Path: utzoo!attcan!uunet!peregrine!elroy!ames!haven!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: pointers, tests, casts
Message-ID: <14694@mimsy.UUCP>
Date: 22 Nov 88 22:53:02 GMT
References: <11130@dartvax.Dartmouth.EDU>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 31

In article <11130@dartvax.Dartmouth.EDU> ericb@libdev (Eric Bivona) writes:
>I know about casting NULL or 0 to get an appropriate nil pointer ...

Note that a cast is always sufficient, if not always necessary.  (I
find that much `extra' casting hampers readability, though.)

[edited]
>	if (ptr == (char *)0) {		/* or (char *)NULL */

>In assignments, a 0 or NULL is cast implicitly to the correct pointer
>type ....

Right.

>What about the '==' comparison above?  Would "(ptr == 0)" get evaluated
>correctly?

It would; the implicit cast occurs here, too.

>... what about ... "(!ptr)"?

That too is correct, by the rule that `!x' means `x == 0'.  Stylistically,
though, I prefer `if (ptr == NULL)'.

In fact, the only place that `0' does not implicitly turn into the right
kind of `nil' is in function calls (and, under dpANS rules, only those
where prototypes are not present or insufficient to convey the necessary
type information).
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris