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From: jc@atcmp.nl (Jan Christiaan van Winkel)
Newsgroups: comp.lang.c
Subject: Re: Brain Teaser
Message-ID: <578@atcmpe.atcmp.nl>
Date: 28 Mar 90 07:58:22 GMT
References: <10289@wpi.wpi.edu>
Organization: AT Computing, Nijmegen, The Netherlands
Lines: 27

From article <10289@wpi.wpi.edu>, by oesterle@wpi.wpi.edu (Shawn H. Oesterle):
! Problem:
! 	Swap two pointers without using a third pointer.
! Example:
! 	{
! 		void * x, * y, * tmp;
! 		tmp = x;
! 		x = y;
! 		y = x;
! 	}
! 
! 	Make a piece of code which has the same effect as this, but without
! 	using the 'tmp' variable (in C, of course).
The problem is that pointers cannot be used in arithmatic operations 
without the danger for inportability. Supposing x and y are ints (or longs),
you can do the following:
x=x^y; y=x^y; x=x^y;    /* swap x and y */

casting the pointers x and y to a long and v.v. is your responsability...
JC


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Jan Christiaan van Winkel         Tel: +31 80 566880              jc@atcmp.nl
AT Computing       P.O. Box 1428       6501 BK Nijmegen       The Netherlands
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