that up to the comparison function.  Thus, a standard
trick is to have qsort() sort an array of pointers to records
rather than an array of records.  The rest is merely a matter
of getting the type declarations right; this amounts to adding
an extra * to the parameters in the comparison function.  Note
that the comparison function is fed "generic" pointers (void* or
char*), and you ought to cast them into record_type**s before
using them in the comparison function.