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From: greg@gryphon.CTS.COM (Greg Laskin)
Newsgroups: comp.sys.ibm.pc
Subject: Re: ** Re: MSC 4.0 Large Model ** Original Posters problem solved!!!
Message-ID: <1331@gryphon.CTS.COM>
Date: Tue, 25-Aug-87 22:51:16 EDT
Article-I.D.: gryphon.1331
Posted: Tue Aug 25 22:51:16 1987
Date-Received: Fri, 28-Aug-87 01:04:50 EDT
References: <10400006@altger.UUCP> <72@cunixc.columbia.edu> <1014@bsu-cs.UUCP> <4291@teddy.UUCP> <283@axis.fr>
Reply-To: greg@gryphon.CTS.COM (Greg Laskin)
Organization: Trailing Edge Technology, Redondo Beach, CA
Lines: 58

In article <283@axis.fr> mickey@axis.fr (Michael Dance) writes:
>In article <4291@teddy.UUCP>, jpn@teddy.UUCP (John P. Nelson) writes:
>> 
>> To summarize:  when passing a null pointer to a function, you should
>> always cast the 0 or NULL to the proper pointer type.  In any other
>> context, you may use 0 or NULL interchangably.

CORRECT!

>
>So for functions NULL is the correct thing to pass, this should be cast
>to the correct type if the type is not char * as other pointer types
>may be treated differently on different machines (eg alignment)

WRONG!

>
>As for assignment defined to work with 0 or NULL, this may be true

K&R:
" ... it is guaranteed that assignment of the constant 0 to a pointer
will produce a null pointer distiguishable from a pointer to any object."

>but 
>	char *fred = NULL;
>is clearer than using 0 and only needs 3 extra key-presses so

MATTER OF TASTE but agrees in general with K&R.

>it is surely preferable. Certain machines (eg Motorola sv6350)
>NEED (char *)0 so NULL is shorter to type.

BROKEN COMPILER!


>
>Moral:
>	in general, but not always, things such as NULL may be optional
>	but were defined to avoid the programmer needing to be aware
>	of differences in machine architecture, if you dont use them
>	thats OK but your programs may only work on the machine on which
>	you wrote them

Good moral.  Wrong reason.

K&R:

"C guarantees 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. In general, integers cannot 
meaningfully be assigned to pointers; zero is a special case."
-- 
Greg Laskin   
"When everybody's talking and nobody's listening, how can we decide?"
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