Xref: utzoo comp.lang.c++:6797 comp.std.c:2601
Newsgroups: comp.lang.c++,comp.std.c
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: references to dereferenced null pointers
Message-ID: <1990Mar13.175253.15134@utzoo.uucp>
Organization: U of Toronto Zoology
References: <51083@microsoft.UUCP> <25EB8EE8.8462@paris.ics.uci.edu> <52081@microsoft.UUCP> <25F8D2FB.10981@paris.ics.uci.edu> <1990Mar11.015305.28264@utzoo.uucp> <1990Mar11.222634.2701@almira.uucp> <1990Mar12.175613.12082@utzoo.uucp>
Date: Tue, 13 Mar 90 17:52:53 GMT

In article <1990Mar12.175613.12082@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>>... 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...
>
>K&R1 was kind of sloppy about this, partly because the pdp11 let you get
>away with a lot...

Oops, I goofed.  (Yesterday was a bad day...)  There is no problem with
this.  The function is known to return pointer to character, so the
"return(0)" [actually "return(NULL)", prefaced by "#define NULL 0"]
gets compiled as if it were "return((char *)0)" and everything is fine.
By the time the value reaches the caller, it has already been converted
to a pointer.  Automatic conversion in "return" has been in the language
since well before K&R1 (I can remember when it arrived, but that was a
*long* time ago).

On closer inspection of K&R1, at the prodding of a friend, no, K&R1 is
*not* sloppy about this.  I can't find any instance where the rules are
being violated.  Conversion of zero to pointer is always conversion of the
constant 0.
-- 
MSDOS, abbrev:  Maybe SomeDay |     Henry Spencer at U of Toronto Zoology
an Operating System.          | uunet!attcan!utzoo!henry henry@zoo.toronto.edu