Class dependency/declaration problem

//Declarations (that do not work)
class A;
class B;

//Definition of class A
class A {
protected:
	~A() {
		if(m_b != NULL) {
			m_b->Release();
			m_b = NULL;
		}
	}
	
public:
	A() : m_iRefs(0), m_b(NULL) { };
	void CreateB(B**_b) {
		*_b = new B(*this);
		(*_b)->AddRef();
		this->AddRef();

		if(m_b != NULL) {
			m_b->Release();
			m_b = NULL;
		}

		m_b = *_b;
		m_b->AddRef();
	};
	void AddRef() { m_iRefs++; }
	void Release() {
		if(--m_iRefs <= 0) {
			delete this;
		}
	};
	
private:
	unsigned int m_iRefs;
	B *m_b;
}

//Definition of class B
class B {
protected:
	~B() {
		m_a.Release();
	}
	
public:
	B(A &_a) : m_iRefs(0), m_a(_a) { };
	void AddRef() { m_iRefs++; }
	void Release() {
		if(--m_iRefs <= 0) {
			delete this;
		}
	};

private:
	unsigned int m_iRefs;
	A &m_a;
}

int main() {
	A *a = new A();
	B *b = NULL;
	a->CreateB(&b);

	b->Release();
	a->Release();
}