#include <iostream>

using namespace std;

class Base
{
public:
  Base ( void );
  virtual ~Base ( void );
  virtual int g1 ( int a = 0 );
  virtual int g2 ( int a = 0 );
};
Base::Base ( void )
{
}
Base::~Base ( void )
{
}
int Base::g1 ( int a )
{
  return ( a + 1 );
}
int Base::g2 ( int a )
{
  return ( a + 2 );
}

class Derived : public Base
{
public:
  Derived ( void );
  virtual ~Derived ( void );
  virtual int g1 ( int a = 0 );  //遵循1
  virtual int g2 ( int a );      //遵循2
};
Derived::Derived ( void )
{
}
Derived::~Derived ( void )
{
}
int Derived::g1 ( int a )
{
  return ( a + 11 );
}
int Derived::g2 ( int a )
{
  return ( a + 12 );
}

int main ( void )
{
  int i, j;
  Derived d;
  Base &b = d;

  i = b.g1 ( );
  i = d.g1 ( );
  j = b.g2 ( );
  j = d.g2 ( 0 );

  return ( 0 );
}