CSE 20232 Lecture 30 – STL Containers

1. CSE 20232Lecture 30 – STL Containers • What is a container class? • STL Containers • vector, list, dequeue • STL Container Adapters • stack, queue, priority_queue • STL Associative Containers • set, map, multiset , multimap • Examples: vector & list

2. What is a container? • A container is a template class that • Holds a collection of data items • Generally is dynamically resizable • Has well defined functions for • Accessing, inserting, removing, and traversing items • The items in some containers are in order, and in others are not • Some allow access by index, some by iterator, and some by key value

3. Vector Container • Vector – like a super array • Resizable using • constructor with size parameter • resize(n) to set size directly • push_back(value) to append a new value • pop_back() to remove last value • Indexed access using [i] operator, • but adding ith element this way does not resize vector • Can contain any class of objects once type is specified in declaration

4. Dequeue container • Dequeue – like a vector except • Values may be added and removed from the beginning as well as the end, using … • push_front(value) and pop_front().

5. Comparing containersarray – vector – dequeue Array size is fixed Vector is expandable at one end Dequeue is expandable at both ends

6. List container • List – is a doubly-linked list • Values are easily (efficiently) inserted and removed at any place in the list • Size is always exactly the size needed for the items stored • Access is sequential only, no indexed access • Traversal of all elements is by using iterators • Manipulation functinos include … • pushback(value), push_front(value), • pop_back() pop_front(), • insert(pos,value) and erase(pos)

7. Iterator • Iterator – like a super pointer • All containers have functions begin() and end() that return iterators • begin() returns an iterator to the first item • end() returns an iterator just past the last iterm • Iterators are moved to the next item (iter++) or the previous item (iter--) • Iterators are dereferenced (*iter) to access the item it points to

8. Lists and iterators iter [ ] iter = pL.begin(); while (iter != pL.end()) { cout << “Node value: “ << *iter << endl; iter++; } This moves the iterator down the list

9. Stack Adapter • Stack – may be a vector, list or dequeue • Has last-in,first-out (LIFO) behavior • Functions • push(value) – adds new value • top() – returns most recently added value • pop() – removes most recently added value pop & top push

10. Queue Adapter • Queue – may be a vector, list or dequeue • Has first-in,first-out (FIFO) behavior • Functions • push(value) – adds new value • front() – returns least recently added value • pop() – removes least recently added value • Priority_queue – like a queue except … • Items have weight or priorities that establish their order in the queue push pop & front

11. Set container • Set – like a mathematical set • Is a balanced search tree behind the scenes • Contains no duplicate values • Data items are stored in order • Iterators traverse items in order • Multiset – like a set except it may contain duplicates 2 12 37

12. Map container • Map – like a database table • Is a balanced search tree behind the scenes • Contains key,value pairs • Data items are stored in order by key • No duplicate keys are allowed • Iterators traverse items in order • Access is by key or iterator • A form of key based indexing is supported • Multimap – like a map except it may contain duplicates Bob:12 Frank:33 Sue:3

13. Where are they defined? • Include the following headers for each type of container needed in your program • <vector> // for vectors • <dequeue> // for dequeues • <list> // for lists • <stack> // for stacks • <queue> // for queues & priority_queues • <set> // for sets and multisets • <map> // for maps and multimaps

14. Using vectors & lists • Example1: vect_list.cpp • Shows use of push_back() with vector and push_front() with list • Shows use of indexes with vector • Shows use of iterator with list • Example2: vect_list2.cpp • Shows use insert() with list • Shows use reverse iterator with list • Shows ordering of both and removal of duplicates in list

15. Vect_list.cpp // vect_list.cpp - JHS 2006 // // This is a demo of the STL vector and list containers. #include <vector> #include <list> #include <iostream> using namespace std; int main() { vector<int> numVect; // declare an integer vector list<int> numList; // declare an integer list int num; // at this point the vector and list are empty and have // essentially no memory space for values

16. Vect_list.cpp // now lets get some values and append them to the vector // and add them to BOTH ends of the list cout << "Enter a series of non-negative integers (-99 to quit)“ << endl; cin >> num; // get a number while (num != -99) // as long as it is not the sentinel { numVect.push_back(num); // append num to end of vector numList.push_front(num); // prepend num to number list numList.push_back(num); // append num to number list cin >> num; // get another number }

17. Vect_list.cpp // finally, lets output the values in both containers // using indices with the vector and iterators with the list cout << "Vector: "; for (int i=0; i<numVect.size(); i++) // output ith valule in vector, could have used an iterator cout << ' ' << numVect[i]; cout << endl; cout << " List: "; list<int>::iterator iter; for (iter = numList.begin(); iter != numList.end(); iter++) // output ith value in list, cannot use an index cout << ' ' << *iter; cout << endl; return 0; }

18. Vect_list2.cpp // vect_list2.cpp - JHS 2006 // // This is a demo of the STL vector and list containers. // showing the use of both as ordered (sorted) sequences #include <vector> #include <list> #include <iostream> #include <string> using namespace std; int main() { vector<string> strVect; // declare a string vector list<string> strList; // declare a string list string word;

19. Vect_list2.cpp cout << "Enter a sequence of words." << endl; while ((cin.peek() != '\n') && (cin >> word)) { // as long as there is another word, get it and ... // insert it into the vector, in order strVect.push_back(word); // append num to end of vector int i = strVect.size() - 1; bool done = false; while ((0 < i) && (! done)) { // compare new value to one on its left if (strVect[i] < strVect[i-1]) // if pair is out of order { string temp = strVect[i]; // swap them strVect[i] = strVect[i-1]; strVect[i-1] = temp; } else done = true; // found first value smaller than new one i--; // move left (down) to next pair }

20. Vect_list2.cpp // now insert word into the list, in order // find last string in list that shoud precede new word list<string>::iterator iter = strList.begin(); while ((iter != strList.end()) && (*iter < word)) iter++; // now insert new word strList.insert(iter,word); // insert word before *itert } // now for some outputs in different orders // output vector values in order cout << " Vector: "; for (int i=0; i<strVect.size(); i++) cout << ' ' << strVect[i]; // output ith value in vector cout << endl;

21. Vect_list2.cpp // output list values in order cout << " List: "; list<string>::iterator iter; for (iter = strList.begin(); iter != strList.end(); iter++) cout << ' ' << *iter; // output ith value in list cout << endl; // remove the duplicates from list for (iter = strList.begin(); iter != strList.end(); iter++) { list<string>::iterator dup = iter; dup++; // point to next item in list while ((dup != strList.end()) && (*dup == *iter)) // erase duplicate and move dup to next item in list dup = strList.erase(dup); }

22. Vect_list2.cpp // show list without duplicates cout << "!dupList: "; for (iter = strList.begin(); iter != strList.end(); iter++) cout << ' ' << *iter; // output ith value in list cout << endl; // show list items in reverse order, using a reverse iterator cout << " revList: "; list<string>::reverse_iterator riter; for (riter = strList.rbegin(); riter != strList.rend(); riter++) cout << ' ' << *riter; // output ith value in reversed list cout << endl; return 0; }