C++中对象的深层复制

我不是女神ヾ 2022-02-24 18:34 190阅读 0赞

**深层复制与浅层复制最主要的区别在于：**  
1.浅层复制只是对指针的复制，两个对象中的指针实际上指向同一块内存区域，所以改变其中任意一个的值，都会对另一个产生影响；  
2.深层复制是对元素值的复制，复制构造函数会重新申请一块大小合适的内存空间来存储原来元素的值，所以深层复制后的对象与原对象之间并无关联关系。

/*---------------------------------------
    功能：对象的深层复制
    运行结果：
    Input the number of point: 2
    Calling default constructor of Point...
    Calling default constructor of Point...
    Calling constructor of ArrayPoint...
    Calling default constructor of Point...
    Calling default constructor of Point...
    The original position of points2:
    (1, 2)
    (3, 4)
    The changed position of points1:
    (5, 6)
    (7, 8)
    The current position of points1:
    (1, 2)
    (3, 4)
    Calling destructor of PointArray...
    Calling destructor of Point...
    Calling destructor of Point...
    Calling destructor of PointArray...
    Calling destructor of Point...
    Calling destructor of Point...
    -----------------------------------------
    Author: Zhang Kaizhou
    Date: 2019-4-4 18:04:03
    ----------------------------------------*/
    #include <iostream>
    #include <cassert>
    
    using namespace std;
    
    class Point{ // 创建一个点Point类
    private:
        int x, y;
    public:
        Point(){ cout << "Calling default constructor of Point..." << endl; } // 默认构造函数
        Point(int xx, int yy):x(xx), y(yy){ cout << "Calling parameter constructor of Point..." << endl; } // 含参构造函数
        Point(Point & p){ // 复制构造函数
            x = p.x;
            y = p.y;
        }
        ~Point(){ cout << "Calling destructor of Point..." << endl; } // 析构函数
        void showPos(){ cout << "(" << x << ", " << y << ")" << endl; }
        void movePos(int xx, int yy){ x = xx; y = yy; }
    };
    
    class PointArray{ // 创建PointArray类
    private:
        Point * points; // 指向动态数组首地址的指针
        int len; // 数组长度
    public:
        PointArray(int len):len(len){ points = new Point[len]; cout << "Calling constructor of ArrayPoint..." << endl; } // 构造函数，利用new关键字动态创建len长度的数组
        PointArray(const PointArray & pA){ // 复制构造函数，实现深层复制
            len = pA.len;
            points = new Point[len];
            for(int i = 0; i < len; i++){
                points[i] = pA.points[i];
            }
        }
        ~PointArray(){ cout << "Calling destructor of PointArray..." << endl; delete [] points; } // 析构函数
        Point & element(int index){ // 该函数的返回值是一个Point类的对象的引用
            assert(index >= 0 && index < len); // assert断言语句，若条件为假，则打印错误信息，并终止程序
            return points[index];
        }
    };
    
    int main(){
        int pointCount;
        cout << "Input the number of point: ";
        cin >> pointCount; // 点总数
        PointArray points1(pointCount); // 创建一个点数组对象points，点的总数为pointCount
        points1.element(0).movePos(1, 2);
        points1.element(1).movePos(3, 4);
    
        PointArray points2(points1); // 调用复制构造函数实现深层复制
        cout << "The original position of points2:" << endl;
        points2.element(0).showPos();
        points2.element(1).showPos();
    
        points1.element(0).movePos(5, 6); // 改变points1中点的位置
        points1.element(1).movePos(7, 8);
        cout << "The changed position of points1:" << endl;
        points1.element(0).showPos();
        points1.element(1).showPos();
        cout << "The current position of points1:" << endl;
        points2.element(0).showPos(); // 改变points中点的位置后，对points2中点的位置没有影响
        points2.element(1).showPos();
    
        return 0;
    }