c++-纯虚函数和抽象类

纯虚函数和抽象类

• C面向接口编程和C多态
  • 函数类型语法基础
  • 函数指针做函数参数(回调函数)思想剖析
  • 函数指针做函数参数两种用法（正向调用、反向调用）
• 纯虚函数 抽象类
  • 抽象类基本概念
  • 抽象类在多继承中的应用
  • 面向抽象类编程案例强化
  • C面向接口编程和C多态

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>

using namespace std;

//图形类
//如果说一个类 拥有一个纯虚函数
//就称这个类是一个抽象类。
//不管这个类中有没有成员属性，只要这个类有纯虚函数，就是一个抽象类， 抽象类就是不能够实例化的。
class Shape
{
public:
    //求图形面积的方法
    //表示图形类声明一个方法getArea（），它是一个纯虚函数，没有函数的实现。
    virtual double getArea() = 0;
};

//三角形
class Tri :public Shape
{
public:
    Tri(int a, int h)
    {
        this->a = a;
        this->h = h;
    }
    virtual double getArea() {
        cout << "三角形求面价" << endl;
        return 0.5*a*h;
    }

private:
    int a;
    int h;
};

//正方形：
//如果说一个普通类，继承拥有纯虚函数的类，如果说不重写纯虚函数，依然是一个抽象类。
//依然不能被实例化， 如果想实例化， 必须要重写这个父类中所有纯虚函数
class Rect : public Shape
{
public:
    Rect(int a) {
        this->a = a;
    }
    virtual double getArea() {
        cout << "正方形求面积" << endl;
        return a*a;
    }
private:
    int a;//正方形边长
};

class Circle :public Shape
{
public:
    Circle(int r)
    {
        this->r = r;
    }

    virtual double getArea()
    {
        cout << "圆形求面积" << endl;

        return 3.14*r * 4;
    }

private:
    int  r;
};

//面向抽象类写一个架构函数
void printArea(Shape *sp)
{
    sp->getArea();
}

//业务层  面向的抽象类编程
int main(void)
{
    //main 中所有使用的变量类型 都是 抽象类Shape的类型。
    Shape *sp1 = new Rect(10);
    //sp1->getArea();

    Shape *sp2 = new Circle(20);
    //sp2->getArea();

    Shape *sp3 = new Tri(10, 20);
    //sp3->getArea();

    printArea(sp1);
    printArea(sp2);
    printArea(sp3);

    return 0;
}

上一个知识的小练习

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>

using namespace std;

//大哥的虚衔
class BigBrother
{
public:
    //会打人。
    virtual void fightPeople() = 0;
};

//东方不败
class EastNeverLose :public BigBrother
{
public:
    virtual void fightPeople()  {
        cout << "使用了葵花宝典区打人" << endl;
    }
};

//无崖子
class Wuyazi :public BigBrother
{
public:
    virtual void fightPeople()  {
        cout << "使用北冥神功打人" << endl;
    }
};

//boss
int main(void)
{
    BigBrother *bigbrother = new Wuyazi;

    //大哥你给我去打人。
    bigbrother->fightPeople();

    delete bigbrother;

    return 0;
}

纯虚函数和多继承

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>

using namespace std;

//接口1
class Interface1
{
public:
    virtual void func1(int a, int b) = 0;
    virtual void func3(int a, int b) = 0;
};

//接口2
class Interface2
{
public:
    virtual void func2(int a) = 0;
};

class Child :public Interface1, public Interface2
{
public:
    virtual void func1(int a, int b)
    {
        cout << "func1" << endl;
    }
    virtual void func3(int a, int b) {
        cout << "func3" << endl;

    }

    virtual void func2(int a)
    {
        cout << "func2 " << endl;
    }
};

int main(void)
{
    Interface1 *if1 = new Child;

    if1->func1(10, 20);
    if1->func3(100, 200);

    Interface2 *if2 = new Child;

    if2->func2(10);

    return 0;
}

电脑组装--小练习

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>

using namespace std;

//--------  抽象层---------
//抽象CPU类
class CPU
{
public:
    CPU();
    virtual void caculate() = 0;
};

//抽象的card类
class Card
{
public:
    virtual void display() = 0;
};

//抽象的内存类
class Memory
{
public:
    virtual void storage() = 0;
};

//架构类
class Computer
{
public:
    Computer(CPU *cpu, Card *card, Memory *mem)
    {
        this->cpu = cpu;
        this->card = card;
        this->mem = mem;
    }

    void work()
    {
        this->cpu->caculate();
        this->card->display();
        this->mem->storage();
    }

    ~Computer() {
        if (this->cpu != NULL) {
            delete this->cpu;
        }
        if (this->card != NULL) {
            delete this->card;
        }
        if (this->mem != NULL) {
            delete this->mem;
        }
    }
private:
    CPU* cpu;
    Card*card;
    Memory *mem;
};
// --------------------------

//-----------实现层----------
//具体的IntelCPU
class IntelCPU :public CPU
{
public:
    virtual void caculate() {
        cout << "Intel CPU开始计算了" << endl;
    }
};

class IntelCard :public Card
{
public:
    virtual void display() {
        cout << "Intel Card开始显示了" << endl;

    }
};

class IntelMem :public Memory {
public:
    virtual void storage() {
        cout << "Intel mem开始存储了" << endl;

    }
};

class NvidiaCard :public Card
{
public:
    virtual void display() {
        cout << "Nvidia 显卡开始显示了" << endl;
    }
};

class KingstonMem :public Memory {
public:
    virtual void storage() {
        cout << "KingstonMem 开始存储了" << endl;
    }
};

//--------------------------

//--------业务层-------------------
int main(void)
{
    //1 组装第一台intel系列的电脑
#if 0
    CPU *intelCpu = new IntelCPU;
    Card *intelCard = new IntelCard;
    Memory *intelMem = new IntelMem;

    Computer *com1 = new Computer(intelCpu, intelCard, intelMem);

    com1->work();

    Card *nCard = new NvidiaCard;
    Memory* kMem = new KingstonMem;

    Computer *com2 = new Computer(intelCpu, nCard, kMem);

    com2->work();

    delete intelCpu;
#endif
    Computer *com1 = new Computer(new IntelCPU, new IntelCard, new IntelMem);
    com1->work();
    delete com1;

    return 0;
}

原文地址：https://www.cnblogs.com/ygjzs/p/12079568.html