Question

#include <iostream>

using namespace std;

struct A
{
    A() {}
    A(const A &a) {
        cout << "copy constructor" << endl;
    }
    A& operator=(const A &a) {
        cout << "assigment operator" << endl;
    }
    A(A &&a) {
        cout << "move" << endl;
    }
    A& operator=(A &&a) {
        cout << "move" << endl;
    }
};

struct B {
    A a;
};

B func() {
    B b;
    return b;
}
int main() {
    B b = func();
}

This prints “copy constructor”.

For class B the move constructor and the move assignment operator should be automatic generated correct? But why is it using the copy constructor of class A and not the move constructor?

Answer 1

For me it doesn’t print anything at all because the copy/move has been elided. However if I thwart RVO with something like:

extern bool choice;

B func() {
    B b1, b2;
    if (choice)
      return b1;
    return b2;
}

Then it prints:

move

It may be that your compiler does not yet implement the automatic generation of the move members.