Copy Constructors and Deep vs Shallow Copy in C++, Study notes of Object Oriented Programming

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Copy Constructor

! 1

Copy Constructor

1. Initialize one object from another of the same type

MyClass one; MyClass two = one;

More explicitly

MyClass one; MyClass two(one); // Identical to above.

2. Copy an object to pass by value as an argument to a function

void MyFunction(MyClass arg) { /* ... */ }

3. Copy an object to be returned by a function

MyClass MyFunction() {

MyClass mc;

return mc;

! 2

Creates a new object

as a copy of another one

Compiler will provide one

but may not appropriate

for complex objects

Deep vs Shallow Copy

! 4

Overloaded operator=

MyClass one;

//Stuff here

MyClass two = one;

IS DIFFERENT FROM

MyClass one, two;

//Stuff here

two = one;

! 5 Instantiation: copy constructor is called

Assignment, NOT

instantiation: no constructor

is called, must overload

operator= to avoid

shallow copy

orig_chain_ptr

new_chain_ptr

// Copy first node head_ptr_ = new Node(); head_ptr_->setItem(orig_chain_ptr->getItem()); // Copy remaining nodes Node* new_chain_ptr = head_ptr_; // Points to last node in new chain orig_chain_ptr = orig_chain_ptr->getNext(); Deep vs Shallow Copy

! 8

orig_chain_ptr

new_chain_ptr

Deep vs Shallow Copy // Copy first node head_ptr_ = new Node(); head_ptr_->setItem(orig_chain_ptr->getItem()); // Copy remaining nodes Node* new_chain_ptr = head_ptr_; // Points to last node in new chain orig_chain_ptr = orig_chain_ptr->getNext();

orig_chain_ptr

new_chain_ptr

Deep vs Shallow Copy while (orig_chain_ptr != nullptr) { // Get next item from original chain ItemType next_item = orig_chain_ptr->getItem(); //Create a new node containing the next item Node* new_node_ptr = new Node(next_item); //Link new node to end of new chain new_chain_ptr->setNext(new_node_ptr); // Advance pointer to new last node new_chain_ptr = new_chain_ptr->getNext(); / Advance original-chain pointer orig_chain_ptr = orig_chain_ptr->getNext(); }

orig_chain_ptr

new_chain_ptr

Deep vs Shallow Copy while (orig_chain_ptr != nullptr) { // Get next item from original chain ItemType next_item = orig_chain_ptr->getItem(); //Create a new node containing the next item Node* new_node_ptr = new Node(next_item); //Link new node to end of new chain new_chain_ptr->setNext(new_node_ptr); // Advance pointer to new last node new_chain_ptr = new_chain_ptr->getNext(); / Advance original-chain pointer orig_chain_ptr = orig_chain_ptr->getNext(); }

orig_chain_ptr

new_chain_ptr

Deep vs Shallow Copy while (orig_chain_ptr != nullptr) { // Get next item from original chain ItemType next_item = orig_chain_ptr->getItem(); //Create a new node containing the next item Node* new_node_ptr = new Node(next_item); //Link new node to end of new chain new_chain_ptr->setNext(new_node_ptr); // Advance pointer to new last node new_chain_ptr = new_chain_ptr->getNext(); / Advance original-chain pointer orig_chain_ptr = orig_chain_ptr->getNext(); }

orig_chain_ptr

new_chain_ptr

Deep vs Shallow Copy while (orig_chain_ptr != nullptr) { // Get next item from original chain ItemType next_item = orig_chain_ptr->getItem(); //Create a new node containing the next item Node* new_node_ptr = new Node(next_item); //Link new node to end of new chain new_chain_ptr->setNext(new_node_ptr); // Advance pointer to new last node new_chain_ptr = new_chain_ptr->getNext(); / Advance original-chain pointer orig_chain_ptr = orig_chain_ptr->getNext(); }

! 16

orig_chain_ptr

new_chain_ptr

Deep vs Shallow Copy while (orig_chain_ptr != nullptr) { // Get next item from original chain ItemType next_item = orig_chain_ptr->getItem(); //Create a new node containing the next item Node* new_node_ptr = new Node(next_item); //Link new node to end of new chain new_chain_ptr->setNext(new_node_ptr); // Advance pointer to new last node new_chain_ptr = new_chain_ptr->getNext(); / Advance original-chain pointer orig_chain_ptr = orig_chain_ptr->getNext(); }

Efficiency Considerations

Every time you pass or return an object by value:

- Call copy constructor

- Call destructor

For linked chain:

- Traverse entire chain to copy ( n “ steps ”)

- Traverse entire chain to destroy ( n “ steps ”)

Preferred:

myFunction(const MyClass& object);

! 17