22.C++- 继承与组合,protected访问级别

class Parent
{
       int mValue;
public:    
       Parent()
       {
              mValue=10;
       }  
       int Value()
       {
              return mValue;
       } 
};

class Child : public Parent
{
public:    
        Child()
       {
              cout<<"I'm child"<<endl;
       }
};

int main()
{
       Child c;

       cout<< c.Value() <<endl;   //调用父类的成员函数

       Parent p1 =c;        　　  //通过子类初始化父类

       Parent p2;

       p2=c;                    //通过子类复制给父类
}

class Parent
{
       int mValue;
public:    
       Parent(int i=0)
       {
              mValue=i;
       }
       int Value()
       {
              return mValue;
       } 
};

class Child : public Parent
{
public:    
        Child()
       {
          cout<<mValue<<endl;         //在子类中,访问父类的private成员,将会编译报错
       }
};

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

using namespace std;

class Object
{
protected:
       string mName;
       string mInfo;
public:
        Object()
       {
              mName="Object";
              mInfo="";             
       }
       string name()
       {
              return mName;
       }
       string info()
       {
              return mInfo;
       }
};

class Point      : public Object
{
protected:
       int x;                     //坐标
       int y;

public:
       Point(int x=0,int y=0)
       {
              ostringstream s;
              this->x =x;
              this->y =y;
              s<<"P("<<x<<","<<y<<")";  //坐标信息
              mName="Point";
              mInfo=s.str();
       } 
};

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

int main()
{
       Point p1(2,3); 
       Point p2(6,3);
       Line  L(p1,p2);

       /*打印点的信息*/
       cout<<p1.name()<<":"<<endl;
       cout<<p1.info()<<endl;

       /*打印线的信息*/
       cout<<L.name()<<":"<<endl;
       cout<<L.info()<<endl;
       return 0;
}

Point:
P(2,3)

Line:
Line from P(2,3) to P(6,3)