Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!decwrl!ucbvax!hoptoad!tim
From: tim@hoptoad.uucp (Tim Maroney)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Calling Code resources?
Message-ID: <6917@hoptoad.uucp>
Date: 7 Apr 89 22:48:37 GMT
References: <11817@ut-emx.UUCP>
Reply-To: tim@hoptoad.UUCP (Tim Maroney)
Distribution: usa
Organization: Eclectic Software, San Francisco
Lines: 36

In article <11817@ut-emx.UUCP> newman@ut-emx.UUCP (David Newman) writes:
>
>Here is another question for the net-gods:  how do you call a
>code resource (like an XCMD or whatever) from another piece of
>code?  Can it be done from a high-level language?  How might it
>be done in Pascal?

In Pascal, you're probably going to need to link in some assembly
language or at least include some INLINEs.  In C, as long as the
code resource follows C coding standards, you can do it all in the
high level language.  Get the resource and lock it down first.
You then have a handle.  The handle indicates a pointer.  Take that
pointer and convert it to a function pointer.  Then call the function
pointer.  Here's an example in MPW C:

	void (*f)();
	Handle res = GetResource('code', 1);
	if (res == 0) return;
	HLock(res);
	f = (void (*))*res;
	(*f)(name);

And here's one in Lightspeed C, which seems to have some problems with
casting things to function pointers (actually, K&R seems ambiguous on
the proper syntax, so I guess we can't blame them):

	long (*f)();
	Handle h = GetResource(TheType, TheID);
	if (h) {
		HLock(h);
		BlockMove(h, &f, 4);
		return (*f)(select, TheID, where, h, p, multi, off);
	}
-- 
Tim Maroney, Consultant, Eclectic Software, sun!hoptoad!tim
This message does represent the views of Eclectic Software.