Error C2385 on (ctor)

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PLS - 11 Jan 2007 01:37 GMT

I'm converting some C++ code to VC++ 2005 in native (non-managed) mode.
This code doesn't use ATL, but codes the COM mechanisms directly.

It has a class which is the equivalent of ATL's IDispatchImpl:

template<class T>
class CDispatch : virtual public IDispatch, virtual public CUnknown,
private CDispatchBase
{
...

CDispatch::CDispatch(IUnknown *pOuterUnknown)
: CUnknown(pOuterUnknown),
m_pITypeInfo(0)
{}

...
};

The constructor produces this error:

c:\project\pciw\cdisp.h(253) : error C2385: ambiguous access of '{ctor}'
could be the '{ctor}' in base 'IDispatch'
or could be the '{ctor}' in base 'CUnknown'
or could be the '{ctor}' in base 'CDispatchBase'
c:\project\pciw\cdisp.h(285) : see reference to class template
instantiation 'CDispatch<T>' being compiled

I understand about name collisions and disambiguation for methods in
multiple inheritance. How do you disambiguate a constructor?

Seriously, how do I fix this?

Thanks,
++PLS

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Vladimir Nesterovsky - 11 Jan 2007 09:08 GMT

1. Is it correct that CDispatchBase inherits CUnknown (non virtually)? Is it
your intention?
2. Can you define CDispatch constructor this way:

CDispatch::CDispatch(IUnknown *pOuterUnknown)
: CDispatch::CUnknown(pOuterUnknown),
m_pITypeInfo(0)
{}

?

> I'm converting some C++ code to VC++ 2005 in native (non-managed) mode.
> This code doesn't use ATL, but codes the COM mechanisms directly.
[quoted text clipped - 26 lines]
> I understand about name collisions and disambiguation for methods in
> multiple inheritance. How do you disambiguate a constructor?

Thanks.
--
Vladimir Nesterovsky

Reply to this Message

PLS - 11 Jan 2007 21:48 GMT

Changing the constructor as you suggest gives exactly the same error.
And I get that error without the virtuals in the class declaration.

CDispatchBase has no base classes.

IDispatch has IUnknown as a base class.

CUnknown has IUnknown as a base class.

And removing CUnknown and "virtual" from the CDisp base classes gives a
very similar error message:
c:\project\pciw\cdisp.h(253) : error C2385: ambiguous access of '{ctor}'
could be the '{ctor}' in base 'IDispatch'
or could be the '{ctor}' in base 'CDispatchBase'
c:\project\pciw\cdisp.h(284) : see reference to class template
instantiation 'CDispatch<T>' being compiled

I'm stumped. It looks like C++ 2005 just can't handle multiple
inheritance. Any base class is going to have a constructor.

++PLS

> 1. Is it correct that CDispatchBase inherits CUnknown (non virtually)? Is it
> your intention?
[quoted text clipped - 41 lines]
> --
> Vladimir Nesterovsky

Reply to this Message

Ben Voigt - 11 Jan 2007 23:19 GMT

> Changing the constructor as you suggest gives exactly the same error.
> And I get that error without the virtuals in the class declaration.
[quoted text clipped - 15 lines]
> I'm stumped. It looks like C++ 2005 just can't handle multiple
> inheritance. Any base class is going to have a constructor.

Have you tried the Comeau online compiler? If it accepts the code then
Visual C++ definitely has a bug. If not, it may yield a much clearer error
message.

> ++PLS
>
[quoted text clipped - 45 lines]
>> --
>> Vladimir Nesterovsky

Reply to this Message

PLS - 12 Jan 2007 02:02 GMT

> Comeau online compiler

Actually, that helped. Thank you.

Here's what the problem is:

template<class T>
class CDispatch : virtual public IDispatch, virtual public CUnknown,
private CDispatchBase
{
...

CDispatch::CDispatch(IUnknown *pOuterUnknown)
: CUnknown::CUnknown(pOuterUnknown),
m_pITypeInfo(0)
{}

CDispatch::~CDispatch()
{
if (m_pITypeInfo != NULL)
{
m_pITypeInfo->Release();
}
}

...
};

The Comeau compiler tells me:
"ComeauTest.c", line 379: error: qualified name is not allowed in member
declaration
CDispatch::CDispatch(IUnknown *pOuterUnknown)

Remove the "CDispatch::" from these two methods and everything works.

I guess this is a restriction in the new C++ standard. Can anyone
confirm this?

I think this is a compiler bug, because of the horribly off target
message. Can anyone tell me how to file a bug report?

Thanks,
++PLS

Reply to this Message

Ben Voigt - 12 Jan 2007 17:09 GMT

>> Comeau online compiler
>>
[quoted text clipped - 28 lines]
> declaration
> CDispatch::CDispatch(IUnknown *pOuterUnknown)

Oh, your functions are defined inside the class declaration block,
definitely you shouldn't double up the class name.

> Remove the "CDispatch::" from these two methods and everything works.
>
> I guess this is a restriction in the new C++ standard. Can anyone
> confirm this?

I think you were instructing the compiler to look for a nested class.

> I think this is a compiler bug, because of the horribly off target
> message. Can anyone tell me how to file a bug report?

https://connect.microsoft.com/feedback/default.aspx?SiteID=210

> Thanks,
> ++PLS

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Error C2385 on (ctor)

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