1. C++ Object-Oriented Programming
Templates
Deep copy
Deep delete
September 26, 2017
Cinda Heeren / Geoffrey Tien

2. Cinda Heeren / Geoffrey Tien
PA1 LinkedList
In PA1, you are asked to implement a linked list whose nodes store Kebab pointers
class LinkedList {
private:
class Node {
... };
public:
LinkedList();
void insertFront(Kebab* item);
Kebab* removeAt(unsigned int p);
class Node {
public:
Kebab* data;
Node* next;
Node(Kebab* value); };
Note the Node's data type, function parameter and return types
For PA1, this is fine
September 26, 2017
Cinda Heeren / Geoffrey Tien

3. Linked list of integers
Suppose later I asked you to make a linked list that works with integers
class LinkedList {
private:
class Node {
... };
public:
LinkedList();
void insertFront(Kebab* item);
Kebab* removeAt(unsigned int p);
class Node {
public:
Kebab* data;
Node* next;
Node(Kebab* value); };
int
int
int
And change the implementations accordingly to operate with integers
int
This is fine too, for now...
September 26, 2017
Cinda Heeren / Geoffrey Tien

4. Different linked lists
Now I ask you to write a program that keeps a list of Kebab pointers, and also a list of the size of each Kebab
class LinkedList {
private:
class Node {
... };
public:
LinkedList();
void insertFront(Kebab* item);
Kebab* removeAt(unsigned int p);
LinkedListKP
class LinkedList {
private:
class Node {
... };
public:
LinkedList();
void insertFront(int item);
int removeAt(unsigned int p);
LinkedListInt
LinkedListKP
LinkedListInt
A lot of redundancy, but it will work...
September 26, 2017
Cinda Heeren / Geoffrey Tien

5. Something for everyone
and then I ask you to write a linked list to support strings, and another to store doubles
copy/paste into two new classes?
...and then I ask you to add a new function, findMax()
need to paste into every linked list implementation
Geoff's evaluations go way down
September 26, 2017
Cinda Heeren / Geoffrey Tien

6. Cinda Heeren / Geoffrey Tien
Templates
Template classes allow the separation of the functionality of a class, from the type of data used in the class
Without templates, the programmer must know beforehand what type of data will be used
and then write the functionality to support the data type
With templates, the programmer writes the functionality to work with some generic data type
the actual data type is determined when the object is created
September 26, 2017
Cinda Heeren / Geoffrey Tien

7. Declaring template classes
.h file
Class definition, data fields, parameters, return values
class LinkedList {
private:
class Node {
public:
int data;
Node* next;
... };
LinkedList();
void insertFront(int item);
int removeAt(unsigned int p);
template <typename ItemType>
class LinkedList {
private:
class Node {
public:
ItemType data;
Node* next;
... };
LinkedList();
void insertFront(ItemType item);
ItemType removeAt(unsigned int p);
September 26, 2017
Cinda Heeren / Geoffrey Tien

8. Implementing template class functions
.cpp file
// return the item at the
// front of the list
int LinkedList::getFront() {
return front->data; }
// return the item at the
// front of the list
template <typename ItemType>
ItemType LinkedList<ItemType>::getFront() {
return front->data; }
Node functions will also need to be templated
September 26, 2017
Cinda Heeren / Geoffrey Tien

9. Linking template classes
// Header file
#ifndef _LINKEDLIST_H_
#define _LINKEDLIST_H_
template <typename ItemType>
class LinkedList {
... };
#include "linkedlist.cpp"
#endif
// Implementation file
#include "linkedlist.h"
// Default constructor
template <typename ItemType>
LinkedList<ItemType>::LinkedList {
... }
#ifdef _LINKEDLIST_H_
// #include "linkedlist.h"
#endif
September 26, 2017
Cinda Heeren / Geoffrey Tien

10. Using template classes
Template class objects are instantiated with the type specified within <angle brackets>
LinkedList<double> my_doubles;
my_doubles.insertBack(0.380);
LinkedList<string>* my_strings = new LinkedList<string>();
my_strings->insertBack("I learned to use templates today");
vector is a template class which you have used already!
vector<char> skewer;
skewer.push_back('B');
vector<string> Grill::showKebabs() {
... }
September 26, 2017
Cinda Heeren / Geoffrey Tien

11. Cinda Heeren / Geoffrey Tien
Deep copy / deep delete
September 26, 2017
Cinda Heeren / Geoffrey Tien

12. Passing objects by value
When objects are passed by value as function parameters, a copy of the object must be placed on the call stack
we need a way to copy the object members
Without explicitly implementing a copy constructor, a shallow copy occurs by default
only the values of fields are copied
this may cause problems if the object contains members in dynamic memory
September 26, 2017
Cinda Heeren / Geoffrey Tien

13. Cinda Heeren / Geoffrey Tien
Shallow copy
stack
heap
LinkedList lla;
...
lla
length
front
back 3 3 5 7
LinkedList llb(lla);
llb.removeFront();
llb
length
front
back !!
lla.elementAt(1); 3 2
September 26, 2017
Cinda Heeren / Geoffrey Tien

14. Cinda Heeren / Geoffrey Tien
Deep copy
A deep copy creates new values in dynamic memory, containing values equivalent to the original
this must be explicitly programmed
stack
heap
LinkedList lla;
...
lla
length
front
back 3 3 5 7
LinkedList llb(lla);
llb.removeFront();
llb
length
front
back
lla.elementAt(1); 2 3 3 5 7
September 26, 2017
Cinda Heeren / Geoffrey Tien

15. Cinda Heeren / Geoffrey Tien
Destroying objects
When an object goes out of scope, any stack memory associated with the object is released automatically
but if the object has members in dynamic memory, it will leak!
stack
heap
void f1() {
LinkedList lla;
... }
lla
length
front
back 3 3 5 7
memory leak!
September 26, 2017
Cinda Heeren / Geoffrey Tien

16. Cinda Heeren / Geoffrey Tien
Deep delete
A destructor allows programmer to explicitly define additional steps to be taken when an object is destroyed
deallocate dynamic members with delete
stack
heap
void f1() {
LinkedList lla;
... }
lla
length
front
back 3 3 5 7
all memory released
September 26, 2017
Cinda Heeren / Geoffrey Tien

17. Assignment
It might require both deep delete and deep copy!
By default, objects are given an = operator which performs a shallow copy of all fields
again, if an object has dynamic members, we want to deep copy
but, if there are existing data in dynamic memory before assignment, it must be deallocated
stack
heap
lla
length
front
back 3
LinkedList lla;
...
LinkedList llb; 3 5 7 6 2
llb = lla;
llb
length
front
back 3 2 3 5 7
September 26, 2017
Cinda Heeren / Geoffrey Tien

18. Readings for this lesson
Koffman
Chapter 1.3, 4.1, 4.4
Next class:
Koffman Chapter 1.4, 5
September 26, 2017
Cinda Heeren / Geoffrey Tien