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;
}