Temporary variables and copy constructors

Class B{public:b () {cout << constructors << Endl;} B (const b &b) {cout << copy constructor << Endl;} ~b () {cout << "destructor" << Endl;}}; b Play (b b) {return B;}

The main function enters the following code:

{B B1;play (B1);}

Output:

The main function enters the following code:

{B B1; B B2=play (B1);}

Output:

Why are the two graphs the same? I guess it's because B B2=play (B1); This line of code produces a temporary return value variable by copying the constructor, and then B2 calls the move copy constructor?

To do the experiment, add the assignment operator and the move constructor:

<pre name= "code" class= "CPP" >class b{public:b () {cout << "constructors" << Endl;} B (const b &b) {cout << copy constructor << Endl;} B (b &&b) {cout << move constructor << Endl;} b& operator= (const B &b) {cout << assignment operator << endl;if (this = = &b) return *this;return *this;} ~b () {cout << "destructor" << Endl;}}; b Play (b b) {return B;} void Main () {{B B1; B B2 = Play (B1);} cout << "-------------------------" << Endl; {B B1; B b2;b2 = Play (B1);}}

Output:

Remove the Move constructor:

Class B  {public  :      B () {          cout << "constructors" << Endl;      }      B (const b &b)      {          cout << copy constructor << Endl;      }      b& operator= (const B &b)      {          cout << assignment operator << Endl;          if (this = = &b)              return *this;          return *this;      }            ~b ()      {          cout << "destructor" << Endl;      }  };    b Play (b b)  {      return b;  }    void Main ()  {      {          B B1;          B B2;          B2 = Play (B1);      }  

Output:

Temporary variables and copy constructors