对话框

C++多态

概念

• 允许不同数据类型的对象以统一的接口进行交互。
• 多态是通过函数或运算符的重载（编译时多态）和继承与虚函数（运行时多态）实现
• 提高了程序的扩展性和灵活性。

#include <iostream>
using namespace std;

// 基类People
class People
{
public:
    People(char *name, int age);
    void display();

protected:
    char *m_name;
    int m_age;
};
People::People(char *name, int age) : m_name(name), m_age(age) {}
void People::display()
{
    cout << m_name << "今年" << m_age << "岁了，是个无业游民。" << endl;
}

// 派生类Teacher
class Teacher : public People
{
public:
    Teacher(char *name, int age, int salary);
    void display();

private:
    int m_salary;
};
Teacher::Teacher(char *name, int age, int salary) : People(name, age), m_salary(salary) {}
void Teacher::display()
{
    cout << m_name << "今年" << m_age << "岁了，是一名教师，每月有" << m_salary << "元的收入。" << endl;
}

int main()
{
    Teacher *t = new Teacher("李四", 35, 8000);
    t->m_salary = 10000;
    t->display();
    
    People *p = new Teacher("张三", 30, 5000);
    p->display();

    return 0;
}

• 上方这样书写，p没有实现多态，本质还是People对象，访问的还是People的成员方法和属性。并且不会执行子类Student的析构
• 通过多态可以实现基类对派生类的成员函数的访问(编译看左边，运行看右边【子类】)
• 可以使用虚函数（ virtual关键字）实现运行时多态

运行时多态

• 继承关系
• 子类有重写父类方法(这些方法在基类声明为虚方法virtual，定义时virtual可以不要)
• 存在基类的指针(new或者&)

#include <iostream>
#include <string>
using namespace std;

// 基类People
class People
{
public:
    People(string name, int age);
    virtual void display();
    virtual ~People()
    {
        cout << "People析构函数" << endl;
    }

protected:
    string m_name;
    int m_age;
};
People::People(string name, int age) : m_name(name), m_age(age) {}
void People::display()
{
    cout << m_name << "今年" << m_age << "岁了，是个无业游民。" << endl;
}

// 派生类Teacher
class Teacher : public People
{
public:
    Teacher(string name, int age, int salary);
    void display();
    ~Teacher()
    {
        cout << "Teacher析构函数" << endl;
    }

private:
    int m_salary;
};
Teacher::Teacher(string name, int age, int salary) : People(name, age), m_salary(salary) {}
void Teacher::display()
{
    cout << m_name << "今年" << m_age << "岁了，是一名教师，每月有" << m_salary << "元的收入。" << endl;
}

int main()
{
    People *p = new Teacher("张三", 30, 5000); // 先调用父类构造，然后子类构造
    p->display(); //调用的是基类构造
    delete p;  // 先调用子类，然后父类
    return 0;
}