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From: decot@hpisod2.HP.COM (Dave Decot)
Newsgroups: comp.lang.c
Subject: Re: A modest proposal
Message-ID: <2550023@hpisod2.HP.COM>
Date: Wed, 29-Jul-87 15:45:28 EDT
Article-I.D.: hpisod2.2550023
Posted: Wed Jul 29 15:45:28 1987
Date-Received: Sat, 1-Aug-87 15:02:16 EDT
References: <1362@cullvax.UUCP>
Organization: Hewlett Packard, Cupertino
Lines: 29

0 is currently not a null pointer constant of any type.

0 is an integer constant that can be assigned to any pointer variable,
or cast to any pointer type, producing a mysterious null pointer value
of the appropriate type.  0 can also be used to initialize pointer
variables to such a mysterious null pointer value.

Pointer-valued expressions can also be compared for equality or inequality
to the appropriate mysterious null pointer value by testing them against
the integer constant 0.

An integer 0 has no other appropriate usage in contexts where a pointer
value is ordinarily required; specifically, it is unusable as an actual
parameter in a function call unless transformed into the appropriate
mysterious null pointer value by a cast.

The language definition does not guarantee that the stored versions of
mysterious null pointer values for different pointer types have the same bit
pattern, or even that they are the same length.  It does not even guarantee
that two null pointers of the same type have the same bit pattern, although
they must appear to be equal when compared to each other and 0.

I see no real benefit to providing a NULL keyword in C, since 0 already
suffices.  If it is desired in ANSI C that 0 be automatically converted
to the appropriate null pointer value when used as an actual parameter
to a function with a prototype in scope, that's fine with me.

Dave Decot
hpda!decot