Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!aplcen!haven!umd5!zben
From: zben@umd5.umd.edu (Ben Cranston)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Low memory globals from C (Was RE:  Finding Screensize under MF)
Summary: Why shouldn't *.h be coded with *(blap*0xXXX) syntax?
Message-ID: <5951@umd5.umd.edu>
Date: 16 Jan 90 01:51:46 GMT
References: <10139@saturn.ucsc.edu> <9429@hoptoad.uucp> <1102@urbana.mcd.mot.com> <10276@saturn.ucsc.edu> <9623@hoptoad.uucp> <4615@helios.ee.lbl.gov>
Reply-To: zben@umd5.umd.edu (Ben Cranston)
Organization: University of Maryland, College Park
Lines: 52

In article <9623@hoptoad.uucp> tim@hoptoad.uucp (Tim Maroney) writes:

> To access low-memory globals from C, if you must, you use the macro
> preprocessor.  For instance, you would say
> #define CurrentA5 (*(long *)0x904)

In article <4615@helios.ee.lbl.gov> beard@ux1.lbl.gov (Patrick C Beard) writes:

> A cleaner way to do low memory globals from THINK C is the ':' notation.
> extern Ptr CurrentA5 : 0x904;
> This method gives you do type checking if you want.

While the ':' notation is very clean and would be nice to have in MPW someday,
can anybody see a reason why the equates in the various *.h files could not
simply be in C access format:

in frump.h:

#define FrumpCount *(short *) 0x1234;

in user code

#include <frump.h>
     FrumpCount = 0;   /* fudge system global */

as it stands now, the equates are just to the numbers and the user program
must supply the cast:

in frump.h:

#define FrumpCount 0x1234;

in user code

#include <frump.h>
     *(short * FrumpCount) = 0;

In other words, can anybody see a profitable use for the address as a plain
integer rather than a cast item?  Actually, one could probably recover the
integer for most purposes simply by using the   &FrumpCount  construct...
(except for compile time values with stupid compilers).

Is there any reason for using the simple number equates other than a bad
case of assembly language hangover?

(utmost apologies to whatever actually lives at 0x1234...)

-- 
Sig     DS.L    ('ZBen')       ; Ben Cranston <zben@Trantor.UMD.EDU>
* Network Infrastructures Group, Computer Science Center
* University of Maryland at College Park
* of Ulm