From -1935017460308067426 X-Google-Language: ENGLISH,ASCII X-Google-Thread: f78e5,f1dec9ce20a9c98f X-Google-Attributes: gidf78e5,public From: James.Kanze@dresdner-bank.com Subject: Re: null pointers (was: Why's of C++ -- Part 1) Date: 1999/08/23 Message-ID: <7prf8u$up8$1@nnrp1.deja.com>#1/1 X-Deja-AN: 516306318 Content-Transfer-Encoding: quoted-printable Approved: Fergus Henderson References: <7opqvm$vpa$1@news.hal-pc.org> <37B7C714.44E4EFB4@lucent.com> <7pcoem$105@abyss.West.Sun.COM> <7pdh80$qaf$1@engnews1.eng.sun.com> <7phdj7$4oj@abyss.West.Sun.COM> <2yG4gOAhsRv3EwJN@robinton.demon.co.uk> X-Original-Date: Mon, 23 Aug 1999 12:36:47 GMT Content-Type: text/plain; charset=iso-8859-1 X-Http-User-Agent: Mozilla/4.06 [de] (WinNT; I) X-Complaints-To: news@news.unimelb.edu.au X-Http-Proxy: 1.0 x27.deja.com:80 (Squid/1.1.22) for client 193.194.7.84 X-Trace: izvestia.its.unimelb.edu.au 935440619 26933 128.250.29.17 (23 Aug 1999 20:36:59 GMT) Organization: Deja.com - Share what you know. Learn what you don't. X-Article-Creation-Date: Mon Aug 23 12:36:47 1999 GMT X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUAN8GwxeEDnX0m9pzZAQF/nQF+Iy2PHvAfDUDBHBOLgrY3bKLZK0hiXHbO MNB+itRT/S4ZrHGnoHZzR+DC5EwLHRUr =9mo7 X-MyDeja-Info: XMYDJUIDkanze Mime-Version: 1.0 NNTP-Posting-Date: 23 Aug 1999 20:36:59 GMT X-MIME-Autoconverted: from 8bit to quoted-printable by ncar.UCAR.EDU id GAA07677 Newsgroups: comp.std.c++ In article <2yG4gOAhsRv3EwJN@robinton.demon.co.uk>, Francis Glassborow wrote: > In article <7phdj7$4oj@abyss.West.Sun.COM>, Stanley Friesen [Contractor] > writes > >The example I was actually objecting to was using a *variable* of > >type int that happened to have the value zero. THAT I find > >unacceptable. And it is certainly not allowed in C, so there is no > >reason from compatibility to accept it in C++. > A further problem has just occurred to me. Given an overload set > including f(int) and f(char *) how do I pass the value of the null > pointer constant to the second one? You don't, of course. Any more than you pass any other literal to a function in general. A value is passed to the function, but whether that value is the result of a literal or not, there is no way for the function to tell. You can, of course, pass a null pointer to the function. > f(0) resolves in a call to f(int) > f((void *)0) falls foul of there being no conversion > f((char *)0) may seem correct but it is not the null pointer constant > and can be coded differently (and, I believe, actually is on some > debugging implementations). When you say "coded differently", what do you mean. The expression "(char*)0" is a null pointer, and must be coded as such. > It seems to me that C++ provides no standard conforming mechanism to > pass a null pointer constant to f(char *) in the presence of any > version of f that can take an integer type argument. A null pointer constant is a compile time construct, and has no meaning at run time. You can pass a null pointer to the function, and that is all that counts. -- James Kanze mailto: James.Kanze@dresdner-bank.com Conseils en informatique orient=E9e objet/ Beratung in objekt orientierter Datenverarbeitung Ziegelh=FCttenweg 17a, 60598 Frankfurt, Germany Tel. +49(069)63198627 Sent via Deja.com http://www.deja.com/ Share what you know. Learn what you don't. --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html ]