何时需要自定义拷贝构造函数

 1 #include<iostream>
 2 
 3 class A
 4 {
 5     public:
 6         A() 
 7         {   
 8             std::cout << "constructor is called" << std::endl;
 9             n = new int[10];
10             n[0] = 1;
11         }
12         // 默认拷贝构造函数
13         /*A(const A &t)
14         {
15             std::cout << "copy constructor is called" << std::endl;
16             n = t.n;
17         }
18         */
19 
20         ~A()
21         {   
22             std::cout << "destructor is called" << std::endl;
23             delete n;
24         }   
25 
26         void get() { std::cout << "n[0]: " << n[0] << std::endl; }
27     private:
28         int *n; 
29 };
30 
31 int main(void)
32 {
33     A a;
34     A b(a);
35     b.get();
36 
37     return 0;
38 }

 1 #include<iostream>
 2 #include<string.h>
 3 
 4 class A
 5 {
 6     public:
 7         A() 
 8         {   
 9             std::cout << "constructor is called" << std::endl;
10             n = new int[10];
11             n[0] = 1;
12         }   
13         // 深拷贝
14         A(const A &t) 
15         {   
16             std::cout << "copy constructor is called" << std::endl;
17             n = new int[10];
18             memcpy(n, t.n, 10);
19         }   
20 
21         ~A()
22         {   
23             std::cout << "destructor is called" << std::endl;
24             delete n;
25         }   
26 
27         void get() { std::cout << "n[0]: " << n[0] << std::endl; }
28     private:
29         int *n; 
30 };
31 
32 int main(void)
33 {
34     A a;
35     A b(a);
36     b.get();
37 
38     return 0;
39 }