Cpp_part6

1.inheritance 继承

延伸类，子类

class Base {
    int i;

   public:
    Base();
    Base(int ai);
};
Base::Base(int ai) {
    this->i = ai;
}

写该函数必须保留父类默认构造，否则创建子类时会报错

Base::Base() {
    cout << "construct Base" << endl;
}
class Derived : public Base {
    int j;

   public:
    Derived();
    Derived(int ai, int aj);
};
Derived::Derived() {
    cout << "construct Derived" << endl;
}
Derived::Derived(int ai, int aj) : Base(ai) {
    this->j = aj;
    cout << "construct Derived" << endl;
}
void test01() {
    Derived d;
    //构建子类对象会调用父类构造函数，先父后子，析构函数同理（先子后父）
    cout << sizeof(Derived) << endl;
}

class Engine {
    int i;

   public:
    Engine();
    Engine(int ai);
};
Engine::Engine() {
    cout << "construct Engine" << endl;
}
Engine::Engine(int ai) {
    this->i = ai;
    cout << "construct Engine" << endl;
}
class Car {
    Engine e;
    int j;
    int k;

   public:
    Car();
    Car(int m);
    Car(int ai, int aj);
};
Car::Car(int m) : j(m), k(j) {
    //按照变量定义顺序初始化，即k(m),j(k)会出现j为垃圾数的情况
    cout << "test Car" << endl;
    cout << "j:" << j << endl;
    cout << "k:" << k << endl;
}
Car::Car() : e(1) {
    cout << "construct Car" << endl;
}
Car::Car(int ai, int aj) : e(ai) {
    this->j = aj;
    cout << "construct Car" << endl;
}
void test02() {
    Car c;
    Car d(2);
}

2.Polymorphic 多态

多态 Polymorphic:简单而言一行函数可能在不同情况调用不同的代码

class Pet {
    int i;

   public:
    virtual void speak();  //虚函数
    virtual void sleep();
};
void Pet::speak() {
    cout << "Pet::speak" << endl;
}
void Pet::sleep() {
    cout << "Pet::sleep" << endl;
}
// 函数名是函数的首指针
class Cat : public Pet {
   public:
    void speak();
};
void Cat::speak() {
    cout << "miao miao" << endl;
}
class Dog : public Pet {
   public:
    void speak();
};
void Dog::speak() {
    cout << "wang wang" << endl;
}
void handle(Pet& pet) {
    pet.speak();
    // binding:绑定，将一次函数调用与函数入口相对应的过程
    // early binding
    // later binding(runtime binding,dynamic binding)[多态]
    // v-table 虚函数表
    // v-ptr 虚指针

    /*
    // 代码区：函数（代码），常量，lib
    // 全局变量区
    // runtime memory:
    // 1.stack 2.heap
    */
}
void test03() {
    Cat c;
    c.speak();
    handle(c);
    Dog d;
    d.speak();
    handle(d);
    //子类继承关系不要削弱父类的接口
    cout << sizeof(Pet) << endl;
    Cat c1, c2;
    int* p = (int*)&c1;
    cout << *p << endl;
    p = (int*)&c2;
    cout << *p << endl;
}

Main part

#include <bits/stdc++.h>
using namespace std;
int main() {
    test01();
    test02();
    test03();
    return 0;
}