Newsgroups: comp.lang.c
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Is "if (!pointer)" as portable as "if (pointer == NULL)" ???
Message-ID: <1990May2.164647.6591@utzoo.uucp>
Organization: U of Toronto Zoology
References: <1990Apr30.222927.9548@utzoo.uucp> <7180@ncar.ucar.edu>
Date: Wed, 2 May 90 16:46:47 GMT

In article <7180@ncar.ucar.edu> steve@groucho.ucar.edu (Steve Emmerson) writes:
>Doesn't the standard guarantee that there exists an implementation-
>dependent integral type capacious enough to handle the pointer-to-
>integer-to-pointer conversion sequence and return the original pointer?

No.  Indeed, the only reason why you can define NULL to be `(void *)0'
instead of just `0' or `0L' is the possibility that there may not be
an integer type large enough to match the size of a pointer.  (This does
not matter to legal programs, but on many machines you can increase the
odds that a badly-written illegal program will accidentally work if you
make NULL the same size as most pointers.)

>If so, then "unsigned long" would appear to be a safe bet -- there being
>nothing longer.

Does not follow.  An implementation might provide longer types.
-- 
If OSI is the answer, what is |     Henry Spencer at U of Toronto Zoology
the question?? -Rolf Nordhagen| uunet!attcan!utzoo!henry henry@zoo.toronto.edu