Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!cs.utexas.edu!milano!cadillac!pebbles!ned
From: ned@pebbles.cad.mcc.com (CME Ned Nowotny)
Newsgroups: comp.unix.wizards
Subject: Re: Referencing NULL pointers
Message-ID: <1789@cadillac.CAD.MCC.COM>
Date: 18 Jul 89 20:16:47 GMT
References: <32UP02Eg3d=801@amdahl.uts.amdahl.com> <1382@bruce.OZ> <1759@cadillac.CAD.MCC.COM> <18612@mimsy.UUCP>
Sender: news@cadillac.CAD.MCC.COM
Reply-To: ned%cad@MCC.COM (CME Ned Nowotny)
Organization: MCC CAD Program, Austin, TX
Lines: 39

In article <18612@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
=>In article <1759@cadillac.CAD.MCC.COM> ned@pebbles.cad.mcc.com (CME
=>Ned Nowotny) writes:
=>>The argument over whether or not a C compiler should allow dereferencing
=>>of 0 (NULL) or any other numeric constant purporting to be an address is
=>>unrelated to the question of portability.
=>
=>Actually, it is related, other than in the obvious way (the result of
=>
=>	*(sometype *)(some integer expression)
=>
=>is never portable).  The peculiar thing is that, even on machines
=>where location 0 is addressible and has something there (e.g., restart
=>and interrupt vectors), the expression
=>
=>	*(char *)0
=>
=>might get you something from somewhere other than location 0.

...A good example deleted...


Fair enough.  In fact, I would agree that it is never a good idea to
bind an object to a specific address by assigning a numeric constant
(or integer variable) to a pointer variable within a C program.

It is much better to manipulate objects through symbolic names.  Of
course, this requires a good link editor that includes the ability
to bind symbolic names to absolute addresses.  The System V link editor
did provide this capability, but it is baroque and flawed in other
ways.

Does anyone know what, if anything, UI and OSF are doing about the UNIX
link editors they will be providing?

Ned Nowotny, MCC CAD Program, Box 200195, Austin, TX  78720  Ph: (512) 338-3715
ARPA: ned@mcc.com                   UUCP: ...!cs.utexas.edu!milano!cadillac!ned
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