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From: root@hobbes.UUCP (John Plocher)
Newsgroups: comp.sys.ibm.pc
Subject: Re: ** Re: MSC 4.0 Large Model ** Original Posters problem solved!!!
Message-ID: <187@hobbes.UUCP>
Date: Fri, 21-Aug-87 19:55:14 EDT
Article-I.D.: hobbes.187
Posted: Fri Aug 21 19:55:14 1987
Date-Received: Sun, 23-Aug-87 10:18:20 EDT
References: <10400006@altger.UUCP> <72@cunixc.columbia.edu> <1014@bsu-cs.UUCP> <3352@zen.berkeley.edu>
Reply-To: root@hobbes.UUCP (John Plocher)
Followup-To: comp.sys.ibm.pc
Organization: U of Wisconsin - Madison  Spanish Department
Lines: 65

+---- Tim Iverson writes the following in article <3352@zen.berkeley.edu> ----
| Nick Christopher writes:
| >	1) Use NULL not 0 as often as applicable.

why?

| Rahul Dhesi writes:
| >Actually, I suggest simply casting 0 or NULL, whichever you use, to
| >the correct type when passing it as a parameter.  When simply using
| >it for a comparison, a cast is not necessary and either may be used.
| 
| A cast is necesary for a comparison with large model pointers in
			   ----------
| both lattice C and MSC4.0.
+----

nooooooooo!  Rahul is completely correct.

The correct definition for NULL is:

#define NULL	0	/* NOT 0L !!! */

K&R page 97:  "C guarentees that no pointer that validly points at data
will contain zero, so a return value of zero can be used to signal an 
abnormal event ... .  We write NULL instead of zero, however, to indicate
more clearly that this is a special value for a pointer."

Note: zero, not (long) 0 or 0L.

The only time one MUST cast NULL is when it is used as a parameter to
a function, as in:

	foo( (char *) NULL );

In this case it is best to cast all pointers AND other non-int values.


K&R Page 41:  "Implicit arethmetic conversions work much as expected. ...
... for each arethmetic operator, the following sequence of conversion rules
is applied:"

	  If
	one is		Convert it to
	------		-------------
	char	 	int
	short		int
	float		double

	Then if
	one is		Convert other to	Result
	------		----------------	------
	double  	double			double
	long		long			long
	unsigned	unsigned		unsigned

	Otherwise the operands must be INT, and the result is INT

K&R Page 49 expressly includes == and != as operators.


(I'd say more, but a large lightning storm just came up and the systems
are shutting down...)

-- 
John Plocher uwvax!geowhiz!uwspan!plocher  plocher%uwspan.UUCP@uwvax.CS.WISC.EDU