Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!rutgers!sunybcs!bingvaxu!leah!uwmcsd1!marque!ddsw1!gryphon!greg
From: greg@gryphon.CTS.COM (Greg Laskin)
Newsgroups: comp.sys.ibm.pc
Subject: Re: ** Re: MSC 4.0 Large Model ** NULL isn't always 0
Message-ID: <1332@gryphon.CTS.COM>
Date: Tue, 25-Aug-87 23:11:16 EDT
Article-I.D.: gryphon.1332
Posted: Tue Aug 25 23:11:16 1987
Date-Received: Fri, 28-Aug-87 01:37:40 EDT
References: <10400006@altger.UUCP> <72@cunixc.columbia.edu>
Reply-To: greg@gryphon.CTS.COM (Greg Laskin)
Organization: Trailing Edge Technology, Redondo Beach, CA
Lines: 57

In article <158@dolphy.UUCP> jmg@dolphy.UUCP (Jeffrey Greenberg) writes:
>/**/
>
>You SHOULD use NULL instead of 0 or 0L etc. because things like
>	char *x;
>	x = (char *) NULL;
>does not mean that the address that x is pointing to is address 0.
>It is not true on all machines... Any code you write like this
>won't run on a Sun machines to name one.  This is a machine/OS dependency.

This code will work fine on a Sun machine.  It will produce the
same result as:
char *x
x=0;

If it did not, NULL would have been incorrectly defined.

>If you do things like,
>
>	char *x, dog;
>	if( !x )		/* This is wrong... not portable */
>		x = &dog;
>
>because it is not true between machines/os and your code will fail.

If this is not true, you are not using a C compiler.
K&R:
"The result of the logical negation operator ! is 1 if the value of its
operand is 0, 0 if the value of its operand is non-zero. ... It is
applicable to any arithmetic type or to pointer".

A null pointer is a pointer to which the constant 0 has been assigned.
NULL is user to clearly indicate a special pointer value of 0.

>
>The unspeakable 'far' & 'near' stuff that microsoft uses is a kludge for dealing
>with 16bit machines and 32bit addressing.

There is no compilation model that requires the use of the keywords "far"
and "near" to produce a correctly working program.  Those keywords are
available, if enabled at compilation time, to permit finer tuning
of programs, if desired.  It would not be a bad practice to define these
extended keywords:

#define FAR far
#define NEAR near
#define HUGH hugh

in a header file so that they would be convenienly removable in environments
where they have no effect.

-- 
Greg Laskin   
"When everybody's talking and nobody's listening, how can we decide?"
INTERNET:     greg@gryphon.CTS.COM
UUCP:         {hplabs!hp-sdd, sdcsvax, ihnp4}!crash!gryphon!greg
UUCP:         {philabs, scgvaxd}!cadovax!gryphon!greg