Message-ID: <390BFDEB.42A8D686@gtcom.net>
From: Krogg <krogg DOT no DOT to DOT spam AT gtcom DOT net>
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Subject: Re: Array swapping.
References: <390B75BB DOT 621F846A AT gtcom DOT net> <390bf4ba DOT 51457508 AT news DOT cis DOT dfn DOT de>
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Date: Sun, 30 Apr 2000 05:33:32 -0400
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To: djgpp AT delorie DOT com
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Horst Kraemer wrote:
> 
> 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.

I know that,but the information about the array is stored
SOMEWHERE,and therefore it should be able to be changed... 

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

I bet you can,I dont know how yet,but i am drinking "Mountian Dew" and
 one day i will stay up long enough to prove it.
 
> 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:

after reading that about 4 times,I an starting to get it.
 
>         float x[100][50];
>         float y[100][50];

Is there some reason you used [100] instead of [50] as
the first subscript?
 
>         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:

Cool,I test it,and this is exactaly the automagic that
i was looking for.You are truly a wizard.
 
> Regards
> Horst

Thanks a lot,I been searching all day for a solution and
though i have found some cool things to read,i never found
a solution till i read your post.Thanks.

BE cool,
 Krogg.


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