Cpp抽象类基础实现

CMakeLists.txt

cmake_minimum_required(VERSION 3.16)
project(Share)

set(CMAKE_CXX_STANDARD 11)

include_directories( ./include )
add_executable(Share src/main.cpp src/AbstractShape.cpp include/AbstractShape.h src/Triangle.cpp include/Triangle.h src/Rectangle.cpp include/Rectangle.h)

AbstractShape.h

//
// Created by oceanstar on 2020/8/3.
//

#ifndef SHARE_ABSTRACTSHAPE_H
#define SHARE_ABSTRACTSHAPE_H

/**
 * 抽象形状类
 */
class AbstractShape {
private:
    //私有字段
    int edge;

public:
    //构造函数
    AbstractShape(int edge);

    //实例方法，子类继承后可以重用
    int getEdge();

    //纯虚函数，父类没有实现，调用时只会调用子类的实现
    virtual int calcArea()=0;
};


#endif //SHARE_ABSTRACTSHAPE_H

AbstractShape.cpp

//
// Created by oceanstar on 2020/8/3.
//

#include "AbstractShape.h"


AbstractShape::AbstractShape(int edge)
{
    this->edge = edge;
}

int AbstractShape::getEdge()
{
    return this->edge;
}

Rectangle.h

//
// Created by oceanstar on 2020/8/3.
//

#ifndef SHARE_RECTANGLE_H
#define SHARE_RECTANGLE_H


#include "AbstractShape.h"
/**
 * 矩形类，继承自形状类
 */
class Rectangle: public AbstractShape
{
private:
    //私有字段
    int bottom;
    int height;

public:
    //构造函数
    Rectangle(int bottom, int height);

    //重写父类同名方法，用于实现多态性
    int calcArea();


    void UniqueFunc();
};

#endif //SHARE_RECTANGLE_H

Rectangle.cpp

//
// Created by oceanstar on 2020/8/3.
//

#include 
#include "Rectangle.h"


Rectangle::Rectangle(int bottom, int height) :AbstractShape(4)
{
    this->bottom = bottom;
    this->height = height;
}

int Rectangle::calcArea()
{
    return this->bottom * this->height;
}

void Rectangle::UniqueFunc(){
    std::cout << "UniqueFunc()\n";
}

Triangle.h

//
// Created by oceanstar on 2020/8/3.
//
#include "AbstractShape.h"
#ifndef SHARE_TRIANGLE_H
#define SHARE_TRIANGLE_H


class Triangle : public AbstractShape{
private:
    //私有字段
    int bottom;
    int height;

public:
    //构造函数
    Triangle(int bottom, int height);

    //重写父类同名方法，用于实现多态性
    int calcArea();
};


#endif //SHARE_TRIANGLE_H

Triangle.cpp

//
// Created by oceanstar on 2020/8/3.
//

#include "Triangle.h"

Triangle::Triangle(int bottom, int height) :AbstractShape(3)
{
    this->bottom = bottom;
    this->height = height;
}

int Triangle::calcArea()
{
    return this->bottom * this->height / 2;
}

main中使用：

    Triangle triangle = Triangle(4, 5);
    cout << triangle.getEdge() << ",\t";
    cout << triangle.calcArea() << endl;

    Rectangle rectangle = Rectangle(4, 5);
    cout << rectangle.getEdge() << ",\t";
    cout << rectangle.calcArea() << endl;
    rectangle.UniqueFunc();

    //---------------上转---------------------
    AbstractShape *pShape = NULL; //定义了一个抽象类的指针，注意抽象类不能定义对象但是可以定义指针
    pShape = new Triangle(4, 5); //基类指针指向派生类的对象
    cout << pShape->getEdge() << ",\t";
    cout << pShape->calcArea() << endl;
    delete pShape;//释放了CCirle对象所占的内存，但是指针是没有消失的，它现在就是一个野指针，我们在使用之前必须对它赋值

    pShape = &rectangle; //基类指针指向派生类的对象
    cout << pShape->getEdge() << ",\t";
    cout << pShape->calcArea() << endl;
// 可以看到，我们使用父类的指针调用同一个函数，分别调用了这两个派生类的对应函数，它根据指针指向的类型的不同来决定调用的方法。即使我们以后需要新增加几个类，我们还是这种调用方法，这就是多态的巨大魅力。

    //---------------上转---------------------
    AbstractShape *pShape = NULL; //定义了一个抽象类的指针，注意抽象类不能定义对象但是可以定义指针

    Rectangle *rectangle_bynew = new Rectangle(4, 5);
    cout << rectangle_bynew->getEdge() << ",\t";
    cout << rectangle_bynew->calcArea() << endl;
    rectangle_bynew->UniqueFunc();

    pShape = rectangle_bynew;
    cout << pShape->getEdge() << ",\t";
    cout << pShape->calcArea() << endl;
    delete rectangle_bynew;

 AbstractShape *pShape_1 = new Rectangle(4, 5);
    Rectangle *rectangle_cast = dynamic_cast<Rectangle*>(pShape_1);
    if (rectangle_cast != nullptr)
    {
        cout << "The radius is "
             << rectangle_cast->getEdge() << endl;
    }

等待：

http://blog.chinaunix.net/uid-26921272-id-3360269.html
https://blog.csdn.net/m0_38015368/article/details/71336552
https://www.cnblogs.com/welen/articles/3427379.html
https://blog.csdn.net/lsky380/article/details/102502945
https://blog.csdn.net/weixin_42043407/article/details/106883052
https://blog.csdn.net/shanshenyuyou/article/details/95202112