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From: russotto@eng.umd.edu (Matthew T. Russotto)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Identifying real handles
Message-ID: <1990Jun5.141748.28953@eng.umd.edu>
Date: 5 Jun 90 14:17:48 GMT
References: <7426@ucdavis.ucdavis.edu>
Sender: news@eng.umd.edu (The News System)
Organization: College of Engineering, Maryversity of Uniland, College Park
Lines: 40

In article <7426@ucdavis.ucdavis.edu> lim@iris.ucdavis.edu (Lloyd Lim) writes:
>This is perhaps not the best thing to do on a Mac but I need to be able to
>tell if some arbitrary long is a real handle in the System heap or the current
>app heap.  I want to keep it relatively clean so I don't want to go looking
>through the heap's internal structures.  Currently, I use the following code:
>
>Boolean ValidHandle(address)
>
>register long address;
>
>{
>   register Boolean  valid;
>   register THz      heapZone;
>   
>   valid = FALSE;
>   if (address && !(address & 1)) {
>      heapZone = HandleZone(address);
>      if (!MemError() && (heapZone == SystemZone() ||
>                          heapZone == ApplicZone())) {
>         valid = TRUE;
>      }
>   }
>   return(valid);
>}
>
>The problem is that this routine can get passed any arbitrary long and that
>some values seem to cause a bus error with HandleZone.  I say "seem" because
>I haven't been able to find a value which causes a bus error in a test program
>but bus errors do occur in the real situation if enough values are examined.
>The real situation is practically unobservable.

Check to see if the handle itself is below BufPtr or MemTop or
whatever variable you feel is appropriate.  If it's below that, there should
never be a bus error.  Then do validity checks on *address, and check to see
if IT is below BufPtr or MemTop. Then call HandleZone.


--
Matthew T. Russotto	russotto@eng.umd.edu	russotto@wam.umd.edu
][, ][+, ///, ///+, //e, //c, IIGS, //c+ --- Any questions?