Today’s Objectives

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Today’s ObjectivesToday’s Objectives

Announcements• The Final Exam will be on Monday, 31-Jul, at 6 p.m. –

There is no alternate time and no makeup!

Intro to the Standard Template Library (STL) (Ch. 21)• Containers

– vector class– list class– map class

• Iterators• Algorithms

Final Exam Review

26-Jul-200626-Jul-2006

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Intro to the STLIntro to the STL

Chapter 23

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Standard Template Library (STL)Standard Template Library (STL)

Part of the C++ standard library

Defines reusable components that we can add to our programs

Three types of components in the STL• Containers• Iterators• Algorithms

Intro to the STL (Deitel, 1112)Intro to the STL (Deitel, 1112)

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ContainersContainers

Container = a data structure that stores a collection of objects

The stored objects are called “elements” Examples of containers

• Array• vector• Classes like RentalItemList• Linked list

Bottom line – Containers are used a lot in our programs, so we could save time if we had a library of readymade container classes that are guaranteed to work correctly and efficiently.

Intro to the STL (Deitel, 1112; Goodrich, 242)Intro to the STL (Deitel, 1112; Goodrich, 242)

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STL ContainersSTL Containers

Template classes that can be used to hold collections of data vector class

• #include <vector>• Used like an array, but dynamically re-sizable

list class• #include <list>• Used like a linked list

set class and multiset class• #include <set>• Sorts elements automatically

map class and multimap class• #include <map>• Associative arrays


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STL vector ClassSTL vector Class

Contains elements in a linear sequence Its elements are accessible with operator[]

#include <vector>

vector<char> collection;vector<Customer> customers;

Works like an array, but it is automatically re-sized when it needs more space


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Using a vector ObjectUsing a vector Object

#include <vector>using namespace std;int main(){

Intro to the STL (Deitel, 1125–7)Intro to the STL (Deitel, 1125–7)

Include the header file

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vector<char> collection;


Instantiate a vector object that will hold char data

Name of the class The object name

Template parameter – type of data the vector will hold

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vector<char> collection;collection.push_back('c');collection.push_back('a');collection.push_back('b');


Add some data

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vector<char> collection;collection.push_back('c');collection.push_back('a');collection.push_back('b');cout << collection.size() << endl;


Number of elements in the vector = 3

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vector<char> collection;collection.push_back('c');collection.push_back('a');collection.push_back('b');cout << collection.size() << endl;collection.pop_back();


Removing an element

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Using a vector like an arrayUsing a vector like an array


vector<char> collection;collection.resize(3);


Before using an array index to insert values into a vector, make sure that the vector has enough room for your data

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Using a vector like an arrayUsing a vector like an array


vector<char> collection;collection.resize(3);collection[0] = 'c';collection[1] = 'a';collection[2] = 'b';


Add some data by using the assignment operator

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vector<char> collection;collection.resize(3);collection[0] = 'c';collection[1] = 'a';collection[2] = 'b';for( int i=0; i<collection.size(); ++i )

cout << collection[i] << endl;


We can refer to each element in the vector by using an index, just like with an array

• The range is not checked, so an out-of-range error can occur

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vector<char> collection;collection.resize(3);collection[0] = 'c';collection[1] = 'a';collection[2] = 'b';for( int i=0; i<collection.size(); ++i )

cout << collection[i] << endl;try{

cout << collection.at(256) << endl;}catch( out_of_range e ){cout << e.what() << endl;}


When the at() member function is used with an index, the range is checked, and an out-of-range exception can be thrown.

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STL list ClassSTL list Class

Contains elements in a linear sequence

#include <list>

list<char> collection;list<Customer> customers;

Works like a linked list


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Using a list ObjectUsing a list Object

#include <list>using namespace std;int main(){

list<char> collection;

Intro to the STL (Deitel, 1133–1137, Josuttis,)Intro to the STL (Deitel, 1133–1137, Josuttis,)

Instantiate a list object that will hold char data

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list<char> collection;collection.push_back('c');collection.push_front('a');collection.push_front('b');collection.push_back('b');


Add some data

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list<char> collection;collection.push_back('c');collection.push_front('a');collection.push_front('b');collection.push_back('b');collection.remove('b');


Removing all elements equal to ‘b’

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list<char> collection;collection.push_back('c');collection.push_front('a');collection.push_front('b');collection.push_back('b');collection.remove('b');cout << collection.size() << endl;


Will print ‘2’

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list<char> collection;collection.push_back('c');collection.push_front('a');collection.push_front('b');collection.push_back('b');collection.remove('b');cout << collection.size() << endl;while( !collection.empty() ){

cout << collection.front() << endl;collection.pop_front();

}}


Since access by operator[] is not allowed, this loop iterates through the list by removing each element, a better way is to use an iterator.

