多态的基本语法

#include<iostream>
using namespace std;
//动态多态满足条件
//1.有继承关系
//2.子类要重写父类的虚函数，注意重载是函数名相同但参数不同
//重写 函数返回值类型 函数名 参数列表 完全相同//动态多态的使用
//父类的指针或引用执行子类对象
class Animal {
public://虚函数virtual void speak() {cout << "动物在说话" << endl;}
};
class Dog :public Animal{
public:void speak() {cout << "汪汪叫" << endl;}
};
class Cat :public Animal {
public:void speak() {cout << "喵喵叫" << endl;}};
//地址早绑定，在编译阶段确定函数地址
//如果想执行让猫说话，则函数的地址需要在运行阶段绑定，地址晚绑定
//父类引用指向子类的对象
void doSpeak(Animal &animal) {// Animal &animal = cat;animal.speak();
}
void test01() {Cat cat;Dog dog;doSpeak(cat);doSpeak(dog);
}
void test02() {cout << "sizeof animal = " << sizeof(Animal) << endl;
}int main() {//test01();test02();return 0;
}

案例1——计算器类

#include<iostream>
#include<cstring>
using namespace std;
class Calculator {
public:int getResult(string oper) {if (oper == "+")return m_num1 + m_num2;else if (oper == "-")return m_num1 - m_num2;else if (oper == "*")return m_num1 * m_num2;//如果扩展新功能，需要修改源码//开发中提倡开闭原则//开闭原则:对扩展进行开发，对修改进行关闭}int m_num1;int m_num2;
};
void test01() {Calculator c;c.m_num1 = 10;c.m_num2 = 10;cout << c.m_num1 << "+" << c.m_num2 << "=" << c.getResult("+") << endl;cout << c.m_num1 << "-" << c.m_num2 << "=" << c.getResult("-") << endl;cout << c.m_num1 << "*" << c.m_num2 << "=" << c.getResult("*") << endl;
}//利用多态实现计算器
class AbstractCalculator {
public:virtual int getResult() {return 0;}int m_num1;int m_num2;
};class Add :public AbstractCalculator {
public:int getResult() {return m_num1 + m_num2;}};class Sub :public AbstractCalculator {
public:int getResult() {return m_num1 - m_num2;}};class Mul :public AbstractCalculator {
public:int getResult() {return m_num1 * m_num2;}};
void test02() {//多态使用条件//父类指针或者引用指向子类对象AbstractCalculator* abc = new Add;abc->m_num1 = 100;abc->m_num2 = 100;cout << abc->m_num1 << " + " << abc->m_num2 << " = " << abc->getResult() << endl;delete abc;abc = new Sub;abc->m_num1 = 100;abc->m_num2 = 100;cout << abc->m_num1 << " - " << abc->m_num2 << " = " << abc->getResult() << endl;delete abc;abc = new Mul;abc->m_num1 = 100;abc->m_num2 = 100;cout << abc->m_num1 << " * " << abc->m_num2 << " = " << abc->getResult() << endl;delete abc;}
int main() {//test01();test02();return 0;
}

纯虚函数和抽象类

#include<iostream>
using namespace std;
class Base {
public://纯虚函数//只要有一个纯虚函数，就是抽象类 无法实例化对象virtual void func() = 0;};class Son:public Base {
public://抽象类的子类必须要重写父类中的纯虚函数，否则也属于抽象类void func() {cout << "this is son" << endl;}};void test01() {Base* base = new Son;base ->func();delete base;
}int main() {test01();return 0;
}

案例2——制作饮品

#include<iostream>
using namespace std;
//多态案例2 制作饮品
class AbstractDrinking {
public://煮水virtual void Boil() = 0;//冲泡virtual void Brew() = 0;//导入杯中virtual void PourInCup() = 0;//加入辅料virtual void PutSomething() = 0;void makeDrink() {Boil();Brew();PourInCup();PutSomething();}
};class Cofee :public AbstractDrinking {
public:void Boil() {cout << "煮矿泉水" << endl;}void Brew() {cout << "冲咖啡" << endl;}void PourInCup() {cout << "倒入杯中" << endl;}void PutSomething() {cout << "加点糖" << endl;}};//制作茶叶class Tea :public AbstractDrinking {
public:void Boil() {cout << "煮自来水" << endl;}void Brew() {cout << "放茶叶" << endl;}void PourInCup() {cout << "倒入杯中" << endl;}void PutSomething() {cout << "加柠檬" << endl;}};void doWork(AbstractDrinking &abs) {abs.makeDrink();
}void test01() {Cofee c;Tea t;doWork(c);doWork(t);
}int main() {test01();return 0;
}

虚析构和纯虚析构

#include<iostream>
#include<cstring>
using namespace std;
class Animal {
public:Animal() {cout << "animal构造函数调用" << endl;}//利用虚析构指针可以解决 父类释放子类对象时不干净的问题/*virtual ~Animal() {cout << "animal虚析构函数调用" << endl;}*///纯虚析构 需要声明也需要实现//有纯虚析构函数 也属于抽象类 无法实例化virtual ~Animal() = 0;virtual void speak() = 0;};Animal::~Animal() {cout << "animal纯虚析构函数调用" << endl;
}class Cat :public Animal {
public:Cat(string name) {m_name = new string(name);cout << "cat构造函数调用" << endl;}void speak() {cout << *m_name << "喵喵叫" << endl;}~Cat() {if (m_name != NULL)delete m_name;m_name = NULL;cout << "cat析构函数调用" << endl;}string* m_name;
};void test01() {Animal* a = new Cat("汤姆");a->speak();//父类的指针在析构时 不会调用子类中的析构函数，导致子类如果有堆区属性，会内存泄露。delete a;}int main() {test01();return 0;
}

案例3——电脑组装

#include<iostream>
using namespace std;
class Cpu {
public:virtual void calculator() = 0;
};class VideoCard {
public:virtual void display() = 0;
};class Memory {
public:virtual void storage() = 0;
};
class Intel :public Cpu, public VideoCard, public Memory{
public:void calculator() {cout << "intel cpu正在运行" << endl;}void display() {cout << "intel 显卡正在运行" << endl;}void storage() {cout << "intel 内存正在运行" << endl;}
};class Lenovo :public Cpu, public VideoCard, public Memory {
public:void calculator() {cout << "lenovo cpu正在运行" << endl;}void display() {cout << "lenovo 显卡正在运行" << endl;}void storage() {cout << "lenovo 内存正在运行" << endl;}
};//电脑类
class Computer {
public:Computer(Cpu *c, VideoCard *v, Memory *m) {m_c = c;m_v = v;m_m = m;}void doWork() {m_c->calculator();m_v->display();m_m->storage();}~Computer() {if (m_c != NULL) {delete m_c;m_c = NULL;}//0x000002dde96fc100 {m_c=0x0000000000000000 <NULL> m_v=0x000002dde96fbb68 {...} m_m=0x000002dde96fc3b0 {...} }if (m_m != NULL) {delete m_m;m_m = NULL;}if (m_v != NULL) {delete m_v;m_v = NULL;}cout << "析构函数已执行" << endl;}
private:Cpu* m_c;VideoCard* m_v;Memory* m_m;};void test01() {Cpu* c = new Intel;VideoCard* v = new Intel;Memory* m = new Intel;Computer* computer = new Computer(c, v, m);computer -> doWork();delete computer;
}int main() {test01();return 0;
}

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C++(七)——多态

多态的基本语法

案例1——计算器类

纯虚函数和抽象类

案例2——制作饮品

虚析构和纯虚析构

案例3——电脑组装

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