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From: gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>)
Newsgroups: net.lang.c
Subject: Re: How to pass subarrays?
Message-ID: <10378@brl-tgr.ARPA>
Date: Thu, 2-May-85 17:03:24 EDT
Article-I.D.: brl-tgr.10378
Posted: Thu May  2 17:03:24 1985
Date-Received: Sat, 4-May-85 00:47:52 EDT
References: <2839@ncsu.UUCP>
Organization: Ballistic Research Lab
Lines: 31

> #define S 20
> main()
> {
> 	int	big[S][S],
> 		AverageAtCenter;
> 
> 	GenerateArray( big );
> 	AverageAtCenter = LocalAverage( &big[ S/2 ][ S/2 ] );
> 	printf( "Average at center is %d\n", AverageAtCenter );
> }
> 
> LocalAverage( window )
> 	int	window[S][S],
> 		result;
> {
> 	result = window[-1][0] + window[0][1] +
> 		window[1][0] + window[0][-1];
> 	result /= 4;
> 	return result;
> }

(1) I don't think "result" is declared in the right place.
(2) You're passing an (int *) actual argument to the LocalAverage
function, but you have declared its formal parameter as an SxS array,
which is one level difference of dereferencing.  The formal parameter
is equivalent to
	int	window[][S];
or
	int	(*window)[S];
Because of the way code is generated, you can actually get away
with this type punning in this particular case.