hour18_3.cpp

来自「《24学时精通c++》的随书源码的下半部分。欢迎下载学习。」· C++ 代码 · 共 74 行

 // Listing 18.2 - dynamic cast
 #include <iostream>
 using std::cout; // this file uses std::cout
 
 class Mammal
 {
 public:
     Mammal():itsAge(1) { cout << "Mammal constructor...\n"; }
     virtual ~Mammal() { cout << "Mammal destructor...\n"; }
     virtual void Speak() const { cout << "Mammal speak!\n"; }
 protected:
     int itsAge;
 };
 
 class Cat: public Mammal
 {
 public:
     Cat() { cout << "Cat constructor...\n"; }
     ~Cat() { cout << "Cat destructor...\n"; }
     void Speak()const { cout << "Meow\n"; }
     void Purr() const { cout << "rrrrrrrrrrr\n"; }
 };
 
 class Dog: public Mammal
 {
 public:
     Dog() { cout << "Dog Constructor...\n"; }
     ~Dog() { cout << "Dog destructor...\n"; }
     void Speak()const { cout << "Woof!\n"; }
 };
 
 
 int main()
 {
     const int NumberMammals = 3;
     Mammal* Zoo[NumberMammals];
     Mammal* pMammal;
     int choice,i;
     for (i=0; i<NumberMammals; i++)
     {
         cout << "(1)Dog (2)Cat: ";
         std::cin >> choice;
         if (choice == 1)
             pMammal = new Dog;
         else
             pMammal = new Cat;
 
         Zoo[i] = pMammal;
     }
 
     cout << "\n";
 
     for (i=0; i<NumberMammals; i++)
     {
         Zoo[i]->Speak();
 
         Cat *pRealCat =  dynamic_cast<Cat *> (Zoo[i]);
 
    //     if (pRealCat)
             pRealCat->Purr();
    //     else
    //         cout << "Uh oh, not a cat!\n";
    //  You should get a runtime error when you try to get a dog to Purr
    //  You can't dynamicaly cast the wrong object type (dog to cat)
    //  The if test (now commented out) would catch the cast failure and
    //  Warn you that you did not have a cat... 
 
         delete Zoo[i];
         cout << "\n";
     }
 
     return 0;
 }