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From: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Newsgroups: comp.sys.mac.programmer,comp.sys.mac.hypercard
Subject: Re: XFCN/XCMD string in MPW C v3.0
Message-ID: <12964@dartvax.Dartmouth.EDU>
Date: 8 Apr 89 18:46:26 GMT
References: <kYDWlFy00VQE8JCEES@andrew.cmu.edu>
Sender: news@dartvax.Dartmouth.EDU
Reply-To: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Followup-To: comp.sys.mac.programmer
Organization: Thayer School of Engineering
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In article <kYDWlFy00VQE8JCEES@andrew.cmu.edu> wb1j+@andrew.cmu.edu (William M. Bumgarner) writes:
>I'm in the process of converting a set of XFCN's from LSC to MPW C v3.0.
>
>The LSC code contained inline assembly to set-up and restore the A4 register
>so that global (?) strings could be used...
>
>Something similar must be required in MPW C v3.0, but is A4 valid?  Should I
>use the same inline code (code that worked under a different environment)?
>
     There is no way to implement global variables in non-application
code resources created using MPW C.  You will have to find an
alternate means of storing this information.  I suggest putting
everything in a data structure, and passing the pointer to the data
structure down your function chain.  Strings which are considered
constant, you might want to store in a 'STR#' resource.

     Using A4 as a base for global variables is a hack, anyway.  There
are situations I know of which will invalidate A4, making your global
variables useless.  (Dialog filter procs, for example.)

     There is a package on sumex which you might find useful,
/info-mac/hypercard/xfcn-xcmd-glue.hqx.  It contains source for a
bunch of hypercard XCMDs implemented in MPW C and MPW Pascal.

Earle R. Horton

Graduate Student.  Programmer.  God to my cats.