From: "Ole Laursen" <ole_laursen AT hardworking DOT dk>
Newsgroups: comp.os.msdos.djgpp
References: <37a49d74 AT news DOT ismi DOT net>
Subject: Re: BITMAP pointers w/ Allegro.
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Date: Sun, 1 Aug 1999 23:07:34 +0200
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To: djgpp AT delorie DOT com
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> main(void)
> {
>    BITMAP *bmp;
>    function(bmp);
> }
>
> function(BITMAP *bmp)
> {
>    bmp = create_bitmap(320, 240);
> }
>
> How do I pass the bitmap by reference so I can edit its value in
> sub-functions?

This will do, I think (warning: I haven't tested it, might have made a
mistake):

main(void)
{
  BITMAP *bmp;
  function(&bmp);      // passing address
}

function(BITMAP **bmp) // getting pointer to pointer to BITMAP
{
  *bmp = create_bitmap(320, 240); // first dereference, then assign
}

So you use a pointer to a BITMAP-pointer to refer to the address of the
BITMAP-pointer variable, thereby being able to change the variable. There
are other possibilities, too, e.g. if you had been using C++ you could have
used a reference with a '&'.


--
Ole Laursen - http://sunsite.auc.dk/olau/
Row, row, row your boat, gently down the streeaam (gee!)