Xref: utzoo comp.lang.c++:6801 comp.std.c:2605
Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.lang.c++,comp.std.c
Subject: Re: references to dereferenced null pointers
Message-ID: <3029@auspex.auspex.com>
Date: 13 Mar 90 18:50:20 GMT
References: <25F8D2FB.10981@paris.ics.uci.edu> <1990Mar11.015305.28264@utzoo.uucp> <1990Mar11.222634.2701@almira.uucp>
Followup-To: comp.std.c
Organization: Auspex Systems, Santa Clara
Lines: 44

>    I beg to differ.  I see where you are coming from with the wording:
>"an integral constant expression with the value 0", but in K&R First edition,
>page 97, there is an explicit example which 0 is returned by a function
>returning a pointer to a character.

Since the compiler knows that the function is supposed to return a "char
*", the compiler knows that the integral constant with the value 0 being
returned by that function should be converted to a null pointer-to-char.
In other words, said function doesn't return an integral value of 0, it
returns a null pointer-to-char.  This conversion is no different from
the conversion in

	char *p;

	p = 0;

or

	extern void foo(char *p);

	foo(0);

or

	char *p;

	if (p == 0)
		...

or even

	char *p;

	if (!p)		/* equivalent to previous example */
		...

The same applies to:

>Also, from the text "C guarantees that no
>pointer that validly points at data will contain zero, so a return value of
>zero can be used to signal an abnormal event,..."

since if your function returns a pointer value, it had better be defined
as doing so....