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STL map ClassSTL map Class

STL ordered dictionary class

#include <map>

map<keyType,elementType>

map<string,string> passwords;

Does not allow duplicates• If duplicates are needed, use the multimap

class

Intro to the STL (Deitel, 1145; Josuttis, 90, 194)Intro to the STL (Deitel, 1145; Josuttis, 90, 194)

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Using a Map as anAssociative ArrayUsing a Map as anAssociative Array

Associative array = an array where the index can be any datatype

Insertion is done with operator[] Examples

map<string,string> password;password["Bob"] = "zebra";

map<string,double> stockValue;stockValue["MSFT"] = 25.53;stockValue["IBM"] = 91.94;cout << "Microsoft price: " << stockValue["MSFT"];

Intro to the STL (Deitel, 1145; Josuttis, 90, 194)Intro to the STL (Deitel, 1145; Josuttis, 90, 194)

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Example of Using a MapExample of Using a Map

int main(){

string word; map<string,int> wordFrequency; //Count frequency of each word

ifstream bookFile( "MobyDick.txt" ); while( !bookFile.eof() ) {

bookFile >> word;wordFrequency[word]++;

} bookFile.close(); cout << "\nUnique words = " << wordFrequency.size() << endl;

map<string,int>::iterator pos; for( pos=wordFrequency.begin(); pos!=wordFrequency.end(); ++pos ){

cout << pos->first << " " << pos->second << endl; }}

Intro to the STL (Christiansen,150; Lippman,1081)Intro to the STL (Christiansen,150; Lippman,1081)

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STL IteratorsSTL Iterators

An iterator is a class used to create objects that give us access to the elements inside a container

They are called “iterators” because they are often used to sequentially iterate or “loop” through all the elements in a container

Iterators are implemented as part of the container class with which we use them – all container classes have them

Some types of iterators that may be used with most container classes• iterator• const_iterator• reverse_iterator

Intro to the STL (Deitel, 1117; Josuttis, 83–86)Intro to the STL (Deitel, 1117; Josuttis, 83–86)

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Using an STL IteratorUsing an STL Iterator

vector<char> coll;coll.push_back('c');coll.push_back('a');coll.push_back('b');

Intro to the STL (Josuttis, 83–86)Intro to the STL (Josuttis, 83–86)

Create a vector of chars and put some chars in it

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vector<char>::iterator pos;


Instantiate an iterator that can be used with a vector of chars

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for( pos = coll.begin(); pos != coll.end(); ++pos)


Create a for loop

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InitializationAssign a starting value to the iterator

Every collection class has a begin() member function that returns an iterator representing its first element.

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ConditionLoop is executed only if this is true

Every collection class has a end() member function that returns an iterator representing the position after the last element.

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In the expression evaluated at the end of each loop, the iterator behaves like a pointer.

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for( pos = coll.begin(); pos != coll.end(); ++pos){

cout << *pos << " ";}


In the loop, we can use the iterator like a pointer again, so that we can get the value stored at this position.

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STL AlgorithmsSTL Algorithms

In the STL, algorithms are global functions STL algorithms are used with iterators #include <algorithm> Some STL algorithms

• copy• count• find• min_element• max_element• reverse• sort• unique

Intro to the STL (Deitel, 1152; Josuttis, 94)Intro to the STL (Deitel, 1152; Josuttis, 94)

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Using STL AlgorithmsUsing STL Algorithms




Create a vector of chars and put some chars in it

Instantiate an iterator that can be used with a vector of chars

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pos = min_element( coll.begin(), coll.end() );


Call an STL algorithm to locate the minimum element in a collection.

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pos = min_element( coll.begin(), coll.end() );


Returns an iterator for the position of the minimum element.

Arguments specify the range of elements to examine in the collection.

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pos = min_element( coll.begin(), coll.end() );cout << "Min = " << *pos << endl;


Use the iterator like a pointer again, to get the value stored at this position.

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pos = min_element( coll.begin(), coll.end() );cout << "Min = " << *pos << endl;

pos = max_element( coll.begin(), coll.end() );cout << "Max = " << *pos << endl;


Another STL algorithm locates the maximum element in a collection.

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sort( coll.begin(), coll.end() );

Intro to the STL (Josuttis, 95–96, 123)Intro to the STL (Josuttis, 95–96, 123)

Sorting the elements in a collection.

