基类与派生类

最新推荐文章于 2023-06-08 23:07:20 发布

原创最新推荐文章于 2023-06-08 23:07:20 发布 · 777 阅读

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#include <iostream>
using std::cout;
using std::endl;
const static double PI =3.1415926;

class Point
{
public:
   Point(float x1 = 0, float y1 = 0,float z1 = 0)
          : x(x1), y(y1), z(z1)
   {}
   float getX() const
   { return x; }
   float getY() const
   { return y; }
    float getZ() const
   { return z;}
protected:
   float x;
   float y;
   float z;
};
class Circle : public Point
{
public:
   Circle( float r = 0,float x = 0, float y = 0 ,float z = 0 );
    float getZ() const
   { return z;}
   float area ( ) const { return PI*PI*radius; }
//protected:
   float radius;
   float y;
    float z;
};
Circle::Circle( float r,float x, float y,float z ) : radius(r)
{
   this->x = x; this->y = y; this->z = z; // 子类没有的,就调用父类的
}
class Car
{
};
void main()
{
    Point *p, pt(11,22,33);
    Circle *pc, pr(10,77,88,99 );
   cout << "derive class' X =" << pr.getX()
       <<" :Y =" << pr.getY()
       <<" :Z ="<< pr.getZ() << endl; // 77,0
   cout << " derive y,z" << pr.y << ":" <<pr.z << endl;
    //把派生类Circle对象的地址赋给了基类指针p
   p = & pr; // 77,0
   cout << "base class' X =" << p ->getX()
       << " :Y ="<< p->getY()
       << " :z ="<< p->getZ() << endl;
   cout << "area = " << pr.area() << endl;

   //cout << "area = " << p->area() << endl;//“area”: 不是“Point”的成员
   //cout << "" << p->
   // p->area(); // error
   // 基类到派生类
   // pc = &pt; // error 无法从“Point *”转换为“Circle *”
   // 原因：基类并不知道自己是否有派生类，它不知道他内存的后面是不是派生类对象
   //       而派生类->基类时，因为派生类必须先构造基类，它知道基类一定存在(?抽象类)
   //把基类指针强制转换为派生类指针
    pc = (Circle *) p;
   cout <<"把基类指针强制转换为派生类指针" << pc->area() << endl;
    p = &pt;
   pc = (Circle *) p;
   cout << "把基类指针强制转换为派生类指针" << pc->area() << endl;
   //cout << pc->radius << endl; //
   // 派生指针转化为基指针
   Car * car;
   pc =(Circle *) car;
   //cout << pc->area() << endl;
}

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程序进行结果

derive class' X =77 :Y =0 :Z =99

derive y,z88:99

base class' X =77 :Y =0 :z =0

area = 98.696

把基类指针强制转换为派生类指针98.696

把基类指针强制转换为派生类指针5.87419e-038