第44课 继承中的访问级别

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

class Object
{
protected:        //以下两个成员变量须被子类直接访问
    string mName;
    string mInfo;
public:
    Object()
    {
        mName = "Object";
        mInfo = "";
    }
    
    string name(){return mName;}
    string info(){return mInfo;}
};

class Point : public Object
{
private:    //没有子类，无须被访问
    int mX;
    int mY; 
public:
    Point(int x = 0, int y = 0)
    {
        ostringstream s;
        
        mX = x;
        mY = y;
        mName = "Point";
        
        s << "P(" << mX << ", " << mY << ")";
        
        mInfo = s.str();
    }
    
    int x() {return mX;}
    int y() {return mY;}        
};

class Line : public Object
{
private: 
    Point mP1;
    Point mP2; 
public:
    Line(Point p1, Point p2)
    {
        ostringstream s;
        
        mP1= p1;
        mP2 = p2;
        mName = "Line";
        
        s << "Line from " << mP1.info() << " to " << mP2.info();
        
        mInfo = s.str();
    } 

    Point begin()
    {
        return mP1;
    }
    Point end()
    {
        return mP2;
    }    
};

int main()
{
    Object o;
    Point pb(1, 2);
    Point pe(5, 6);
    Line l(pb, pe);
    
    cout << o.name() << endl;
    cout << o.info() << endl;
    
    cout << endl;
    
    cout << pb.name() << endl;
    cout << pb.info() << endl;
    
    cout << endl;
    
    cout << l.name() << endl;
    cout << l.info() << endl;
      
    return 0;
}