Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!isgate!krafla!aries
From: aries@rhi.hi.is (Reynir Hugason)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Resource path: getting the really most recently opened file?
Message-ID: <1637@krafla.rhi.hi.is>
Date: 14 Apr 90 22:30:13 GMT
References: <11098@hoptoad.uucp>
Organization: University of Iceland
Lines: 43


> So where is this information stored?  It's not stored in TopMapHndl, at
> least not in any obvious way.  TopMapHndl is the map currently at the
> start of the search path, not the file at the beginning of the total
> search path.  And the RM code in the ROM doesn't reference any low
> memory globals other than the documented ones, which don't contain
> this information.

topMapHandle is the front most resource map of all currently open resource
files in the system. UseResFile does _not_ modify this linked-list _ever_.
It simply tells where it should start the search in it, you supply it with
a refNum and it locates that refNum in the list and starts there, slow
but neat.

Consider the following diagram for a more picturesque view of UseResFile.

1. OpenResFile('R0..R3');               2. UseResFile(R2);

    topMapHandle contains                   topMapHandle contains

    (..previously opened files..)           (..previously opened files..)

            R0                                      R0
            R1                                      R1
            R2                                      R2 <- CurResFile
            R3 <- CurResFile                        R3

So as you can see it never modifies the list, and _RsrcZoneInit can
simply walk the list from left to right with-out worrying about what
the current search order is.

Post scriptum: If you need to keep your resource files open in between
application launches (e.g. some INIT doing really niffty stuff) you can
do so by hiding your resource map behind the system resource map. You
will have to NIL your handle fields though, but that's not too though ;-)

==============================================================================
Mimir R. (aries@rhi.hi.is) | A program is like a nose.
Taeknigardur, Dunhaga 5    |       Sometimes it runs, sometimes it blows.
IS-105, Reykjavik          |
ICELAND                    | DISCLAIMER: Who me?!
==============================================================================