From 3876181936551939629 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,4e0e65235aa5eceb X-Google-Attributes: gidf78e5,public From: Colin Rafferty Subject: Re: pointer to member derivation question Date: 1999/06/23 Message-ID: #1/1 X-Deja-AN: 493117151 Approved: stephen.clamage@sun.com (comp.std.c++) References: X-UID: 0000000001 X-Status: $$$T Content-Type: text/plain; charset=us-ascii Organization: - Keywords: derived,base,object,class X-Attribution: > Mime-Version: 1.0 User-Agent: Gnus/5.070084 (Pterodactyl Gnus v0.84) XEmacs/21.2 (Sakuragawa) Newsgroups: comp.std.c++ Originator: clamage@taumet Bill Gibbons writes: > In article , Colin Rafferty wrote: >> I have the following code, and it makes sense to me that it should >> work, but different compilers have different thoughts on the subject. >> >> class Base { /* ... */ }; >> >> class Derived : public Base { /* ... */ }; >> >> class Holder >> { >> public: >> Derived _derived; >> }; >> >> void f() >> { >> Base Holder::* elt = &Holder::_derived; >> } >> >> I don't have a copy of the standard, but the Dec 96 WP seems to say >> nothing about it in either [dcl.mptr] or [conv.mem]. > Pointers to members can be converted implicitly from base to derived but > must be explicitly converted from derived to base (so the above code is > ill-formed). This is backwards from ordinary pointers. I think you are thinking of the opposite thing that I am looking for. I know that I cannot implicitly convert from `Object Derived::*' to `Object Base::*'. This would allow me to refer to a member in Base that is only in Derived. However, this is not what I am doing. I want to convert from `Derived Object::*' to `Base Object::*'. I would like to see a reference to the standard that says that this is not allowed (or that it is allowed). Thanks. -- Colin [ 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 ]