Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!brutus.cs.uiuc.edu!apple!alan
From: alan@Apple.COM (Alan Mimms)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Interesting problem with GetResource('dctb', id)
Keywords: ResourceManager 'dctb'/'actb' SpecialCase
Message-ID: <5065@internal.Apple.COM>
Date: 6 Nov 89 19:10:18 GMT
References: <232@fwi.uva.nl>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 72

In article <232@fwi.uva.nl> dolf@fwi.uva.nl (Dolf Starreveld) writes:
>
>I am currently working on a program that needs to copy a 'dctb' resource
>from one file to another. Since the program must also copy other resources
>I have written a general purpose "CopyResource" routine. The routine itself
>was extensively tested and seemed to work, but .....
>The copying of the 'dctb' resource was only recently added and things
>started to go wrong. After lots of debugging I found out that after executing
>the following statement:
>	inHandle = GetResource('dctb', 10000);
>"inHandle" contains a valid handle, but not a handle to a resource. I entered
>TMON to find out more and:
>1)	Just before executing the statement the 'dctb' resource is not
>	loaded in the heap.
>2)	Just after the statement, the 'dctb' resource is loaded, but
>	immediately following it, the heap contains another relocatable
>	block of exactly the same size of the resource (48 bytes).
>3)	The GetResource call returns a handle to this last block instead
>	of to the actually loaded resource.
>
>Since my program continues to do a GetResInfo call on the handle returned,
>I get into problems. The handle is not a handle to a resource and the
>call sets ResError != 0. Furthermore, the &resID is set to -1 and the
>&resType is set to four zero bytes. This is what finally causes another
>program using the copied resource file to crash.
>
>I moved the GetResource call to very early in my program (just after ToolBox
>initialization), just to be sure the heap was not already corrupt. I also
>tried using other values for the ID (100 instead of 10000). The net result
>was the same in all cases: two blocks appear on the heap and the wrong
>handle is returned to me.
>
>Is this a bug in the system software? Am I doing something wrong?
>Any suggestions?
>
>BTW. For those who think it is important, I am using THINK C 4.0 on an
>8Mb Mac IIcx, system 6.0.4b15.
>Before you start screaming about using 6.0.4b15, you should know that
>the problems were already there when I still used 6.0.3. I have not tested
>with other versions.
>
>--dolf
>
>Dolf Starreveld  Phone: +31 20 592 5056/+31 20 592 5022, TELEX: 10262 HEF NL
>EMAIL:           dolf@fwi.uva.nl (dolf%fwi.uva.nl@hp4nl.nluug.nl)
>SNAIL:           Dept. of Math. and Computing Science, University of Amsterdam,
>                 Kruislaan 409, NL-1098 SJ  Amsterdam, The Netherlands

SOME version of the system software introduced a "feature" in which
'dctb' and 'actb' resources are CLONED when they're retrieved by GetResource
and related calls.  A colleague of mine discovered this recently.  You
MAY be able to get around this with either Get1Resource calls or with
the sequence

	SetResLoad (false);
	GetResource (...);
	SetResLoad (true);
	LoadResource (...);

Anyone in System Software care to comment?

Also, please note that you really SHOULD go ahead an upgrade to 6.0.4
final since there were a few bugs fixed in the last few versions of
6.0.4 after b15 (I THINK).

Hope this helps.
-- 

Alan Mimms                                      My opinions are generally
Communications Product Development Group        pretty worthless, but
Apple Computer                                  they *are* my own...
"The company has new jobs and Jobs has a new company" -- Harry Anderson