Question regarding virtual inheritance

[Shvalb]

Hi,
I have the following classes:

class A
{
public:
virtual bool	ZeroBalance() const			= 0;
virtual BALANCE	operator=(const BALANCE lAmount)	= 0;
};

class B : public A
{
public:
virtual void	Reserve(const BALANCE lAmount)             = 0;
virtual void	Commit()				= 0;
};

class C : public A
{
virtual bool               ZeroBalance() const		        { return false; }
virtual BALANCE	operator=(const BALANCE lAmount)   { return 0; }
};

and I need a new class:
class D : public C, public B
{
virtualvoid	               Reserve(const BALANCE lAmount)	{ }
virtual void	Commit()				{ }
};

it gives me compilation errors, so I added "virtual" in class B and in class C and still it's not good, it claims ambiguity problems...How can I solve this ??

[Skizmo]

Class A has pure virtual functions that need to be implemented by the inherting class. Class B, same story. Class B doesn't implement the pure virtual functions from class A. Class C is implementing the pure virtual functions from Class A correctly. Class D inherits class C and B. That's not possible because class C and B are both derived from class A, this means that there could be duplicate functions, so the compiler probably doesn 't compile it.

[Shvalb]

I didn't implement the functionality of class A in class B because it's the same functionality as in class C which also derives class A. I wanted to reuse the code of class C.

[D_Drmmr]

it gives me compilation errors, so I added "virtual" in class B and in class C and still it's not good, it claims ambiguity problems...How can I solve this ??

Where did you add the virtual keyword? It would be much easier if you could just provide a complete example, instead of a code snippet.
I compiled this using virtual inheritance under MS VS2005 and it compiled with 2 warnings:

main.cpp(27) : warning C4250: 'D' : inherits 'C::C::ZeroBalance' via dominance
        main.cpp(19) : see declaration of 'C::ZeroBalance'
main.cpp(27) : warning C4250: 'D' : inherits 'C::C::operator =' via dominance
        main.cpp(20) : see declaration of 'C::operator ='

I didn't implement the functionality of class A in class B because it's the same functionality as in class C which also derives class A. I wanted to reuse the code of class C.

Inheritance is not the best means to achieve code reuse. Polymorphism is a means to achieve abstraction.
Your design looks peculiar to me, though I can't tell much from class names like A, B, C. Why is B derived from A?

[Igor Vartanov]

it claims ambiguity problems...

Nope. Nothing but warnings with VC++ 8 (aka 2005).

// 65.cpp
typedef int BALANCE;

class A
{
public:
virtual bool          ZeroBalance() const			= 0;
virtual BALANCE  operator=(const BALANCE lAmount)	= 0;
};

class B : public A
{
public:
virtual void	Reserve(const BALANCE lAmount)             = 0;
virtual void	Commit()				= 0;
};

class C : public A
{
virtual bool          ZeroBalance() const	{ return false; }
virtual BALANCE  operator=(const BALANCE lAmount) { return 0; }
};

class D : public C, public B
{
virtual void	Reserve(const BALANCE lAmount)	{ }
virtual void	Commit()				{ }
};

D:\Temp\65>cl 65.cpp /c /Wall
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.762 for 80x86
Copyright (C) Microsoft Corporation.  All rights reserved.

65.cpp
65.cpp(20) : warning C4100: 'lAmount' : unreferenced formal parameter
65.cpp(25) : warning C4100: 'lAmount' : unreferenced formal parameter
65.cpp(19) : warning C4514: 'C::ZeroBalance' : unreferenced inline function has been removed
65.cpp(20) : warning C4514: 'C::operator =' : unreferenced inline function has been removed
65.cpp(25) : warning C4514: 'D::Reserve' : unreferenced inline function has been removed
65.cpp(26) : warning C4514: 'D::Commit' : unreferenced inline function has been removed

How can I solve this ??

Just never let this ("diamond" inheritance) happen, ever. In case you run into that again, you know your design is wrong.