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From: sean@ms.uky.edu (Sean Casey)
Newsgroups: comp.unix.wizards
Subject: Why doesn't this qsort example work?
Message-ID: <7527@g.ms.uky.edu>
Date: Mon, 19-Oct-87 03:21:45 EDT
Article-I.D.: g.7527
Posted: Mon Oct 19 03:21:45 1987
Date-Received: Tue, 20-Oct-87 01:05:55 EDT
Organization: The Leaning Tower of Patterson Office @ The Univ. of KY
Lines: 41
Keywords: argh, frustration, core dump


I'm trying to use qsort(3) for the first time and I'm having a bit of
trouble.  I've included some code here that reproduces the problem.
The following C program coredumps because compar() is being called with
bogus arguments.  I'm sure it's my fault, but I just can't seem to see
what I'm doing wrong.  Maybe one of you can tell me:

struct tstr {
	int a;
	int b;
};

compar(x, y)
struct tstr *x, *y;
{
	if (x->a < y->a)	/* coredumps here, therefore a or b is bogus */
		return(-1);	/* a < b */
	if (x->a > y->a)
		return(1);	/* a > b */
	return(0);		/* a = b */
}

main()
{
	struct tstr t[2];

	t[0].a = 1;
	t[1].a = 2;
	/* this sorts t[] by the "a" field */
	qsort(&t[0], 2, sizeof(struct tstr), (*compar)());
}


Thanks for any light you can shed,

Sean

-- 
--  Sean Casey               sean@ms.uky.edu, {rutgers,uunet,cbosgd}!ukma!sean
--  (the Empire guy)         sean@ms.uky.csnet,  sean@UKMA.BITNET
--  "Have fun storming the castle!" - Miracle Max