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Date: Sat, 20 Sep 1997 04:10:45 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199709191810.EAA25970@godzilla.zeta.org.au>
To: bde@zeta.org.au, pst@shockwave.com
Subject: Re: cvs commit: src/gnu/usr.bin/as/config atof-ieee.c src/gnu/usr.bin/ld/rtld rtld.c src/gnu/usr.bin/man/man man.c
Cc: cvs-all@FreeBSD.ORG, cvs-committers@FreeBSD.ORG, cvs-gnu@FreeBSD.ORG,
        jonny@coppe.ufrj.br, phk@FreeBSD.ORG
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>> 	void foo(bar) void *bar; { ... }
>> 	...
>> 	foo(NULL);		/* no prototype in scope */
>> 
>> `lint -p' should warn that the arg is inconsistent, but can't do so if
>> NULL is ((void *)0).
>
>Could you please explain that more clearly?  I see a perfectly good implied
>prototype in scope, and the fact of the matter is that I should not be forced

1. There is no prototype in scope - the function is purposely declared old-
   style so that it does not provide a prototype.
2. The comment is supposed to make this clearer.

>to typecast NULL into a particular pointer type, ever.  Null is well defined
>as a "pointer of some type, with a value of 0"  To me, #define NULL (void *)0
>is the ultimate protection against the misuse of NULL.

No, NULL is macro which expands to an implementation-defined null pointer
constant.  A null pointer constant is either an integral constant expression
with value 0, or such an expression cast to `void *'.  Portable programs
must not assume a particular implementation.  Even if NULL is a pointer
(necessarily of type `void *'), it must be cast to the correct type in
function calls.  The cast is best done by putting a prototype in scope.
Example:

 	void foo();
 	...
		foo((void *)0);		/* no prototype in scope */
 	...
 	void foo(bar) int *bar; { ... }
 
`lint -p' should warn that the arg is inconsistent, but the FreeBSD version
doesn't.  It warns for the equivalent `foo((char *)0)'.

Bruce