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仍在研究继承程序，基类是 Shape 并且有三个派生类：矩形、圆形和方形（方形是从 Rectangle 派生的）。当我通过各自的构造函数设置数据值时，当我显示它们时，我得到每个派生类的数据成员的错误值我要么没有正确设置它们（我的猜测），要么我没有正确显示它们。这是一个代码片段。

class Shape
{
     public:
     Shape(double w = 0, double h = 0, double r = 0)
     {
          width = w;
          height = h;
          radius = r;
     }

     virtual double area() = 0;
     void display();

     protected:
     double width;
     double height;
     double radius;
};

一个派生类：

class Rectangle : public Shape
{
     public:
     Rectangle(double w, double h) : Shape(w, h)
     {
     }

     double area();
     void display();      
};

矩形的显示功能：

double Rectangle::area()
{
    return width * height;
}

这是我的主要（）：

#include<iostream>
#include "ShapeClass.h"

using namespace std;

int main()
{   
    Rectangle r(3, 2);
    Circle c(3);
    Square s(3);

    c.display();
    s.display();
    r.display();


    system ("pause");
    return 0;
}

完成 ShapeClass.cpp：

#include<iostream>
#include "ShapeClass.h"

using namespace std;

double Shape::area()
{
    return (width * height);
}

double Rectangle::area()
{
    return width * height;
}

double Circle::area()
{
   return (3.14159 * radius * radius);
}

double Square::area()
{
    return width * width;
}

void Square::display()
{
    cout << "Side length of square: " << width << endl;
    cout << "Area of square: " << this->area() << endl;
}

void Circle::display()
{
    cout << "Radius of circle: " << radius << endl;
    cout << "Area of circle: " << this->area() << endl;
}

void Rectangle::display()
{
    cout << "Width of rectangle: " << width << endl;
    cout << "Height of rectangle: " << height << endl;
    cout << "Area of rectangle: " << this->area() << endl;
}
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1 回答 1

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You need to make your area() function virtual in Rectangle as well:

class Rectangle : public Shape
{
     public:
     Rectangle(double w, double h) : Shape(w, h)
     {
     }

     virtual double area();
     void display();      
};

Now, also keep in mind that if you want the display() function to be overriden in specific shapes (in your example I see that Rectangle also has a display() function), then you need to make it virtual as well, in both classes:

virtual void display();

Edit: I tried the following code and it worked perfectly. It's based on your code, so there might be a problem with how you built your project or how you compile/link it.

#include <iostream>

using namespace std;

class Shape
{
     public:
     Shape(double w = 0, double h = 0, double r = 0)
     {
          width = w;
          height = h;
          radius = r;
     }

     virtual double area() = 0;
     virtual void display() = 0;

     protected:
     double width;
     double height;
     double radius;
};

class Rectangle : public Shape
{
     public:
     Rectangle(double w, double h) : Shape(w, h)
     {
     }

     virtual double area() { return width * height; }
     virtual void display() 
     {
        cout << "Width of rectangle: " << width << endl;
        cout << "Height of rectangle: " << height << endl;
        cout << "Area of rectangle: " << this->area() << endl;
     }
};



int main(int argc, char* argv[])
{
    Rectangle r(3, 2);

    r.display();

    system ("pause");

    return 0;
}
于 2013-05-10T07:12:12.010 回答