Xref: utzoo comp.lang.c++:6802 comp.std.c:2606
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From: ken@argus.UUCP (Kenneth Ng)
Newsgroups: comp.lang.c++,comp.std.c
Subject: Re: references to dereferenced null pointers
Message-ID: <1623@argus.UUCP>
Date: 13 Mar 90 20:25:47 GMT
References: <51083@microsoft.UUCP> <25EB8EE8.8462@paris.ics.uci.edu> <1990Mar12.175613.12082@utzoo.uucp>
Organization: NJ Instit. of Tech: TEIES Project
Lines: 27

In article <1990Mar12.175613.12082@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes:
: ANSI C carries forward the rules from K&R1 and later references:  a null
: pointer is an integer *constant* zero converted to a pointer type.  ANSI
: does permit a *constant* expression which evaluates to zero, e.g. "1-1",
: but that does not remove the requirement that the value be known at
: compile time.
[edit]
: >once thought of doing an implementation where NULL != 0, but after further
: >reading convinced myself the implementation would be invalid.
: Not invalid, no; I think there are one or two such.  Unwise, yes, because
: many many programs are sloppy about this and have to be fixed to run on
: such an implementation.

I'm confused, is a non zero NULL pointer valid or not?  I'm not asking if
it will break 90% of the programs out there that use 0 instead of NULL.
On a 370 here I'd love to define NULL as -1 because it will cause an
immediate addressing exception if it is referenced.  But, I was told that
NULL is defined as always being the value zero.

: MSDOS, abbrev:  Maybe SomeDay |     Henry Spencer at U of Toronto Zoology
: an Operating System.          | uunet!attcan!utzoo!henry henry@zoo.toronto.edu


-- 
Kenneth Ng: Post office: NJIT - CCCC, Newark New Jersey  07102
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