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From: ridder@elvira.enet.dec.com (Hans Ridder)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Mutual Exclude Gadgets
Keywords: Gadgets
Message-ID: <555@shodha.dec.com>
Date: 29 Dec 89 16:39:37 GMT
References: <947@lpami.wimsey.bc.ca> <22023@usc.edu>
Sender: news@shodha.dec.com
Organization: Digital Equipment Corporation, Customer Support Center
Lines: 37

In article <22023@usc.edu> papa@pollux.usc.edu (Marco Papa) writes:
>Most data structures (including Gadgets) have "user defined" fields at
>the end of them.  That's where you can fool with.  In any case it is
>very easy to build "custom user gadgets", with whatever additional
>fields you want by creating your own modified structure:
>
>struct MyGadget {
>	struct Gadget gad;
>	long extension1;
>	char *extension2;
>	BOOL togglegad;
>}
>
>This is portable, and will work with future releases as well.
                                      ^^^^^^^^^^^^^^^
Just one question.  What if Commodore adds some stuff to the Gadget
structure making it larger?  You'd have to re-compile your code with
new includes, or else their new larger Gadget structure would overlay
your "extensions".  So really, the *binary* code could possibly not
work with future releases.  No?

I think your first sentence above was right on the mark though.

I would suggest using the "User" field directly, or as a pointer to
your extension structure.  Then future changes to the size of a
structure would not affect you, and your *binary* would be compatible.

>-- Marco Papa 'Doc'

-hans



========================================================================
  Hans-Gabriel Ridder			Digital Equipment Corporation
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