STL Overview Prof Brinton Gordon College 1 Standard

STL Overview Prof. Brinton Gordon College 1

Standard Template Library (STL) • • Part of ISO-OSI Standard C++ Library 1998 Object oriented programming is about reuse – STL has many reusable components – Divided into 1. Containers - manage collections of objects 2. Iterators - step through the elements of collections 3. Algorithms - used to process the elements of collections 2

Introduction to Containers • Three types of containers 1. sequence containers - ordered collections vector, deque, list 2. associative containers - sorted collections set, multiset, map, multimap 3. container adapters • • Stacks, queues, priority queues Near-containers - similar to containers, without all the capabilities – C-like arrays – string – bitset - for maintaining sets of 1/0 flag values 1. valarray - high-speed mathematical vector operations The containers have similar functions 3

Introduction to Containers • list direct access to any element rapid insertion at front or back direct access to any element rapid insertion and deletion anywhere • set • multiset • map, multimap rapid lookup, no duplicates rapid lookup, duplicates store key/value pairs • stack • queue • priority_queue last-in-first-out first-in-first-out highest priority element is first • vector • deque 4

Introduction to Containers • Common member functions of all STL containers: constructors, destructors assignment, all comparison operators swap empty max_size • Use if(c. empty()) not if(c. size() == 0) 5

Introduction to Iterators • Iterators are similar to pointers – point to element in a container – iterator operators uniform for all containers • * dereferences, ++ advances pointer • container. begin() returns iterator pointing to first element • container. end() returns iterator pointing after last element it for(it = c. begin(); it != c. end(); it++) { *it… } 6

Iterator Categories • Bidirectional iterators – Iterate in 2 directions: p++ or p-– list, set, multiset, map, multimap – Use != instead of < or > in loops • Random access iterators – Have all properties of bidirectional iterators – Can also perform random access • +, -, <, > – vector, deque, strings 7

Constness of Iterators • Examples vector<int>: : iterator it = v. begin(); vector<int>: : const_iterator cit = v. begin(); *cit = 24; // does not compile *it = 24; // ok void fct(const vector<int>& v) { vector<int>: : iterator it; it = v. begin(); // does not compile } 8

Constness of Iterators • Examples (Fixed) vector<int>: : iterator it = v. begin(); vector<int>: : iterator cit = v. begin(); *cit = 24; // ok *it = 24; // ok void fct(const vector<int>& v) { vector<int>: : const_iterator it; it = v. begin(); // ok } 9

Iterator Adapters • Everything that behaves like an iterator is an iterator – Insert iterator (inserters) – Stream iterator - allow you to use a stream as a source or dest of an algorithm. – Reverse iterators • Example: list<Point>: : reverse_iterator r 1 = L. rbegin(), r 2 = L. rend(); 10

Iterator Adapters vector<int> coll; back_insert_iterator<vector<int> > iter(coll); *iter = 1; iter++; *iter = 2; iter++; *iter = 3; PRINT_ELEMENTS(coll); back_inserter(coll) = 44; back_inserter(coll) = 55; PRINT_ELEMENTS(coll); coll. reserve(2*coll. size()); copy (coll. begin(), coll. end(), // source back_inserter(coll)); // destination PRINT_ELEMENTS(coll); Results: 123 1 2 3 44 55 11

Introduction to Algorithms • STL algorithms used generically across containers: – operate on elements indirectly through iterators – often operate on sequences of elements defined by pairs of iterators – algorithms often return iterators, such as find() – premade algorithms save programmers time and effort 12

Sequence Containers • Three sequence containers – vector - based on arrays – deque - based on arrays – list - robust linked list 13

vector Sequence Container • vector – – – #include <vector> data structure with contiguous memory locations use the subscript operator [] used when data must be sorted and easily accessible when memory exhausted • allocates a larger, contiguous area of memory • copies itself there • deallocates the old memory – has a random access iterator 14

vector Sequence Container • Declarations – vector <type> v; – vector <type> v(7812); – template <class It> vector<type> v(It begin, It end); – type - int, float, Point, whatsoever • Iterators: – vector<type>: : const_iterator it; vector<type>: : iterator it = v. begin(); *(it 1 + 5) = 34; 15

vector Sequence Container (II) • vector functions, for vector object v v. push_back(value) - add element to end v. size() - current size of vector v. capacity() - how much vector can hold before reallocation v. reserve(n) - allow vector to avoid reallocation v. insert( pointer, value ) - inserts value before pointer. 16

vector Sequence Container (III) • vector functions and operations v. erase( pointer ) • remove element from container v. erase( pointer 1, pointer 2 ) • remove elements starting from pointer 1 and up to (not including) pointer 2. v. clear() • erases entire container. v[element. Number] = value; • assign value to an element v. at[element. Number] = value; • as above, with range checking • throws out_of_bounds exception 17

list Sequence Container • list container – – #include <list> efficient insertion/deletion anywhere in container doubly-linked list bidirectional iterators • There exists also a non-standard slist – singly-linked list – forward iterator 18

