C++ explicit constructor/copy constructor note

C++:explict 作用显示声明构造函数只能被显示调用从而阻止编译器的隐式转换,类似只能用()显示调用，而不能=或者隐式调用

 1 #include <iostream>
 2 #include <vector>
 3 #include <string>
 4 #include <thread>
 5 
 6 class Demo
 7 {
 8 private:
 9     int a;
10 public:
11     explicit Demo()
12             : a(200)
13     {
14         std::cout << "默认构造函数" << std::endl;
15     }
16 
17     ~Demo()
18     {
19         std::cout<<"析构函数"<<std::endl;
20     }
21 
22     explicit Demo(const Demo &other)
23     {
24         a = other.a;
25         std::cout << "拷贝构造函数" << std::endl;
26     }
27 
28     Demo &operator=(const Demo &other)
29     {
30         if (&other == this)
31             return *this;
32         a = other.a;
33         std::cout << "拷贝赋值构造函数" << std::endl;
34         return *this;
35     }
36     
37 };
38 
39 
40 void test(Demo& T)
41 {
42 
43 }
44 
45 
46 int main()
47 {
48     Demo c;            //explicit constructor;
49     Demo D(c);          //explicit copy constructor
50     
51     //test(D)        //this is implicit,error;
52     
53     return 0;
54 }