C/C++中抽象类详解及其作用介绍

#ifndef PROJECT6_SHAPE_H
#define PROJECT6_SHAPE_H

class Shape {
public:
    virtual double area() const {return 0.0;}
    virtual double volume() const {return 0.0;}
    virtual void shapeName() const = 0;
};

#endif //PROJECT6_SHAPE_H

#ifndef PROJECT6_POINT_H
#define PROJECT6_POINT_H

#include <iostream>
#include "Shape.h"
using namespace std;

class Point : public Shape{
private:
    double a, b;
public:
    Point(double p1, double p2) : a(p1), b(p2) {};
    virtual void shapeName() const {  // 对虚函数进行再定义
        cout << "This is point with a = "<< a <<" b = " << b << endl;
    }
};

#endif //PROJECT6_POINT_H

#ifndef PROJECT6_CIRCLE_H
#define PROJECT6_CIRCLE_H

#include <iostream>
#include "Shape.h"
using namespace std;

class Circle : public Shape{
protected:
    double r;
public:
    Circle(double radius) : r(radius) {};
    virtual void shapeName() const {  // 对虚函数进行再定义
        cout << "This is circle with r = "<< r << endl;
    }
};

#endif //PROJECT6_CIRCLE_H

#ifndef PROJECT6_CYLINDER_H
#define PROJECT6_CYLINDER_H

#include <iostream>
#include "Circle.h"
using namespace std;

class Cylinder : public Circle{
private:
    double h;
public:
    Cylinder(double r, double height) : Circle(r), h(height) {};
    virtual void shapeName() const {  // 对虚函数进行再定义
        cout << "This is circle with r = "<< r << " h = " << h << endl << endl;
    }
};

#endif //PROJECT6_CYLINDER_H

#include <iostream>
#include "Shape.h"
#include "Point.h"
#include "Circle.h"
#include "Cylinder.h"
using namespace std;

int main() {
    // 创建对象
    Point point1(1.2, 2.3);  // 点对象
    Circle circle1(2.5);  // 圆对象
    Cylinder cylinder1(3.5, 7);

    point1.shapeName();
    circle1.shapeName();
    cylinder1.shapeName();

    Shape *pt;  // 指向基类的指针
    pt = &point1;
    pt->shapeName();
    pt = &circle1;
    pt->shapeName();
    pt = &cylinder1;
    pt->shapeName();

    return 0;
}