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Using Arrays with STL AlgorithmsUsing Arrays with STL Algorithms

char coll[] = {'c','a','a','b'};

sort( coll, coll+4 );


The first argument must be a pointer to the beginning element in the range of elements to be sorted

The second argument must be a pointer to the position after the last element

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vector<Customer> coll;

coll.push_back(Customer("Alan","Turing"));

coll.push_back(Customer("Charles","Babbage"));

coll.push_back(Customer("Ada","Lovelace"));

bool criteria(const Customer& c1, const Customer& c2){return c1.getLastName() < c2.getLastName();

}


When the elements in an STL collection are objects, a “binary predicate” can be defined for the sort() algorithm to use.

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}


A “predicate” is a function that returns a boolean value, and they are often used with STL algorithms.

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}


A “binary predicate” usually compares an attribute of two arguments.

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}

sort( coll.begin(), coll.end(), criteria );


The name of the binary predicate is passed as the third argument

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sort( coll.begin(), coll.end() );


Another approach that works equally well is to define operator< in the class, then the criteria is not required.

class Customer{public:

bool operator<( const Customer& rhs ){return this->lname < rhs.lname;

}//...};

class Customer{public:

bool operator<( const Customer& rhs ){return this->lname < rhs.lname;

}//...};

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pos = find( coll.begin(), coll.end(), 'b' );

if( pos == coll.end() ) cout << "\nNot found\n";else cout << "\nFound: " << *pos << "\n";


find() can be used to find an element in a collection.

target

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vector<Customer> coll;coll.push_back(Customer("Alan","Turing"));coll.push_back(Customer("Charles","Babbage"));coll.push_back(Customer("Ada","Lovelace"));

vector<char>::iterator pos;Customer alan("Alan","Turing");pos = find( coll.begin(), coll.end(), alan );

if( pos == coll.end() ) cout << "\nNot found\n";else cout << "\nFound: " << (*pos).toString() << "\n";


The target can be an object, but only if operator== is defined

class Customer{public: bool operator==( const Customer& rhs ){ return ( (this->lname == rhs.lname) && (this->fname == rhs.fname) ); }//...};

class Customer{public: bool operator==( const Customer& rhs ){ return ( (this->lname == rhs.lname) && (this->fname == rhs.fname) ); }//...};

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pos = find( coll.begin(), coll.end(), 'b' );

if( pos != coll.end() )coll.erase( pos );


An iterator can sometimes be used as an argument to a member function of a collection

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vector<char> coll;coll.push_back('c');coll.push_back('a');coll.push_back('a');coll.push_back('b');

coll.erase( remove(coll.begin(),coll.end(),'a'), coll.end() );


To remove all elements that have a particular value, the remove function can be used.

However, it only works properly for a vector if it’s used with the vector’s erase member function.

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reverse( coll.begin(), coll.end() );


Reversing the elements in a collection.

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Final Exam ReviewFinal Exam Review

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Final ExamFinal Exam

30% of your grade for the course Jul. 31 at 6 p.m. in the regular classroom No makeup exam No alternate time Closed book Closed notes


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Material CoveredMaterial Covered

Anything in the slides and handouts

Deitel text, chapters 1–18, 21.1–21.4, and 23

Most of the questions will focus on the material covered since the Midterm Exam, but it is still important to know the material from the first part since it provides the foundation


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Test FormatTest Format

Approximately 20 questions Short C++ programs

• Write the C++ code for a derived class from a given UML class diagram – the code should be complete and compilable

• Write a short C++ code fragment that is complete and compilable

Short answers – write a line of C++ code Simple UML diagrams – e.g. draw a diagram showing

composition (has-a) or inheritance (is-a) associations Multiple choice Locate errors in code


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Suggestions for StudyingSuggestions for Studying

Look at the Learning Objectives on the course syllabus Concentrate your study time on the major topics that we have

covered in class Use the Final Exam Review handout as a study guide – download it

from the Files area of our Discussion Group Make sure that you know what the object-oriented C++ features do

and how to use them• Can you write a C++ derived class, including the data members and

fully implemented member functions?• Do you know how virtual member functions work?• Can you instantiate an object from a template class?• Do you know how to use a try-catch block with exceptions?• Do you know how to open a file for input?• Do you know how to add a new Node to a linked list?


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ReferencesReferences

C++ Language Reference (MS Visual C++ Online Help), Redmond, Washington: Microsoft Corporation, 2001.

Deitel, H. M., and P. J. Deitel, C++ How to Program, Fifth Edition. Upper Saddle River, NJ: Prentice Hall, 2005.

Goodrich, M. T., R. Tamassia, and D. Mount, Data Structures and Algorithms in C++. Hoboken, NJ: John Wiley & Sons, Inc., 2004.

Josuttis, Nicolai M., The C++ Standard Library, A Tutorial and Reference. Boston: Addison-Wesley, 1999.

Lippman, Stanley B., and Josee Lajoie, C++ Primer. Boston: Addison-Wesley, 1998.

Documents

Today’s Objectives