Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ukma!kherron
From: kherron@ms.uky.edu (Kenneth Herron)
Newsgroups: comp.lang.pascal
Subject: Re: Turbo Pascal absolute variables crossing units
Keywords: absolute variables units Borland Turbo Pascal TP4.0
Message-ID: <13784@s.ms.uky.edu>
Date: 22 Jan 90 16:27:08 GMT
References: <3757@mit-caf.MIT.EDU> <2013@rwthinf.UUCP>
Reply-To: kherron@ms.uky.edu (Kenneth Herron)
Organization: U of Kentucky, Mathematical Sciences
Lines: 48

In episode <2013@rwthinf.UUCP>, 
we heard pmk@cip-s01.UUCP (Michael Keukert) say:
|In article <3757@mit-caf.MIT.EDU> the@mit-caf.UUCP (Siang-Chun The) writes:
|>
|>	   status : integer absolute inner.stat;
|
|Try instead:
|
|	UNIT outer;
|
|	INTERFACE
|
|	CONST status:INTEGER = inner.stat;
|
|	IMPLEMENTATION
|
|Doing this, you declare outer.status as a typed constant which means,
|this is a "normal" variable but with a defined value within the code.
|
|ABSOLUTE is only valid with a memory-adress for example
|
|       VAR somewhere_in_memory ABSOLUTE $c000:0000;
|
|which means, that the variable somewhere_in_memory contains always
|the value in memory-cell $c000:000.
|
|OK?

BZZT!  Wrong, but thanks for playing...

Your alternative suggestion won't work.  Inner.stat is a variable, so
at compile-time, when status is initialized, inner.stat has no value.
Further, any changes to inner.stat as the program runs would not
be reflected in status.  Your example would work if the declaration
made status use the same memory location as inner.stat.

Your comments about ABSOLUTE are also wrong.  You can give a variable
name in place of the address, in which case the new variable being
defined is aliased to the same memory location as the original variable.
This is, in fact, the correct way of doing what you seem to be trying
in your counterexample (except that evidently it doesn't work across
unit boundaries).

Disclaimer:  The latest version I have programming experience with
is TP 4.0; from what I've heard about the later versions, the above
facts should still be correct.

Kenneth Herron