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Path: utzoo!linus!vaxine!wjh12!harvard!elvy
From: elvy@harvard.ARPA (Marc Elvy)
Newsgroups: net.unix-wizards,net.lang.c
Subject: Using NULL as an illegal pointer
Message-ID: <311@harvard.ARPA>
Date: Sun, 1-Jul-84 17:38:14 EDT
Article-I.D.: harvard.311
Posted: Sun Jul  1 17:38:14 1984
Date-Received: Tue, 10-Jul-84 04:33:25 EDT
References: <1273@sri-arpa.UUCP>, <4011@utzoo.UUCP>
Organization: Aiken Computation Lab, Harvard
Lines: 26


While it does not seem to be standard practice in the UNIX world,
all of the C programmers (systems programmers or otherwise) here
have been encouraged to adopt explicit casting of NULL.  Sure, 0
is defined to be an illegal pointer, and every implementation of
NULL which I have ever seen has it equal to 0, but just in case
there exists a machine on which NULL is not an untyped (multityped?)
entity, we cast everything.  Besides, it is good documentation,
and does not break anything.  So my vote goes for

	char *string = (char *) NULL;		and
	return ((char *) NULL);			and
	return ((struct struct_name *) NULL);	etc.

rather than

	char *string = NULL;			and
	return (NULL);

Marc


		      Marc A. Elvy  ( elvy@harvard.{arpa,uucp} )
			     Aiken Computation Laboratory
				  Harvard University