Efficiency difference between copy and move constructor

Question

C++11 introduced a new concept of rvalue reference. I was reading it somewhere and found following:

class Base
{
public:
    Base()  //Default Ctor
    Base(int          


        

Answer 1

First on your "understandings":

As I can see it, they are in principle right but you should be aware of Copy elision which could prevent the program from calling any copy/move Constructor. Depends on your compiler (-settings).

On your Questions:

1. Yes you have to call foo(std::move(b)) to call an Function which takes an rvalue with an lvalue. std::move will do the cast. Note: std::move itself does not move anything.

2. Using the move-constructor "might" be more efficient. In truth it only enables programmers to implement some more efficient Constructors. Example consider a vector which is a Class around a pointer to an array which holds the data (similar to std::vector), if you copy it you have to copy the data, if you move it you can just pass the pointer and set the old one to nullptr. But as I read in Effective Modern C++ by Scott Meyers: Do not think your program will be faster only because you use std::move everywere.

3. That depends on the usage of the input. If you do not need a copy in the function it will in the most cases be more efficient to just pass the object by (const) reference. If you need a copy there are several ways of doing it for example the copy and swap idiom. But as a