复制构造函数——深复制 浅复制

隐含的复制构造函数并不总是适用的，因为它完成的只是浅复制。

对象的浅复制

 1 #include<iostream>
 2 #include<cassert>
 3 using namespace std;
 4 class Point{
 5 public:
 6     Point() :x(0), y(0)//默认构造函数
 7     {
 8         cout << "constructor1" << endl;
 9     }
10     Point(int x, int y) :x(x), y(y)
11     {
12         cout << "constructor2" << endl;
13     }
14     ~Point()
15     {
16         cout << "destructor" << endl;
17     }
18     int getX()
19     {
20         return x;
21     }
22     int getY()
23     {
24         return y;
25     }
26     void move(int mx, int my)
27     {
28         x += mx;
29         y += my;
30     }
31 private:
32     int x, y;
33 };
34
35 class PointArray{
36 public:
37     PointArray(int size) :size(size)
38     {
39         ptr = new Point[size];
40     }
41
42     ~PointArray()
43     {
44         cout << "析构" << endl;
45         delete[] ptr;
46     }
47
48     Point &getElement(int index)
49     {
50         assert(index >= 0 && index < size);//如果数组下标越界，程序终止
51         return ptr[index];
52     }
53
54 private:
55     Point *ptr;
56     int size;
57 };
58
59 int main()
60 {
61     int size;
62     cout << "请输入size的值：";
63     cin >> size;
64
65     PointArray pointArray1(size);
66     pointArray1.getElement(0).move(1, 1);
67     pointArray1.getElement(1).move(3, 3);
68
69     PointArray pointArray2 = pointArray1;
70     cout << pointArray2.getElement(0).getX() << "," << pointArray2.getElement(0).getY() << endl;
71     cout << pointArray2.getElement(1).getX() << "," << pointArray2.getElement(1).getY() << endl;
72
73     pointArray1.getElement(0).move(7, 7);
74     pointArray1.getElement(1).move(11, 11);
75     cout << pointArray2.getElement(0).getX() << "," << pointArray2.getElement(0).getY() << endl;
76     cout << pointArray2.getElement(1).getX() << "," << pointArray2.getElement(1).getY() << endl;
77
78     return 0;
79 }

pointArray1和pointArray2的成员ptr指向的是同一内存地址，表面上好像完成了复制，但是并没有形成真正的副本。因此当程序移动pointArray1中的点时，也影响到了pointArray2。这种效果就是浅复制。

浅复制还有更大的弊病：程序结束前，pointArray1和pointArray2的析构函数会自动被调用，动态内存空间会被释放。由于两个对象共用同一块内存空间，因此该空间被两次释放，于是导致运行错误。

对象的深复制

 1 #include<iostream>
 2 #include<cassert>
 3 using namespace std;
 4
 5 class Point{
 6 public:
 7     Point() :x(0), y(0)//默认构造函数
 8     {
 9         cout << "constructor1" << endl;
10     }
11     Point(int x, int y) :x(x), y(y)
12     {
13         cout << "constructor2" << endl;
14     }
15     ~Point()
16     {
17         cout << "destructor" << endl;
18     }
19     int getX()
20     {
21         return x;
22     }
23     int getY()
24     {
25         return y;
26     }
27     void move(int mx, int my)
28     {
29         x += mx;
30         y += my;
31     }
32 private:
33     int x, y;
34 };
35
36 class PointArray{
37 public:
38     PointArray(int size) :size(size)
39     {
40         ptr = new Point[size];
41     }
42
43     PointArray(const PointArray &pArray)
44     {
45         size = pArray.size;
46         ptr = new Point[size];
47         for (int i = 0; i < size; i++)
48         {
49             ptr[i] = pArray.ptr[i];
50         }
51     }
52
53     ~PointArray()
54     {
55         cout << "析构" << endl;
56         delete[] ptr;
57     }
58
59     Point &getElement(int index)
60     {
61         assert(index >= 0 && index < size);//如果数组下标越界，程序终止
62         return ptr[index];
63     }
64
65 private:
66     Point *ptr;
67     int size;
68 };
69
70 int main()
71 {
72     int size;
73     cout << "请输入size的值：";
74     cin >> size;
75
76     PointArray pointArray1(size);
77     pointArray1.getElement(0).move(1, 1);
78     pointArray1.getElement(1).move(3, 3);
79
80     PointArray pointArray2 = pointArray1;
81     cout << pointArray2.getElement(0).getX() << "," << pointArray2.getElement(0).getY() << endl;
82     cout << pointArray2.getElement(1).getX() << "," << pointArray2.getElement(1).getY() << endl;
83
84     pointArray1.getElement(0).move(7, 7);
85     pointArray1.getElement(1).move(11, 11);
86     cout << pointArray2.getElement(0).getX() << "," << pointArray2.getElement(0).getY() << endl;
87     cout << pointArray2.getElement(1).getX() << "," << pointArray2.getElement(1).getY() << endl;
88
89     return 0;
90 }

　　移动pointArray1中的点不再影响pointArray2中的点，而且程序结束前分别释放内存空间。