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From: oster@dewey.soe.berkeley.edu (David Phillip Oster)
Newsgroups: comp.sys.mac
Subject: Re: C problem
Message-ID: <21061@ucbvax.BERKELEY.EDU>
Date: Thu, 1-Oct-87 14:36:25 EDT
Article-I.D.: ucbvax.21061
Posted: Thu Oct  1 14:36:25 1987
Date-Received: Mon, 5-Oct-87 07:17:51 EDT
References: <2120@sfsup.UUCP>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster)
Organization: School of Education, UC-Berkeley
Lines: 28

In article <2120@sfsup.UUCP> shap@sfsup.UUCP (J.S.Shapiro) writes:
>I have tried going indirect via register a5 to get at the host
>application's quickdraw globals structure, and that doesn't seem to work.
>If I simply say 'qd.screenBits', I get the a diagnostic.

What you need to do is:

func(){
  qdVarsType *qd; /* I don't know the real name for this type.
		It is not defined in LightSpeed C */

		/* CurrentA5 is a system low-mem global */
		/* it holds a pointer that points to the last qdVar, not 
			the first like everything else does. */
  qd = (qdVarsType *) (CurrentA5 + sizeof(qdVarsType));  

  qd->screenBits  ... /* will access the globals */
...
}

The above trick will also work for LightSpeed C programmers, if they have an
appropriate definition of qdVarsType.

This is all from memory, and may be slightly wrong.

--- David Phillip Oster            --A Sun 3/60 makes a poor Macintosh II.
Arpa: oster@dewey.soe.berkeley.edu --A Macintosh II makes a poor Sun 3/60.
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