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From: cpcahil@virtech.UUCP (Conor P. Cahill)
Newsgroups: comp.lang.c
Subject: Re: swap(x,y)
Message-ID: <1065@virtech.UUCP>
Date: 24 Aug 89 01:38:16 GMT
References: <MYwDEFy00WB842JEUx@andrew.cmu.edu> <1061@virtech.UUCP> <17504@ut-emx.UUCP>
Organization: Virtual Technologies Inc
Lines: 30

In article <17504@ut-emx.UUCP>, pmaniac@walt.cc.utexas.edu (Noah Friedman) writes:
> To prevent this problem, why not cast the arguments as doubles?
> 
> void swap(double *x, double *y) 
> {     *x += *y;    *y = *x - *y;   *x -= *y; }
> 
> func()
> {
>  int a, b;
>     swap((double *) &a, (double *) &b);
> }

This would not work, and would probably cause a core drop, because

	1. The swap will always modify sizeof(double) bytes.  a is 
	   sizeof(int) bytes and usually the two are not the same.  Casting
	   an address does NOT effect the data the address refers to.

	2. The data at &a will probably not meet the standard for 
	   representation as a double and would likely cause a floating
	   point exception.

	3. If the data items were doubles, you could still overflow in 
	   the first statement.

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