Rossella Lau Lecture 4, DCO20105, Semester A,2005-6 DCO 20105 Data structures and algorithms Lecture 4: C++ and list Usage of Vector and List C++

Rossella Lau Lecture 4, DCO20105, Semester A,2005-6

DCO20105 Data structures and algorithms

Lecture 4: C++ and list

Usage of Vector and List C++ reference STL’s list and its usage

-- By Rossella Lau


<list> vs <vector> (or array)

Vector (or array) List

Adding/removing elements

fast when appending while there is still room or deleting the last element

fast when adding/deleting an element in any position if the position is set

Accessing can be sorted and accessed by efficient method such as binary search

no random access, should be linear search

Memory allocation/de-allocation

Actions are only required when the array needs to be re-sized

Actions are required for each add/delete operation on a list


Notes on memory allocation

In theory, list is efficient for applications in which storage is variant and insert/remove operations are required

However, memory allocation or de-allocation is a very expensive operation

It involves lots of steps to look for storage, computing positions of occupied or free memory

In the following discussion, we assume that we have an efficient memory allocation method


Application considerations

In bookShop Sales: only append, no update, no search List Catalog: one load, no update, search frequently

Sorted vector with binary search Order: volume is variant, search is frequently

• List: append easily, but can only apply linear search• Vector: ordered or random? may apply binary search

but needs shift operations for “insert”


C++ pointer considerations on list

Indirect identification of a part

Each part of a node must be identified through a node, and usually a pointer: e.g.,

ptritem ptrnext

itemnext

ptr


ptrnext

Consider it in an assignment operation When it is on the left hand side, it is going to be assigned a

value to point to another node• E.g., ptr->next = node2;

changes ptr->next pointing to node2

When it is on the right hand side, it represents the next nodes on the linked list; e.g., ptr=ptrnext changes ptr pointing to node1

itemnext

ptr

itemnext

node2itemnext

node1


C++ reference

Using C++ reference can make an alias for ptr next

It allows for a simpler coding for insert_before() and insert_after() with find()


Reference re-visitTo simplify pointer operation in C, C++ supports

one more form to represent an object: reference

To define a reference; e.g., int & refA = a; or Product & refP = p; where a and p are ordinary variables in a program

A reference must reference to another object and can not reference to null value


Use of reference

A reference internally is an address, same as a pointer, but it can be used as the way of a real object/datum; i.e., it does not require dereferencing; e.g., refA = b; // assign b to a refP.getCode();

It can also give a “name” to a dynamic area: e.g., Node & refNode = * (new Node);


Example of reference

What is the output? int a, b; int & refA = a; Node& aNode = * (new Node); Cin >> b; //input 15 a = 25; refA = b; aNode.item = refA; cout << aNode.item;


Reference of ptr->next

Node * & target = ptrnext;

target = node2;

ptr = target

itemnext

ptr

itemnext

node2itemnext

node1target


Interesting reference

Since a function can return a reference, a function call can be on the left hand side of an assignment:

int & min(int &lhs, &rhs) { return a < b? a : b; } …… int a, b; cin >> a >> b; min(a, b) += 1;


The declaration of Node<T> * & is a reference of a pointer which can name a part of a node; e.g., Node<T> *& target = nodePtr->next;

Since the part can be directly referred, find(), in List.h, allows for the found part to have an alias name

The name itself can be assigned a value, i.e., pointing to another node; i.e., link to another node or linked list

The name itself also represents a value which points to the next node

With find(), insert() can be as easy as:target = new Node<T>( item, target);

Node<T> *& find()itemnext next

targetV


C++ notes on destructor

When designing destructor for friend classes, it should be careful to determine which destructor is responsible for memory de-allocation.

If the de-allocation places the destructor in Node<T>, chain effects may accidentally happen

Because de-allocating a node would cause the destructor of another node (next) to be executed!


STL’s list

It is a doubly linked list

Ford’s slide 6:3

Operations on a doubly linked list: Ford’s slide: 9:12-16

fro nt b ac k


Methods of STL’s list

Method names of different containers in the STL are identical

• push_front(), push_back()• front(), back()• pop_front(), pop_front()• list<T>::iterator is provided (forward/backward only)• list<T>::const_iterator is for traversal on constant objects• size()• Syntax and other methods: Ford: 6: 6-13• Operator overload operations: 6:14

Header file <list> is needed


Sample usage of STL’s listFord’s slide: 6:15 insert()

Ford’s slide 6:16 erase()

Ford’s review exercises: 1,2,5,6,7

fro nt

Lis t o b je c t (a fte r)

fro nt re a r

Lis t o b je c t (b e fo re )

ne w E ltre a r

ite r

2 55937 2 9374

ite r4

front

List object (after)

front rear

List object (before)

reariter

2 5937 2 593

iter??


Ordered list

Ford: 6:17

The list has an order

Each insert operation should maintain the order

Linear search can be faster to stop for items not found on the list

Sample programs: d_listl.h and prg6_3.cpp


Application considerations re-visit

For the container “order” Will it use an ordered list better?


Summary

Efficiency of operations on linked list and array depends

Reference is a more convenient way to use address than pointer

STL’s list is a doubly linked list and the operations names (method) are the same as what they are in the vector


Reference

Ford: 6.2-3, 9.1-3,5

STL online references http://www.sgi.com/tech/stl http://www.cppreference.com/

Example programs: List.h, TestList.cpp, d_listl.h, and prg6_3.cpp

-- END --

Rossella Lau Lecture 4, DCO20105, Semester A,2005-6 DCO 20105 Data structures and algorithms Lecture 4: C++ and list Usage of Vector and List C++

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