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From: vrm@blackwater.cerc.wvu.wvnet.edu (Vasile R. Montan)
Newsgroups: comp.sys.mac.programmer
Subject: Why won't ResError return the right message?
Message-ID: <1696@babcock.cerc.wvu.wvnet.edu>
Date: 6 May 91 14:40:54 GMT
Sender: ab@cerc.wvu.wvnet.edu
Reply-To: un020070@vaxa.wvnet.edu
Lines: 30

I am writing a program which does a lot of reading and writing
of resources (but don't we all? :-).  I am trying to write the
code as defensively as possible, so that if anything goes wrong,
the program will continue as gracefully as possible.  For example,
here is a snip of code from one of my routines:

if OkSoFar then  {If we've run in to no problems so far, then get the}
   begin         {resource and typecast it to the right type.}
    Room := RoomHandle(GetResource('ROOM', RoomNum));
    OSResult := ResError;  {Check for errors.}
    if OSResult <> 0 then  {If there was an error...}
     begin
       doOSErr(OSResult);  {then post an alert}
       OkSoFar := False;   {and stop trying to finish the procedure}
     end;
   end;

As you can see, the soundness of the code relies on ResError to
tell if anything has gone wrong.  However, I tried testing the
code by removing the crucial resource and running this code again.
Even though GetResource couldn'thave found the resource (because
it wasn't there), ResError returned a 0, indicating that nothing
was wrong.  Needless to say, the first time I referred to the
resource, I got a Bus Error exception, because I was following
the invalid handle out into La-La Land.

Why didn't ResError tell me there was a problem?

--Kurisuto
un020070@vaxa.wvnet.edu