C ++ - 按值返回对象

Question

以下是测试按值返回的示例程序

1. 为什么函数本地obj地址和主本地对象具有相同的地址??
2. 为什么在按值返回对象时没有调用构造函数？

3. 为什么在红色对象被析构函数被调用时不会在函数中调用黄色对象析构函数

   class Demo 
   {
   
   string s_name;
   
   public:
   
      Demo() 
          {
   
               cout << s_name << "Default constructor " << endl;
       }
       Demo(string name):s_name(name){
           cout <<  s_name << "  in Demo::Demo(string)" << endl;
       }
       Demo(Demo && p){
           cout << s_name << "  in Demo::Demo( && )" << endl;
           s_name=p.s_name;
   
       }
       Demo(Demo const & p){
           cout << s_name << "  in Demo::Demo( && )" << endl;
       }
   
       ~Demo() {
           cout << s_name << "  in Demo::~Demo()" << endl;
       }
       const string & getname(){ return s_name;};
   };
   
   Demo fun() {
       Demo  a("Red"),b("Yellow");
       cout << b.getname() << " Addres of  in fun     " << &b << endl <<endl;
       return b;
   }
   
   int main() {
   
       Demo   obj = fun();
       cout << endl << obj.getname() <<  " Addres of   in main " << &obj << endl << endl;
   
       return 0;
   }
   

输出

Red  in Demo::Demo(string)
Yellow  in Demo::Demo(string)
Yellow Addres of  in fun     0x7342d7c3b7f0

Red  in Demo::~Demo()

Yellow Addres of   in main 0x7342d7c3b7f0

Yellow  in Demo::~Demo()

1. 正如What are copy elision and return value optimization?中所述：如果这是带有命名的返回值优化 - 那么如果我们使用移动语义返回函数，我们获得的优势是什么

   Demo fun（）{
    演示d;
        return std :: move（d）;
   }