C++ 类的聚集和浅拷贝与深拷贝

1.类的聚集

类的成员中含有某类的指针，这种类叫类的聚集。又被称为“远程所有权”（remote ownership）。

该类的对象的数据将存放在对象外边，对象中只存放数据的地址。数据可以是数组、对象等。

2.浅拷贝与深拷贝

浅拷贝

–实现对象间数据元素的一一对应复制。这是拷贝构造函数的本能。当数据元素是指针的时候，则出问题。

深拷贝

–当被复制的对象数据成员是指针类型时，不是复制该指针成员本身，而是将指针所指的对象（区域）进行复制。

对象的浅拷贝

//对象的浅拷贝#include<iostream>using namespace std;class Point{ public:Point(){ X=Y=0; cout<<"Default Constructor called.\n";}Point(int xx,int yy){ X=xx; Y=yy; cout<< "Constructor called.\n"; }~Point() { cout<<"Destructor called.\n"; }int GetX() {return X;}int GetY() {return Y;}void Move(int x,int y){ X=x; Y=y; }private:int X,Y;};class ArrayOfPoints     //这个类叫“控制类”{ public:ArrayOfPoints(int n) // 按照指示创建指定个数的对象{ numberOfPoints = n;points = new Point[n]; }~ArrayOfPoints(){ cout<<"Deleting..."<<endl;numberOfPoints=0; delete[] points; }Point& Element(int n){ return points[n]; }private:Point *points; //类内只保存对象数组的首址int numberOfPoints; //对象的个数};void main(){int number;cout << "Please enter the number of points:";cin>>number;ArrayOfPoints pointsArray1(number); pointsArray1.Element(0).Move(5,10); pointsArray1.Element(1).Move(15,20);//对象的浅拷贝ArrayOfPoints pointsArray2(pointsArray1);//输出对象的值cout<<"Copy of pointsArray1:"<<endl;cout<<"Point_0 of array2: "<<pointsArray2.Element(0).GetX()<<", "<<pointsArray2.Element(0).GetY()<<endl;cout<<"Point_1 of array2: "<<pointsArray2.Element(1).GetX()<<", "<<pointsArray2.Element(1).GetY()<<endl;//对象1的值改变同时也会改变对象2的值pointsArray1.Element(0).Move(25,30);pointsArray1.Element(1).Move(35,40);//输出对象的值cout<<"After the moving of pointsArray1:"<<endl;cout<<"Point_0 of array2: "<<pointsArray2.Element(0).GetX()<<", "<<pointsArray2.Element(0).GetY()<<endl;cout<<"Point_1 of array2: "<<pointsArray2.Element(1).GetX()<<", "<<pointsArray2.Element(1).GetY()<<endl;}

运行结果：

Please enter the number of points:2
Default Constructor called.
Default Constructor called.
Copy of pointsArray1:
Point_0 of array2: 5, 10
Point_1 of array2: 15, 20
After the moving of pointsArray1:
Point_0 of array2: 25, 30
Point_1 of array2: 35, 40
Deleting...
Destructor called.
Destructor called.
Deleting...（同一块空间被释放了两次）

接下来程序出现异常，也就是运行错误。

对象的深拷贝

//对象的深拷贝#include<iostream>using namespace std;class Point{ public:Point(){ X=Y=0; cout<<"Default Constructor called.\n";}Point(int xx,int yy){ X=xx; Y=yy; cout<< "Constructor called.\n"; }~Point() { cout<<"Destructor called.\n"; }int GetX() {return X;}int GetY() {return Y;}void Move(int x,int y){ X=x; Y=y; }private:int X,Y;};class ArrayOfPoints     //这个类叫“控制类”{ public:ArrayOfPoints(int n) // 按照指示创建指定个数的对象{ numberOfPoints = n;points = new Point[n]; }//不能用默认的拷贝构造函数，必须重写了ArrayOfPoints(ArrayOfPoints& pointsArray);~ArrayOfPoints(){ cout<<"Deleting..."<<endl;numberOfPoints=0; delete[] points; }Point& Element(int n){ return points[n]; }private:Point *points; //类内只保存对象数组的首址int numberOfPoints; //对象的个数};//拷贝构造函数ArrayOfPoints::ArrayOfPoints(ArrayOfPoints& pointsArray){ numberOfPoints = pointsArray.numberOfPoints;//申请新的空间points=new Point[numberOfPoints];for (int i=0; i<numberOfPoints; i++)//把值拷贝过来points[i].Move(pointsArray.Element(i).GetX(),pointsArray.Element(i).GetY());}void main(){int number;cout << "Please enter the number of points:";cin>>number;ArrayOfPoints pointsArray1(number); pointsArray1.Element(0).Move(5,10); pointsArray1.Element(1).Move(15,20);cout << "test\n";//对象的深拷贝ArrayOfPoints pointsArray2(pointsArray1);cout<<"Copy of pointsArray1:"<<endl;cout<<"Point_0 of array2: "<<pointsArray2.Element(0).GetX()<<", "<<pointsArray2.Element(0).GetY()<<endl;cout<<"Point_1 of array2: "<<pointsArray2.Element(1).GetX()<<", "<<pointsArray2.Element(1).GetY()<<endl;    //深拷贝对象2的值不会因对象1的值改变而改变pointsArray1.Element(0).Move(25,30);pointsArray1.Element(1).Move(35,40);cout<<"After the moving of pointsArray1:"<<endl;cout<<"Point_0 of array2: "<<pointsArray2.Element(0).GetX()<<", "<<pointsArray2.Element(0).GetY()<<endl;cout<<"Point_1 of array2: "<<pointsArray2.Element(1).GetX()<<", "<<pointsArray2.Element(1).GetY()<<endl;}

运行结果：

Please enter the number of points:2
Default Constructor called.
Default Constructor called.
Default Constructor called.
Default Constructor called.
Copy of pointsArray1:
Point_0 of array2: 5, 10
Point_1 of array2: 15, 20
After the moving of pointsArray1:
Point_0 of array2: 5, 10
Point_1 of array2: 15, 20
Deleting...
Destructor called.
Destructor called.
Deleting...
Destructor called.
Destructor called.
Press any key to continue

使用动态存储分配的类要重写拷贝构造函数！