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From: mneerach@iiic.ethz.ch (Matthias Ulrich Neeracher)
Newsgroups: comp.sys.mac.programmer
Subject: Re: TrapAvailable
Message-ID: <25916@neptune.inf.ethz.ch>
Date: 23 Feb 91 11:41:02 GMT
References: <29004@cs.yale.edu>
Sender: news@neptune.inf.ethz.ch
Reply-To: mneerach@iiic.ethz.ch
Organization: Departement Informatik, ETH, Zurich
Lines: 23

In article <29004@cs.yale.edu>, tarr-michael@CS.YALE.EDU (michael tarr) writes:
>
>When I try to use the call TrapAvailable as per the latest issue of
>MacUser to find out if Gestalt is around, Think C 4.0.2 complains that
>"TrapAvailable" is undefined.
>
>What am I missing?

Simple: There is no such trap as TrapAvailable (yet). A simple method is
to compare the address of the trap, obtained with NGetTrapAddress, with
the trap address of the _Unimplemented trap ($A89F, I believe, but better
look it up). If they are the same, the trap is not available.

While this method works on all reasonably new macs, a more complicated
incantation is needed if you are worried about compatibility with 
64K ROM macs.

Matthias

-- 
Matthias Neeracher                                   mneerach@iiic.ethz.ch
   "These days, though, you have to be pretty technical before you can 
    even aspire to crudeness." -- William Gibson, _Johnny Mnemonic_