#include <iostream> 
using namespace std; 
               
class Base 
{ 
public: 
  virtual Base& operator=(const Base& rhs) //重載操作符可設(shè)為virtual 
  { 
    cout << "Base" << endl; 
    return *this; 
  } 
}; 
               
class Derived : public Base 
{ 
public: 
  //與基類的operator=完全不同，不是重新定義，不會動態(tài)綁定。 
  //如果不定義該操作符，會自動合成一個，并自動調(diào)用基類的operator=，不會動態(tài)綁定 
  Derived& operator=(const Derived& rhs)  
  { 
    cout << "Derived_D" << endl; 
    return *this; 
  } 
               
  //重新定義基類的operator=，會動態(tài)綁定 
  //virtual Base& operator=(const Base& rhs) //返回值兩種都可以 
  virtual Derived& operator=(const Base& rhs)  
  { 
    cout << "Derived_B" << endl; 
    return *this; 
  } 
}; 
               
class Derived2 : public Derived 
{ 
  //此類需要3個operator= 
  //可定義private的copy函數(shù)，由3個operator=調(diào)用 
  //可使用dynamic_cast將基類引用參數(shù)轉(zhuǎn)為子類，并捕獲異常。 
  //如果未發(fā)生異常，則調(diào)用copy，發(fā)生異常則不需賦值 
}; 
               
int main() 
{ 
  Base b1, b2; 
  Derived d1, d2; 
               
  Derived &rd = d1; 
               
  Base &rb1 = b1; //動態(tài)類型為Base 
  Base &rb2 = d2; //動態(tài)類型為Derived 
                 
  rb1 = d1; //輸出"Base" 
  rb2 = d2; //輸出"Derived_B" 
               
  rb1 = rb2; //輸出"Base" 
  rb2 = rb1; //輸出"Derived_B" 
               
  rd = d1; //輸出"Derived_D" 
  rd = b1; //輸出"Derived_B" 
                 
  getchar(); 
  return 0; 
}