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From: tac@cs.brown.edu (Theodore A. Camus)
Newsgroups: comp.lang.c
Subject: Re: Swapping two variables in place
Message-ID: <50830@brunix.UUCP>
Date: 23 Sep 90 18:29:19 GMT
References: <26101@shamash.cdc.com> <26310@cs.yale.edu>
Sender: news@brunix.UUCP
Reply-To: tac@cs.brown.edu (Theodore A. Camus)
Organization: Brown University Department of Computer Science
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>There was a message a while back about not being able to create a good
>#define function to swap two variables.
>
>How about this one: #define swap(a,b) a^=b^=a^=b

>But it won't work on `float's and `double's, as `^' is defined only on
>integral types.


Nor would it work for swap(i,A[i]).  
In fact, the usual { tmp = i ;  i = A[i] ; A[i] = tmp }  
would fail too.  Thus the danger of call-by-name.  

[ref 2nd Dragon book]



  CSnet:     tac@cs.brown.edu                          Ted Camus  
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  "An ounce of example is worth a pound of theory."    Providence, RI 02912