enum BREED
{
Golden,Teddy,ChineseField
};
class Mammal
{
public:
Mammal(){ cout << "Mammal Constructor!" << endl; }
~Mammal(){cout << "Mammal Destructor!" << endl;}
virtual void speak() const
{
cout << "Mammal speak!" << endl;
}
};
class Dog:public Mammal
{
public:
void speak() const{ cout << "Wang wang..." << endl; }
};
class Cat :public Mammal
{
public:
void speak() const{ cout << "Meow..." << endl; }
};
int _tmain(int argc, _TCHAR* argv[])
{
Mammal* array[2];
array[0] = new Dog();
array[1] = new Cat();
array[0]->speak();//用父类指针指向子类对象,调用虚函数,实现多态
array[1]->speak();
for each (Mammal* ptr in array)
{
if (ptr)
{
delete ptr;
ptr = nullptr;
}
}
}
输出:
Mammal Constructor!
Mammal Constructor!
Wang wang...
Meow...
Mammal Destructor!
Mammal Destructor!
请按任意键继续. . .
附:虚函数工作原理
图1:创建后的dog对象,Dog对象的Manmmal和Dog部分在内存中是相邻的
每一个类都有一个虚函数表,而每个对象都有一个指向虚函数表的指针
图2:Mammal的v-table
调用Dog的构造函数会添加对象Dog部分时,将调整VPTR指针,使其指向Dog类重写的虚函数
图3:Dog的v-table