#include <iostream>

using namespace std;

class B
{
public:
  B ( void );
  virtual ~B ( void );
  virtual int g ( int a = 0 );
private:
  int b;
};
B::B ( void ) : b ( 1 )
{
}
B::~B ( void )
{
}
int B::g ( int a )
{
  return ( a + b );
}

class D : public virtual B
{
public:
  D ( void );
  virtual ~D ( void );
  virtual int g ( int a = 0 );
private:
  int d;
};
D::D ( void ) : B ( ), d ( 2 )
{
}
D::~D ( void )
{
}
int D::g ( int a )
{
  return ( a + d );
}

int main ( void )
{
  D d;
  B &b   =  d;
  B *pb  = &d;
  D *pd1 = dynamic_cast < D * > (  pb );  //遵循1
  D &pd2 = dynamic_cast < D & > ( *pb );  //遵循2

  return ( 0 );
}