Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!purdue!mentor.cc.purdue.edu!aic
From: aic@mentor.cc.purdue.edu (George A. Basar)
Newsgroups: comp.lang.c
Subject: Re: Help with qsort
Message-ID: <5314@mentor.cc.purdue.edu>
Date: 20 Nov 89 22:09:04 GMT
References: <1989Nov20.213702.20821@agate.berkeley.edu>
Distribution: usa
Organization: Buckaroo Banzai Institute
Lines: 27

In article <1989Nov20.213702.20821@agate.berkeley.edu>, ilan343@violet.berkeley.edu writes:
> I am trying to use the standard C qsort routine to rank an array of
> floats.  I don't want to disturb the original data, so I tried the
> following:
> 
> a) Copy the addresses of each array element into an array of pointers.
> b) Invoke qsort on the array of pointers. 
> c) Print ranks by subtracting pointers

  No need for step c, the entries in rank are pointers which had been sorted
  based upon the values in data.

> 	printf ("%d %f %d \n", i, data[i], rank[i] - data);

  This should be
 	printf ("%d %f %f \n", i, data[i], *rank[i]);

  Since your compare checks the value in data, qsort swapped pointers in 
rank.  Printing out the values referenced by the elements in rank in
order, as above, gives a sorted list.


* George A. Basar                              (317)742-8799 (home)
* aic@mentor.cc.purdue.edu                     BASAR@PURCCVM.BITNET    
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