Path: utzoo!utgpu!watserv1!watmath!att!dptg!ulysses!andante!alice!shopiro
From: shopiro@alice.UUCP (Jonathan Shopiro)
Newsgroups: comp.lang.c++
Subject: Re: references to dereferenced null pointers
Summary: When is a pointer dereferenced (it matters in C++)
Message-ID: <10582@alice.UUCP>
Date: 16 Mar 90 15:25:26 GMT
References: <51083@microsoft.UUCP> <25EB8EE8.8462@paris.ics.uci.edu> <16179@haddock.ima.isc.com>
Organization: AT&T Bell Laboratories, Murray Hill NJ
Lines: 56



To me the interesting question in this null pointer business is
whether there is any circumstance where it is legal to say *p
where p is a null pointer.

For example, it is definitely legal to write

	void   f(int* p)
	{
		if (p == 0) ...
	}

	int*   x = 0;
	f(x);

It is not obvious (to me) if it is legal in C to write

	void   g(int* p)
	{
		if (&(*p) == 0) ...
	}

	int*   x = 0;
	g(x);

But nobody would write that code anyway, so who cares.

However, in C++ there is an analog that is very likely to be written.

	void   h(int& r)
	{
		if (&r == 0) ...
	}

	int*   x = 0;
	h(*x);

It seems to me that g() and h() are two ways of writing the same thing.
I think it would be nice if they were both legal.

I think the fundamental issue here is when is a pointer dereferenced?
(Since it is clearly illegal to dereference the null pointer).  I don't
se why writing

	*p

alone, or

	&*p

should dereference p.
-- 
		Jonathan Shopiro
		AT&T Bell Laboratories, Warren, NJ  07060-0908
		research!shopiro   (201) 580-4229