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From: vinoski@apollo.HP.COM (Stephen Vinoski)
Newsgroups: comp.lang.c++
Subject: Re: virt base c'tor -- my error or CC bug?
Keywords: CC, cfront, 2.0, multiple inheritance, virtual base class
Message-ID: <48359bd1.20b6d@apollo.HP.COM>
Date: 23 Jan 90 16:46:00 GMT
References: <11582@thorin.cs.unc.edu>
Sender: root@apollo.HP.COM
Reply-To: vinoski@zep.UUCP (Stephen Vinoski)
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Organization: Apollo Computer, Chelmsford, MA
Lines: 38

In article <11582@thorin.cs.unc.edu> tuck@jason.cs.unc.edu (Russ Tuck) writes:
>I think I've found a bug in the AT&T C++ 2.0 compiler, cfront, but I'm 
>willing to be shown the error in my code.  On p. 82, section 12.6.2, of
>the C++ (2.0) Reference Manual (AT&T select code 307-146), it says:
>"All sub-objects for virtual base classes are initialized by the constructor
>of the most derived class.  If a constructor of the most derived class
>does not specify a mem-initializer for a virtual base class then that
>virtual base class must have a default constructor or no constructors."
>
>Here's a trivial example program showing this case.
>
>  class V { public: V(int); };
>
>  class A : public virtual V { public: A(); };
>
>  A::A() : V(1) {}
>
>  V v(1);
>  A a;

From Lippman's "C++ Primer", Addison-Wesley, ISBN 0-201-16487-6, page 363:

"A base class specified as virtual must, if it defines any constructors, define
a constructor that does not require an argument list - either a constructor
taking no arguments or one in which default value is provided for each
argument."


-steve

P.S.  IMHO Lippman's "C++ Primer" is the best C++ book going.  If you don't have
it you should get a copy.


| Steve Vinoski                                                                |
| Hewlett-Packard Apollo Division, Testability and Diagnostics Dept.           |
| Chelmsford, MA    01824    (508)256-6600 x5904                               | 
| Internet: vinoski@apollo.com UUCP: {mit-eddie,yale,uw-beaver}!apollo!vinoski |