Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!mcnc!rti!xyzzy!throopw
From: throopw@xyzzy.UUCP (Wayne A. Throop)
Newsgroups: comp.lang.c
Subject: Re: A modest proposal
Message-ID: <162@xyzzy.UUCP>
Date: Tue, 28-Jul-87 17:15:54 EDT
Article-I.D.: xyzzy.162
Posted: Tue Jul 28 17:15:54 1987
Date-Received: Thu, 30-Jul-87 04:28:27 EDT
References: <1362@cullvax.UUCP> <6125@brl-smoke.ARPA>
Organization: Data General, RTP NC.
Lines: 49

> gwyn@brl-smoke.ARPA (Doug Gwyn )
>> drw@cullvax.UUCP (Dale Worley)
>>What I propose is the NULL be made into a keyword of the language
>>which acts like a constant and whose value is a pointer, and
>>eliminating "0" as the null pointer.  As far as I know, no decently
>>written C program will break on this, and it would clean a lot of
>>cruft out of the language definition.

If by "decently written C program", you mean to exclude such things as

        { extern void f();
          f( NULL );
        }

(that is, passing this new keyword as a parameter to a function with no
prototype in scope), then I agree, but wonder where the benefit is?
Clearly, having a typeless NULL keyword will not help portability much,
since pointers of different types are potentially different sizes.

I guess it boils down to the facts that

        1) no decently written program will break on the use of 0 as a
           pointer constant now.
        2) I don't know of a case that is unsafe or nonportable with the
           use of 0 that would be made safe and portable by the use of
           a typeless pointer constant.

> Although I agree with the intent, if 0 were not still guaranteed
> to be equivalent to the null pointer, LOTS of existing applications
> (for example, almost all of UNIX) would break.  Perhaps the best
> approach would be to introduce NULL as a keyword, "deprecate" 0 for
> null pointer (using other words, however), and hope that a future
> revision of the C standard could remove the deprecated feature.
> Unfortunately I suspect that you won't be able to persuade X3J11
> that this is worth doing, but feel free to try.

Well, I agree that 0 must remain.  But I still don't see what the NULL
keyword buys you.  Or perhaps the light dawns: it would issue an error
diagnostic if used as a parameter with no prototype in scope, right?
There might be some small benefit to that, I suppose, but only for newly
minted code.  But for newly minted code, I'd druther kill more birds
with fewer stones by having an option to have the compiler issue a
diagnostic whenever there is no prototype in scope.  So I'm not
enthusiastic about NULL as a keyword.

--
"You have 15 seconds to comply."
        --- out-of-control robot, from RoboCop
-- 
Wayne Throop      <the-known-world>!mcnc!rti!xyzzy!throopw