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/* 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?

On 12/04/2011 0.52, dick wrote:
> struct A
> {
> int a;
> };
>
> struct B1 : public A
> {
> int a;
> };
>
> struct B2 : public A
> {
> int a;
> };
>
> struct C : public B1, public B2
> {
> int a;
> };

If I go on with:

#include <iostream>
int main() {
C ccc;
ccc.a=123;
ccc.B1::a=234;
ccc.B2::a=345;
ccc.B1::A::a=456;
ccc.B2::A::a=567;
std::cout << ccc.a << " " << ccc.B1::a << " "
<< ccc.B2::a << " " << ccc.B1::A::a << " "
<< ccc.B2::A::a;
}

.... and then I compile and run this program, I get as output:
123 234 345 456 567

What's the problem?

--

Carlo Milanesi
http://carlomilanesi.wordpress.com/

>
> What's the problem?
>

My g++ compiler did not compile the code.


What compiler did you use?

On 12/04/2011 1.56, dick wrote:
>>
>> What's the problem?
>>
>
> My g++ compiler did not compile the code.
>
>
> What compiler did you use?

I used Microsoft (R) 32-bit C/C++ Optimizing Compiler version
15.00.30729.01 for 80x86, included with Visual Studio 2008.
Now I just tested it also with g++ 4.3.2 for Linux and actually I got
for 4 times the compilation error: ‘A’ is an ambiguous base of ‘C’.

I think GCC is wrong.

--

Carlo Milanesi
http://carlomilanesi.wordpress.com/

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?

V
--
I do not respond to top-posted replies, please don't ask

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.
>

V
--
I do not respond to top-posted replies, please don't ask

Carlo Milanesi <> writes:
> I think GCC is wrong.

Note that both clang++ (2. and Comeau C++'s online compiler[*] (which
seems to be highly regarded for accurately reflecting the standard) give
the same error as gcc...
[*] http://www.comeaucomputing.com/tryitout

-Miles

--
My books focus on timeless truths. -- Donald Knuth