类的继承

[Yanger_xy]

#include <iostream.h>

//#define pi 3.1415926
double const pi = 3.1415926;

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

//define a Point class

class Point:public Shape
{
public:
    Point (double x=0, double y=0):point_x(x), point_y (y) {}
    virtual void shap_name () const;
    friend ostream & operator << (ostream & output, const Point & p);
    virtual void set_point ();
    virtual void get_point () const;
protected:
    double point_x;
    double point_y;
};

void Point::shap_name () const
{
    cout << "Point:" << endl;
}

void Point::set_point ()
{
    cout << "Please set the points:";
    cin >> point_x >> point_y;
}

void Point::get_point () const
{
    cout << "(" << point_x << ',' << point_y <<  ")" << endl;
}
ostream & operator << (ostream & output, const Point & p)
{
    output << "(" << p.point_x << ',' << p.point_y <<  ")" << endl;
    return output;
}

//define a Circle class

class Circle:public Point
{
public:
    Circle (double x, double y, double r):Point (x, y), radius (r) {}
    void set_radius ();
    double get_radius () const;
    virtual double area () const;
    virtual void shap_name () const;
    friend ostream & operator << (ostream &output, const Circle &c);
protected:                    //保护成员在派生类中可以被引用，而私有成员则不能！
    double radius;
};

void Circle::shap_name () const
{
    cout << "Circle:" << endl;
}

void Circle::set_radius ()
{
    cout << "Please set the radius of the circle:" << endl;
    cin >> radius;
    
}

double Circle::get_radius () const
{
    return radius;
}

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

ostream & operator << (ostream &output, const Circle &c)
{
    output << '(' << c.point_x << ',' << c.point_y << ')' << "radius = " << c.radius << endl;
    return output;
}

//Define a Cylinder class

class Cylinder:public Circle
{
public:
    Cylinder (double x, double y, double r, double h):Circle (x, y, r), height (h) {}
    void set_height ();
    void get_height () const;
    virtual double area () const;
    virtual double volum () const;
    virtual void shap_name () const;
    friend ostream & operator << (ostream &output, Cylinder &cy);
private:
    double height;
};

void Cylinder::shap_name () const
{
    cout << "cylinder:" << endl;
}

void Cylinder::set_height ()
{
    cout << "Please set the height of the cylinder:" << endl;
    cin >> height;
}

void Cylinder::get_height () const
{
    cout << height << endl;
}

double Cylinder::area () const 
{
    return (2*Circle::area () + 2*pi* Circle::get_radius () *height);
}

double Cylinder::volum () const 
{
    return (Circle::area () * height);
}

ostream & operator << (ostream &output, Cylinder &cy)
{
    output << '(' << cy.point_x << ',' << cy.point_y << ')' << "radius = " << cy.radius
        << "volum = ";
    cy.volum ();
    return output;
}

void main ()
{
    Point point (3.2, 4.5);
    Circle circle (2.4, 1.2, 5.6);
    Cylinder cylinder (3.5, 6.4, 5.2, 10.5);
    
    point.shap_name ();
    cout << point;
    
    circle.shap_name ();
    cout << circle;
    
    cylinder.shap_name ();
    cout << cylinder;
    
    Shape *pt;
    pt = &point;
    point.get_point () ;
//    pt->get_point (); //用指针调用函数为何不行？！Point是Shape的派生类，指针虽然指向的是Shape类，但是get_point ()声明的是虚函数，应该能用指针调用啊？！！
    cout << "The area of the point is:" << endl;
    pt->area ();
    
    pt = &circle;
    pt->shape_name ();
//    cout << '(' << pt->point_x << ',' << pt->point_y << ')' << endl;
    circle.get_point ();
    cout << "radius = " << circle.get_radius ();
    cout << "The area of the circle is:" << endl;
    cout << circle.area () << endl;
//    cout << pt->area () << endl;
    
    pt = &cylinder;
    pt->shape_name ();
    cylinder.get_point ();
//    cout << '(' << cylinder.point_x << ',' << cylinder.point_y << ')' << endl;
    cylinder.get_radius ();
//    cout << "radius = " << pt->get_radius () << endl;
    cout << "height = ";
    cylinder.get_height ();
//    pt->get_height ();
    cout << "The area of the cylinder is:" << endl;
//    cylinder.volum ();
    cout << pt ->volum ();
}
  

[帅得不敢出门]

//#define pi 3.1415926
double const pi = 3.1415926;

class Shape
{
public:
Shape () {}
virtual double area () const
{
return (0.0);
}
virtual double volum () const
{
return (0.0);
}
virtual void shape_name () const = 0;
//你这里并不 virtual get_point函数的声明 所以下面指向调用get_point就有问题
};

Shape *pt;
pt = &point;
point.get_point () ;
// pt->get_point (); pt指向的虚函数表中并无get_point的函数地址 所以不行

//保护成员在派生类中可以被引用，而私有成员则不能！
这个复习下继承机制
公有继承的特点是基类的公有成员和保护成员作为派生类的成员时，它们都保持原有的状态，而基类的私有成员仍然是私有的。

[蜥蜴枪王]

hehe 每天晚上来小逛一下csdn 收获不小 o(∩_∩)o...
话说，LZ得代码太长了，困了，先帮顶下，明天来瞄瞄=。=

[allen1981813]

楼主你想干嘛？

[leo315]

好长的代码。

[konhon]

Shape裡好像沒get_point的聲明喲.

[reallaoyao]

虚函数调用过程：1，把Point的对象地址取出
2，取出对象开头的指针变量中的地址，此即为VPTR的值
3，调用虚函数

照这样的话，pt->get_point ()是可以调用的，奥妙在哪儿，期待高手回答