list Sequence Container (II) • list functions for list. Object and other. Object list. Object. sort() • sorts in ascending order list. Object. splice(iterator, other. Object); • inserts values from other. Object before location of iterator list. Object. merge(other. Object) • removes other. Object and inserts it into list. Object, sorted list. Object. unique() • removes duplicate elements list. Object. swap(other. Object); • exchange contents list. Object. assign(iterator 1, iterator 2) • replaces contents with elements in range of iterators list. Object. remove(value) • erases all instances of value 19

deque Sequence Container • deque ("deek") - double-ended queue – – #include <deque> indexed access using [] efficient insertion/deletion in front and back non-contiguous memory: "smarter" pointers • same basic operations as vector – adds push_front / pop_front - insertion/deletion at beginning of deque 20

Associative Containers • Associative containers – provide direct access to store and retrieve elements via keys (search keys) • 4 types: multiset, multimap and map – keys in sorted order – multiset and multimap allow duplicate keys – multimap and map allow keys and associate values 21

Excursion: Function Objects template <class T> struct less { bool operator()(const T& lhs, const T& rhs) const { return lhs < rhs; } }; less<int> is_smaller; if(is_smaller(45, 34)){. . } 22

multiset Associative Container • multiset - fast storage, retrieval of keys – allows duplicates • Ordering by comparator function object less<type> - sorts keys in ascending order multiset< int, less<int> > integers; • CGAL comparator function objects typedef CGAL: : Cartesian<double> K; multiset< K: : Point_2, K: : Compare_xy_2 > points; 23

multiset Associative Container (II) • Functions for multiset object ms. Object – ms. Object. insert(value) - inserts value – ms. Object. find(value) - returns iterator to first instance of value, or ms. Object. end() – ms. Object. lower_bound(value)- returns iterator to first location of value – ms. Object. upper_bound(value)- returns iterator to location after last occurrence of value – for a pair object p p = ms. Object. equal_range(value) • sets first and second to lower_bound and upper_bound for a given value 24

set Associative Container • set – – implementation identical to multiset unique keys - duplicates ignored and not inserted supports bidirectional iterators (but not random access) #include <set> 25

map Associative Container • map – – fast storage/retrieval of unique key/value pairs #include <map> one-to-one mapping (duplicates ignored) use [] to access values for map<int, double> M; M[30] = 4000. 21; sets the value of key 30 to 4000. 21 – if subscript not in map, creates new key/value pair – Efficiency remark: Use insert to insert, operator[] to update 26

Non Standard Associative Container • hash_(multi)set, hash_(multi)map – – Not part of the standard, but provided by some STLs REALLY fast storage/retrieval of unique key/value pairs Based on hashing and not on binary trees No order, but provide iterators 27

Container Adapters • container adapters: stack, queue, priority_queue – – – not first class containers do not support iterators do not provide actual data structure programmer can select implementation of the container adapters have member functions push() and pop() 28

stack Adapter • stack – – insertions and deletions at one end last-in-first-out data structure implemented with vector, list, and deque (default) #include <stack> • Declarations stack<type, vector<type> > my. Stack; stack<type, list<type> > my. Other. Stack; stack<type> another. Stack; 29

queue Adapter • queue - insertions at back, deletions at front – first-in-first-out data structure – implemented with list or deque – #include <queue> • Functions – – push(element) - (push_back) add to end pop(element) - (pop_front) remove from front empty() - test for emptiness size() - returns number of elements • Example: queue <double> values; values. push(1. 2); values. push(3. 4); values. pop(); //create queue // values: 1. 2 3. 4 // values: 1. 2 30

priority_queue Adapter • insertions in sorted order, deletions from front – implemented with vector or deque – highest priority element always removed first • heapsort puts largest elements at front • less<T> by default, programmer can specify another • Functions – – push - (push_back then reorder elements) pop - (pop_back to remove highest priority element) size empty 31

Algorithms • Before STL – class libraries were incompatible among vendors – algorithms built into container classes • STL separates containers and algorithms – easier to add new algorithms – not member functions of containers, global functions that operate with iterators (reduces the amount of code) • Not necessarily intuitive…not all combinations possible. – General fundamental services on containers: • Searching • Sorting • Copying • Reordering • Modifying • Numeric processing 32

#include <iostream> #include <vector> #include <algorithm> using namespace std; Algorithms Example int main() { vector<int> coll; vector<int>: : iterator pos; coll. push_back(2); coll. push_back(5); coll. push_back(4); coll. push_back(1); coll. push_back(6); coll. push_back(3); 254163 pos = min_element (coll. begin(), coll. end()); cout << "min: " << *pos << endl; pos = max_element (coll. begin(), coll. end()); cout << "max: " << *pos << endl; } 1 6 sort (coll. begin(), coll. end()); 123456 pos = find (coll. begin(), coll. end(), 3); reverse (pos, coll. end()); 126543 33

