C++ move 复制构造函数和 move 赋值运算符

Question

我用 move 复制构造函数和 move 复制赋值运算符创建了一个简单的应用程序，并且在它们中的每一个上我都做了一个 cout 语句来告诉我，它们正在执行。但是在执行过程中，我没有看到 move 复制运算符的任何语句，而只看到编译器已经提供的默认语句。这是我的代码:

#include <iostream>
#include <string>
using namespace std;

class Names{
private:
    string* name;
public:
    Names(string place_name){
        cout << "Overloaded constructor" << endl;
        name = new string;
        *name = place_name;
    }
    //copy constructor
    Names(Names& cpy){
        cout << "Copy constructor" << endl;
        name = new string;
        *name = *cpy.name;
    }
    //assignment 
    Names& operator =(const Names& cpy){
        cout << "Assignment operator" << endl;
        name = new string;
        *name = *cpy.name;
        return *this;
    }
    //move constructor
    Names(Names&& cpym){
        cout << "Copy move constructor" << endl;
        name = cpym.name;
        cpym.name = NULL;
    }
    //move assignment operator
    Names& operator=(Names&& cpym){
        cout << "Copy assignment operator" << endl;
        delete name;
        name = cpym.name;
        cpym.name = NULL;
        return *this;
    }
    //destructor
    ~Names(){
        cout << "Deallocating memory" << endl;
        delete [] name;
    }
};

int main(){
    Names nme("Bob");
    Names copin("something");
    copin = nme;
    system("pause");
    return 0;
} 

这是输出

所以主要的问题是

1) Why isn't the cout statement being show for the move constructor?
2) Is my declaration for move constructor correct

谢谢你。

Answer 1

move 构造函数和 move 赋值运算符需要使用 std::move 才能工作。请参阅下面我的主要功能:

Names A(Names name) {
    return name;
}
int main(){
    Names nme("Bob");
    Names copin("something");
    cout << "before std::move(nme);" << endl;
    copin = std::move(nme);
    cout << "before std::move(GetName());" << endl;
    Names tom = std::move(nme);
    cout << "before A(Names(\"dick\");" << endl;
    // move constructor is also called when using temp rvalue
    Names dick = A(Names("dick"));
    system("pause");
    return 0;
}

输出:

Overloaded constructor
Overloaded constructor
before std::move(nme);
Copy assignment operator
before std::move(GetName());
Copy move constructor
before A(Names("dick");
Overloaded constructor
Copy move constructor
Copy constructor
Deallocating memory
Deallocating memory
Press any key to continue . . .

还有一个问题，你的析构函数不应该删除[] name，只删除name；