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Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!godot!harvard!seismo!uwvax!gumby!g-frank
From: g-frank@gumby.UUCP
Newsgroups: net.lang,net.lang.mod2
Subject: nil pointer dereferencing
Message-ID: <286@gumby.UUCP>
Date: Tue, 12-Feb-85 09:01:57 EST
Article-I.D.: gumby.286
Posted: Tue Feb 12 09:01:57 1985
Date-Received: Thu, 14-Feb-85 01:49:49 EST
Distribution: net
Organization: U of Wisconsin CS Dept
Lines: 23
Xref: watmath net.lang:1424 net.lang.mod2:164


   Since I don't remember what newsgroup this discussion was in, I'll
try these two . . .

   The Logitech Modula-2/86 compiler for the 8086, as of version 1.1,
has an address constant called NIL which produces the value FFFF:FFFF
(segment:offset).  Since this is not a very valid address on the 
processor (it wraps around into lower memory), no addressability is
lost by this convention.

   Actually, this was in v1.0.  What is new in 1.1 is that, by default,
the compiler generates code to check for a NIL dereferencing operation
before it takes place.  This checking may be turned off by a compile-
time switch.


-- 
      Dan Frank

	  Q: What's the difference between an Apple MacIntosh
	     and an Etch-A-Sketch?

	  A: You don't have to shake the Mac to clear the screen.