多态：多种形态
#include <iostream>
class Mammal
{
public:
Mammal():age(1) { std::cout << "Mammal constructor ...\n"; }
~Mammal() { std::cout << "Mammal destructor ...\n"; }
void move() const { std::cout << "Mammal, move one step\n"; }
virtual void speak() const { std::cout << "Mammal speak!\n"; }
protected:
int age;
};
class Dog : public Mammal
{
public:
Dog() { std::cout << "Dog constructor ...\n"; }
~Dog() { std::cout << "Dog destructor ..\n"; }
void wagTail() { std::cout << "Wagging tail ...\n"; }
void speak() const { std::cout << "Woof!\n"; }
void move() const { std::cout << "Dog moves 5 steps ...\n"; }
};
int main()
{
Mammal *pDog = new Dog;
pDog->move();
pDog->speak();
return 0;
}
其中，Mammal *pDog=new Dog,创建一个mammal类型的指针，所以使用Move时是调用的mammal中的Move( ),由于speak是虚函数，所以调用dog中重写的speak。
#include <iostream>
class Mammal
{
public:
Mammal():age(1) { }
~Mammal() { }
virtual void speak() const { std::cout << "Mammal speak!\n"; }
protected:
int age;
};
class Dog : public Mammal
{
public:
void speak() const { std::cout << "Woof!\n"; }
};
class Cat : public Mammal
{
public:
void speak() const { std::cout << "Meow!\n"; }
};
class Horse : public Mammal
{
public:
void speak() const { std::cout << "Whinny!\n"; }
};
class Pig : public Mammal
{
public:
void speak() const { std::cout << "Oink!\n"; }
};
int main()
{
Mammal* array[5];
Mammal* ptr;
int choice, i;
for (i = 0; i < 5; i++)
{
std::cout << "(1) dog (2) cat (3) horse (4) pig: ";
std::cin >> choice;
switch (choice)
{
case 1:
ptr = new Dog;
break;
case 2:
ptr = new Cat;
break;
case 3:
ptr = new Horse;
break;
case 4:
ptr = new Pig;
break;
default:
ptr = new Mammal;
break;
}
array[i] = ptr;
}
for (i=0; i < 5; i++)
{
array[i]->speak();
}
return 0;
}
创建一个 mammal 指针数组，每个元素存放的是 mammal 对象的指针，如 pig dog... 什么的，mammal中的speak为虚函数，所以调用派生类中的speak。
在编译阶段，不知道将要创建什么类型的对象，因此无法知道要调用哪个speak方法，ptr指向的对象是在运行阶段确定的，这被称为后期绑定（类似与new的动态内存？）或运行阶段绑定，与此相对的是静态绑定和编译阶段绑定。
