C++ class friend

class A;
class B;
class A
{
public:
	explicit A( int a );
	~A();
	friend class B;
private:
	int aa;
};

A::A( int a )
{
	aa = a;
}

A::~A()
{

}

class B
{
public:
	explicit B( int b );

	void GetValue( A a );
private:
	int bb;
};

B::B( int b )
{
	bb = b;
}

void B::GetValue( A a )
{
	printf( "A::a = %d
", a.aa );
}

int _tmain(int argc, _TCHAR* argv[])
{
	A a(10);
	B b(20);
	b.GetValue( a );
	return 0;
}