Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!uflorida!haven!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: use of NULL
Keywords: NULL zero 0 C Microsoft
Message-ID: <16106@mimsy.UUCP>
Date: 24 Feb 89 10:33:27 GMT
References: <1167@unisec.usi.com. <5312@turnkey.TCC.COM. <9582@smoke.BRL.MIL. <20928@shemp.CS.UCLA.EDU>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 21

In article <20928@shemp.CS.UCLA.EDU> heather@SEAS.UCLA.EDU writes:
>Excuse me for a probably naive question that I've had since following the
>discussion of passing NULL to functions: Why doesn't the C standard
>treat NULL or 0 (a static/constant NULL or 0, i.e. indicated at compile time)
>passed to a function that has a pointer value in the function prototype 
>as a special case and do the cast implicitly?

This is a perfectly reasonable question, with a perfectly reasonable
answer.  It is not a special case and it works just fine.  The key
is the phrase `function prototype':  Not all compilers handle prototypes,
and not all programs include prototypes.

If the compiler does not *know* that the first argument to strtok() has
type `char *', it cannot convert a 0 argument to a nil-pointer-to-char.
It passes an int-0 (or, with Microsoft's `0L' definition, a long-0)
simply because it does not know any better.  Give it the information
(in the form of a prototype declaration, or a cast at invocation, or
both) and it does the conversion.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris