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C++ - Standard library - move
The move template function allows to change an object owner.
We're not going to dive in the heart of the move semantics.
Instead we're going to see a really easy example of how it works.
Let's get started.
First of all
In this move tutorial we're going to create 3 Ships, check their memory address then pass them to a Manager in order to add them to the Manager list.
And each time, we change the scope from a method to another one, the current owner of a ship will transfer the object to another one in a new method or a list.
So the memory address, of the current owner, will be lost after each transfer to the new owner.
The last owner will be the Manager list.
Code
main.cpp
#include <iostream>
#include <string>
#include <list>
#include <memory>
// Badprog.com
class Ship;
// Manager
class Manager {
public:
/**
* CTOR
* */
Manager() {
std::cout << __FUNCTION__ << std::endl;
}
/**
* DTOR
* */
virtual ~Manager() {
std::cout << __FUNCTION__ << std::endl;
}
/**
* addToList
* */
void addToList(std::unique_ptr<Ship> ship) {
std::cout << "ship " << ship.get() << std::endl;
_listShip.push_back(std::move(ship));
std::cout << "ship " << ship.get() << std::endl;
}
/**
* displayWhatThereIsInTheList
* */
void displayWhatThereIsInTheList() {
std::list<std::unique_ptr<Ship>>::iterator iterator;
iterator = _listShip.begin();
while (iterator != _listShip.end()) {
std::cout << "ship: " << iterator->get() << std::endl;
++iterator;
}
}
private:
std::list<std::unique_ptr<Ship>> _listShip;
};
// Ship
class Ship {
public:
/**
* CTOR
* */
Ship(const std::string& name) : _name(name) {
std::cout << __FUNCTION__ << " with name " << _name << std::endl;
}
/**
* DTOR
* */
virtual ~Ship() {
std::cout << __FUNCTION__ << " byebye I was the " << _name << std::endl;
}
private:
std::string _name;
};
/**
* Main
* */
int main() {
auto ship1 = std::make_unique<Ship>("ShipTiny");
auto ship2 = std::make_unique<Ship>("ShipNormal");
auto ship3 = std::make_unique<Ship>("ShipEnormous");
Manager manager;
std::cout << "ship1 " << ship1.get() << std::endl;
std::cout << "ship2 " << ship2.get() << std::endl;
std::cout << "ship3 " << ship3.get() << std::endl;
manager.addToList(std::move(ship1));
manager.addToList(std::move(ship2));
manager.addToList(std::move(ship3));
std::cout << "ship1 " << ship1.get() << std::endl;
std::cout << "ship2 " << ship2.get() << std::endl;
std::cout << "ship3 " << ship3.get() << std::endl;
manager.displayWhatThereIsInTheList();
}
Compiling, linking and running
g++ main.cpp -o go.exe -std=c++1y ; ./go.exe
Result
Ship::Ship with name ShipTiny Ship::Ship with name ShipNormal Ship::Ship with name ShipEnormous Manager::Manager ship1 02FF9988 ship2 02FF4A70 ship3 02FFED40 ship 02FF9988 ship 00000000 ship 02FF4A70 ship 00000000 ship 02FFED40 ship 00000000 ship1 00000000 ship2 00000000 ship3 00000000 ship: 02FF9988 ship: 02FF4A70 ship: 02FFED40 Manager::~Manager Ship::~Ship byebye I was the ShipTiny Ship::~Ship byebye I was the ShipNormal Ship::~Ship byebye I was the ShipEnormous
Conclusion
As expected, each time the owner changes, we can see the memory address transforms to zero.
It isn't just a copy but a complete transfer.
Well done, you got it. 
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