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NNTP-Posting-Date: Tue, 12 Apr 2011 14:13:39 -0500
From: Pete Becker <pete@versatilecoding.com>
Organization: Roundhouse Consulting, Ltd.
Newsgroups: comp.lang.c++
Date: Tue, 12 Apr 2011 15:13:39 -0400
Message-ID: <2011041215133973606-pete@versatilecodingcom>
References: <bee3f0ea-42ae-4ae4-a254-d5bc9e004f93@k5g2000yqj.googlegroups.com> <2011041214200693759-pete@versatilecodingcom> <io27j5$3v1$1@dont-email.me>
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Subject: Re: // how can I access A::a?
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.c++:3515

On 2011-04-12 15:01:57 -0400, Victor Bazarov said:

> On 4/12/2011 2:20 PM, Pete Becker wrote:
>> On 2011-04-12 13:34:19 -0400, Victor Bazarov said:
>> 
>>> On 4/12/2011 7:38 AM, Pete Becker wrote:
>>>> On 2011-04-11 18:52:40 -0400, dick said:
>>>> 
>>>>> /* multi_level_inheritance.cpp */
>>>>> struct A
>>>>> {
>>>>> int a;
>>>>> };
>>>>> 
>>>>> struct B1 : public A
>>>>> {
>>>>> int a;
>>>>> };
>>>>> 
>>>>> struct B2 : public A
>>>>> {
>>>>> int a;
>>>>> };
>>>>> 
>>>>> struct C : public B1, public B2
>>>>> {
>>>>> int a;
>>>>> };
>>>>> 
>>>>> int main()
>>>>> {
>>>>> C ccc;
>>>>> 
>>>>> ccc.a=123;
>>>>> 
>>>>> ccc.B1::a=456;
>>>>> 
>>>>> /* 0030 */ ccc.B1::A::a=789;
>>>>> 
>>>>> }
>>>>> 
>>>>> // c++ multi_level_inheritance.cpp
>>>>> // multi_level_inheritance.cpp: In function int main():
>>>>> // multi_level_inheritance.cpp:30: error: A is an ambiguous base of C
>>>>> 
>>>>> 
>>>>> // how can I access A::a?
>>>> 
>>>> There are two A::a's, which is why the error message said that the
>>>> reference to A is ambiguous. You need to decide which one you want to
>>>> access, then name it. Hint: there's one in B1 and one in B2.
>>> 
>>> And does the fact that the OP specifically used 'B1::' before 'A::a'
>>> matter not?
>>> 
>> 
>> Sure, but you're giving away the ending. There's clearly a problem in
>> the line ccc.a = 123; so it's not at all likely that the only error
>> message came from the line marked /* 0030 */.
> 
> Actually, since 'C' has a member 'a', which hides *both* 'B1::a' and 
> 'B2::a' (which in turn hid both 'A::a' from base class 'A'), I would 
> not expect to see an error in 'ccc.a = 123;'.  Just saying...
> 
>> 
>> On the other hand, it does help to carefully read the code in question. :-(
>> 
> 

It does help to carefully read the code in question. :-(

-- 
  Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The 
Standard C++ Library Extensions: a Tutorial and Reference 
(www.petebecker.com/tr1book)