Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!usc!orion.cf.uci.edu!uci-ics!zardoz!tgate!ka3ovk!drilex!axiom!adelie!mirror!frog!john
From: john@frog.UUCP (John Woods)
Newsgroups: comp.lang.c
Subject: Re: use of if (!cptr) and if (cptr), where cptr is a *
Keywords: * != int
Message-ID: <1650@frog.UUCP>
Date: 19 Jul 89 21:17:00 GMT
References: <10099@mpx2.mpx.com> <93@microsoft.UUCP>
Organization: Misanthropes-R-Us
Lines: 22

In article <93@microsoft.UUCP>, paulc@microsoft.UUCP (Paul Canniff 2/1011) writes:
> >Would (!sptr) break anywhere?  Should it be discouraged?
> It will break if NULL != 0.

It will break if-and-only-if your C compiler is broken.  Read a C book,
preferably the ANSI C spec.

As far as discouragement goes, some feel that treating a pointer like a
boolean is a mixing of abstractions that should be discouraged.  Others
(like myself) feel that treating it as success/failure makes the boolean
interpretation quite natural.

> >	if (sptr= (struct xyzzy *)malloc(...), !sptr)
> >		fatal("cannot malloc");
> 
> This was from a *style* guide?
			Ew, ick, indeed!
-- 
John Woods, Charles River Data Systems, Framingham MA, (508) 626-1101
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