Algorithms • Ranges pos = min_element (coll. begin(), coll. end()); • Multiple Ranges if (equal (coll 1. begin(), coll 1. end(), coll 2. begin()) { … } Algorithm Categories: 1. 2. 3. 4. 5. 6. 7. Nonmodifying - count, for_each, min_element… Modifying - copy, transform, merge, replace, fill… Removing - remove, unique… Mutating - reverse, rotate, random_shuffle… Sorting - sort_heap, make_heap, sort, … Algorithms for Sorted Ranges - binary_search, merge, … Numeric - accumulate, inner_product, … 34

Non-Modifying Algorithm: for_each void print (int elem) { cout << elem << ' '; } int main() { vector<int> coll; INSERT_ELEMENTS(coll, 1, 9); // call print() for each element for_each (coll. begin(), coll. end(), print); cout << endl; } 35

Modifying Algorithm: copy { vector<int> coll 1; list<int> coll 2; INSERT_ELEMENTS(coll 1, 1, 9); copy (coll 1. begin(), coll 1. end(), back_inserter(coll 2)); copy (coll 2. begin(), coll 2. end(), ostream_iterator<int>(cout, " ")); cout << endl; copy (coll 1. rbegin(), coll 1. rend(), coll 2. begin()); } 36

Modifying Algorithm: unique int source[] = { 1, 4, 4, 6, 1, 2, 2, 3, 1, 6, 6, 6, 5, 7, 5, 4, 4 }; int source. Num = sizeof(source)/sizeof(source[0]); list<int> coll; copy (source, source+source. Num, back_inserter(coll)); list<int>: : iterator pos; pos = unique (coll. begin(), coll. end()); copy (coll. begin(), pos, ostream_iterator<int>(cout, " " // source)); cout << "nn"; copy (source, source+source. Num, coll. begin()); coll. erase (unique (coll. begin(), coll. end(), greater<int>()), coll. end()); 37

accumulate, transform • list<int> L(. . ); int sum = accumulate(L. begin(), L. end(), 0, plus<int>()); • transform(istream_iterator<Point>(cin), istream_iterator<Point>(), ostream_iterator<double>(cout), mem_fun_ref(Point: : x)); 39

Basic Searching Algorithms • find(iterator 1, iterator 2, value) – returns iterator pointing to first instance of value • find_if(iterator 1, iterator 2, function) – like find, but returns an iterator when function returns true. • binary_search(iterator 1, iterator 2, value) – searches an ascending sorted list for value using a binary search 40

Sorting Algorithms • sort(begin, end) • partial_sort(begin, begin+N, end) – finds first N and sorts them • nth_element(begin, begin+N, end) – finds first N, not sorted • partition(begin, end, function) – splits in two intervals • stable_sort, stable_partition • Remarks – All take optionaly a comparison function – std: : sort is faster than clib sort 41

equal, mismatch, lexicographical_compare • Functions to compare sequences of values • equal – returns true if sequences are equal (uses ==) – returns false if of unequal length equal(iterator 1, iterator 2, iterator 3); – compares sequence from iterator 1 up to iterator 2 with the sequence beginning at iterator 3 – Containers can be of different types 42

fill, fill_n, generate_n • STL functions, change containers. • fill - changes a range of elements (from iterator 1 to iterator 2) to value – fill(iterator 1, iterator 2, value); • fill_n - changes specified number of elements, starting at iterator 1 – fill_n(iterator 1, quantity, value); • generate - like fill, but calls a function for value – generate(iterator 1, iterator 2, function); • generate_n - like fill_n, but calls function for value – generate(iterator 1, quantity, value) 43

swap, iter_swap and swap_ranges • swap(element 1, element 2) - exchanges two values swap( a[ 0 ], a[ 1 ] ); • iter_swap(iterator 1, iterator 2) - exchanges the values to which the iterators refer • swap_ranges(iterator 1, iterator 2, iterator 3) - swap the elements from iterator 1 to iterator 2 with the elements beginning at iterator 3 44

copy_backward, merge, unique, reverse • copy_backward(iterator 1, iterator 2, iterator 3) – copy the range of elements from iterator 1 to iterator 2 into iterator 3, but in reverse order. • merge(iter 1, iter 2, iter 3, iter 4, iter 5) – ranges iter 1 -iter 2 and iter 3 -iter 4 must be sorted in ascending order. – merge copies both lists into iter 5, in ascending order. • unique(iter 1, iter 2) - removes duplicate elements from a sorted list, returns iterator to new end of sequence. • reverse(iter 1, iter 2)- reverses elements in the range of iter 2. iter 1 to 45

Remove does (not) Remove • Member function: L. remove(Point(0, 0)); • Algorithm moves at end: list<Point> L(istream_iterator<Point>(cin), istream_iterator<Point>()); list<Point>: : iterator eit; eit = remove(L. begin(), L. end(), Point(0, 0)); L. erase(eit, L. end()); 46

Other Features of the STL • • • Streams strings, wide strings locales (for internationalization) numerical valarray 47

References • N. M. Josuttis, The C++ Standard Library, Addison-Wesley 2001 48