From: horst DOT kraemer AT gmx DOT de (Horst Kraemer)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Array swapping.
Date: Sun, 30 Apr 2000 08:54:39 GMT
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To: djgpp AT delorie DOT com
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On Sat, 29 Apr 2000 19:52:27 -0400, Krogg <krogg DOT no DOT to DOT spam AT gtcom DOT net>
wrote:

> 
> I got 2 arrays of same type/size.
> 
> float abc[50][50];
> float cba[50][50];
> 
> how can i "swap" them?
> 
> so that abc[x][y] will now point to cba[x][y] and
> vice versa...

abc and cba don't point. Don't believe in fairy tales sine
grandmothers tell you. Arrays are _not_ pointers nor "constant"
pointers. They are arrays. They have meat. They are "data" like ints
or floats or structs.

Therefore you can't "swap" statically allocated arrays without
swapping the data float by float.

You have to define pointers which "correspond" to these arrays - in
the same ways as a pointer to char "corresponds" to a an array of
char. float[50][50] if an array of array of 50 floats. The
corresponding pointer type is the pointer type where the "outer array
type" is transformed to pointer, i.e. a pointer to array of 50 float:

	float x[100][50];
	float y[100][50];


	float (*p1)[50]; 
	float (*p2)[50]; 

	p1 = x;
	p2 = y;

Now you may use p1[3][5]|p2[3][5] in place of x[3][5]|y[3][5] in every
context. In order to "swap" you just swap the pointers:

	void *temp;

	temp = p1 ; p1 = p2 ; p2 = temp:



Regards
Horst