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Today’s Objectives

26-Jul-2006. Today’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.

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Today’s Objectives

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  1. 26-Jul-2006 Today’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

  2. Intro to the STL Chapter 23

  3. Intro to the STL (Deitel, 1112) 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

  4. Intro to the STL (Deitel, 1112; Goodrich, 242) Containers • 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.

  5. Intro to the STL (Deitel, 1112) STL Containers • Template classes that can be used to hold collections of data • vectorclass • #include <vector> • Used like an array, but dynamically re-sizable • listclass • #include <list> • Used like a linked list • setclass andmultisetclass • #include <set> • Sorts elements automatically • mapclassand multimapclass • #include <map> • Associative arrays

  6. Intro to the STL (Deitel, 1125) STL 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

  7. Intro to the STL (Deitel, 1125–7) Using a vector Object #include <vector> using namespace std; int main(){ Include the header file

  8. The object name Name of the class Template parameter – type of data the vector will hold Intro to the STL (Deitel, 1125–7) Using a vector Object #include <vector> using namespace std; int main(){ vector<char> collection; Instantiate a vector object that will hold char data

  9. Intro to the STL (Deitel, 1125–7) Using a vector Object #include <vector> using namespace std; int main(){ vector<char> collection; collection.push_back('c'); collection.push_back('a'); collection.push_back('b'); Add some data

  10. Intro to the STL (Deitel, 1125–7) Using a vector Object #include <vector> using namespace std; int main(){ 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

  11. Intro to the STL (Deitel, 1125–7) Using a vector Object #include <vector> using namespace std; int main(){ 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

  12. Intro to the STL (Deitel, 1125–7) Using a vector like an array #include <vector> using namespace std; int main(){ 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

  13. Intro to the STL (Deitel, 1125–7) Using a vector like an array #include <vector> using namespace std; int main(){ vector<char> collection; collection.resize(3); collection[0] = 'c'; collection[1] = 'a'; collection[2] = 'b'; Add some data by using the assignment operator

  14. Intro to the STL (Deitel, 1125–7) Using a vector Object #include <vector> using namespace std; int main(){ 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

  15. Intro to the STL (Deitel, 1125–7) Using a vector Object #include <vector> using namespace std; int main(){ 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.

  16. Intro to the STL (Deitel, 1133) STL list Class • Contains elements in a linear sequence • #include <list> • list<char> collection;list<Customer> customers; • Works like a linked list

  17. Intro to the STL (Deitel, 1133–1137, Josuttis,) Using a list Object #include <list> using namespace std; int main(){ list<char> collection; Instantiate a list object that will hold char data

  18. Intro to the STL (Deitel, 1133–1137, Josuttis,) Using a list Object #include <list> using namespace std; int main(){ list<char> collection; collection.push_back('c'); collection.push_front('a'); collection.push_front('b'); collection.push_back('b'); Add some data

  19. Intro to the STL (Deitel, 1133–1137, Josuttis,) Using a list Object #include <list> using namespace std; int main(){ 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’

  20. Intro to the STL (Deitel, 1133–1137, Josuttis,) Using a list Object #include <list> using namespace std; int main(){ 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’

  21. Intro to the STL (Deitel, 1133–1137, Josuttis,) Using a list Object #include <list> using namespace std; int main(){ 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.

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

  23. Intro to the STL (Deitel, 1145; Josuttis, 90, 194) Using 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"];

  24. Intro to the STL (Christiansen,150; Lippman,1081) Example 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; } }

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

  26. Intro to the STL (Josuttis, 83–86) Using an STL Iterator vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); Create a vector of chars and put some chars in it

  27. Intro to the STL (Josuttis, 83–86) Using an STL Iterator vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; Instantiate an iterator that can be used with a vector of chars

  28. Intro to the STL (Josuttis, 83–86) Using an STL Iterator vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; for( pos = coll.begin(); pos != coll.end(); ++pos) Create a for loop

  29. Intro to the STL (Josuttis, 83–86) Using an STL Iterator vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; for( pos = coll.begin(); pos != coll.end(); ++pos) Initialization Assign a starting value to the iterator Every collection class has a begin() member function that returns an iterator representing its first element.

  30. Intro to the STL (Josuttis, 83–86) Using an STL Iterator vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; for( pos = coll.begin(); pos != coll.end(); ++pos) Condition Loop 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.

  31. Intro to the STL (Josuttis, 83–86) Using an STL Iterator vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; for( pos = coll.begin(); pos != coll.end(); ++pos) In the expression evaluated at the end of each loop, the iterator behaves like a pointer.

  32. Intro to the STL (Josuttis, 83–86) Using an STL Iterator vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; 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.

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

  34. Intro to the STL (Josuttis, 95–96) Using STL Algorithms vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; Create a vector of chars and put some chars in it Instantiate an iterator that can be used with a vector of chars

  35. Intro to the STL (Josuttis, 95–96) Using STL Algorithms vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; pos = min_element( coll.begin(), coll.end() ); Call an STL algorithm to locate the minimum element in a collection.

  36. Returns an iterator for the position of the minimum element. Arguments specify the range of elements to examine in the collection. Intro to the STL (Josuttis, 95–96) Using STL Algorithms vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; pos = min_element(coll.begin(),coll.end());

  37. Intro to the STL (Josuttis, 95–96) Using STL Algorithms vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; 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.

  38. Intro to the STL (Josuttis, 95–96) Using STL Algorithms vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; 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.

  39. Intro to the STL (Josuttis, 95–96, 123) Using STL Algorithms vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); sort( coll.begin(), coll.end() ); Sorting the elements in a collection.

  40. Intro to the STL (Josuttis, 95–96) Using 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

  41. Intro to the STL (Josuttis, 95–96, 123) Using STL Algorithms 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.

  42. Intro to the STL (Josuttis, 95–96, 123) Using STL Algorithms 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(); } A “predicate” is a function that returns a boolean value, and they are often used with STL algorithms.

  43. Intro to the STL (Josuttis, 95–96, 123) Using STL Algorithms 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(); } A “binary predicate” usually compares an attribute of two arguments.

  44. Intro to the STL (Josuttis, 95–96, 123) Using STL Algorithms 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(); } sort( coll.begin(), coll.end(), criteria ); The name of the binary predicate is passed as the third argument

  45. Intro to the STL (Josuttis, 95–96, 123) Using STL Algorithms vector<Customer> coll; coll.push_back(Customer("Alan","Turing")); coll.push_back(Customer("Charles","Babbage")); coll.push_back(Customer("Ada","Lovelace")); sort( coll.begin(), coll.end() ); class Customer{ public: bool operator<( const Customer& rhs ){ return this->lname < rhs.lname; } //... }; Another approach that works equally well is to define operator< in the class, then the criteria is not required.

  46. Intro to the STL (Josuttis, 95–96, 341) Using STL Algorithms vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; 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

  47. Intro to the STL (Josuttis, 95–96, 341) Using STL Algorithms 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) ); } //... };

  48. Intro to the STL (Josuttis, 95–96) Using STL Algorithms vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; 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

  49. Intro to the STL (Josuttis, 95–96) Using STL Algorithms 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.

  50. Intro to the STL (Josuttis, 95–96) Using STL Algorithms vector<char> coll; coll.push_back('c'); coll.push_back('a'); coll.push_back('b'); vector<char>::iterator pos; reverse( coll.begin(), coll.end() ); Reversing the elements in a collection.

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