Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!bbn!mit-eddie!rutgers!dayton!joe
From: joe@dayton.UUCP (Joseph P. Larson)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Ultimate Wait-GetMsg strategy (?)
Message-ID: <6445@dayton.UUCP>
Date: 7 Mar 89 14:45:47 GMT
References: <8902100658.AA16049@postgres.Berkeley.EDU> <6777@polya.Stanford.EDU> <6402@dayton.UUCP> <331@wn2.sci.kun.nl> <562@ivucsb.UUCP>
Reply-To: joe@dayton.UUCP (Joseph P. Larson)
Organization: Dayton-Hudson Dept. Store Co.
Lines: 25

>In article <331@wn2.sci.kun.nl> janhen@wn2.sci.kun.nl (Jan Hendrikx) writes:
>|(!expr) means the same as (expr != 0), which is THE test to test for a 
>|NULL pointer. Even if NULL pointers are internally not represented by
>|all-bits-zero, the compiler must recognize a comparison between a
>|pointer and the constant 0, and emit approprate code in case that that
>|compiler's internal representation of a NULL pointer is not the same
>|as 0.

Irregardless of whether this works or not, it is better style to compare
against NULL, a value that indicates a pointer to nowhere.

What if address zero is a legal address?  NULL might be -1 then.  You don't
know how some odd machine is going to work in the future.

So THE test for comparing a pointer against NULL is to compare it against
NULL, not to depend on what NULL's value might be.  !expr or expr == 0
works, but that is simply because on most machines, NULL is going to be
zero.

-J
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