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STL Library - Overview

STL Library - Overview. Standard template library accepted in July 1994 into C++ ANSI Standard STL library provides containers, iterators and algorithms designed to work efficiently work parametrically work orthogonally. vector. queue. map. previous. next. begin. end.

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STL Library - Overview

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  1. STL Library - Overview • Standard template library accepted in July 1994 into C++ ANSI Standard • STL library provides containers, iterators and algorithms designed to • work efficiently • work parametrically • work orthogonally 5/8/2002 1

  2. vector queue map previous next begin end STL - Standard Template Library • Efficient library for basic data structures • Navigation of containers using iterator classes • Algorithms for their use search functions sort functions 5/8/2002 2

  3. STL Based on Templates • Parametric - instantiated with different types • Components used with each other • Uses templates • Native types • User provided types 5/8/2002 3

  4. vectors maps queues STL - Standard Template Library • Parametric - types instantiated • Library for data structures • Provides tools for navigation over containers using iterator classes • begin, end, previous, next • Provides algorithms for their use • sorting, searching functions 5/8/2002 4

  5. Array Example (1 of 3) • #include <iostream.h> • #include <stdlib.h> • #include <time.h> • #include <algorithm> • //QUICKSORT using an vector class • inline double secs(clock_t c) • { return (double)c/CLOCKS_PER_SEC;} • #define N 1000000 • int v[N]; 5/8/2002 5

  6. Array Example (2 of 3) • main() • { • time_t c; • cout <<"\ntime start = " << secs(clock()); • for (int i =0 ; i < N; ++i) • v[i] = rand(); 5/8/2002 6

  7. Array Example (3 of 3) • //uses a quicksort algorithm • cout <<"\nstl sort start = " << secs(c = clock()); • std::sort(v, v + N); • cout <<"\n stl sort = " << secs( clock()-c); • cout << endl; • } • On my pentium 166 megahertz approx 2.8 secs for 1 million keys • On moondance 10 million keys approx 11 seconds 5/8/2002 7

  8. Comments on Array • namespace std::sort() • Used with ordinary vectors • Speedy - compares to hand coded quick sort • Pointer values v and v + N • v is begin address • v + N is end address (one past) 5/8/2002 8

  9. vector list deque set multiset map multimap Two Varieties of Containers • Sequence - ordered by sequence of elements • Associative - keys for looking up elements • Both varieties share a similar interface 5/8/2002 9

  10. Typical Container Interfaces • Constructors • default constructors, copy constructors • Element access • Element insertion • Element deletion • Destructor • Iterators 5/8/2002 10

  11. Overview of Containers • Common set of properties • Constructors and destructors • Element access, insertion and deletion • Allocate and manage memory • Associated allocator objects 5/8/2002 11

  12. Container Members for CAN CAN() default constructor CAN(c) copy constructor c.begin() beginning location of CAN c c.end() ending location of CAN c c.rbegin() beginning for reverse iterator c.rend()ending for reverse iterator c.size() number of elements in CAN c.max_size() largest possible size c.empty() true if the CAN is empty c.swap(d) swap two CANs 5/8/2002 12

  13. Container Operators • == != < > <= >= 5/8/2002 13

  14. Typical Container Algorithm (1 of 2) • double sum(const deque<double> &lst){ • double s = 0; deque<double>::const_iterator c; for (c=lst.begin(); c != lst.end(); ++c) s += *c ; return s;} 5/8/2002 14

  15. Typical Container Algorithm (2 of 2) • deque (double ended queue) container is traversed using a const_iterator • Iterator c is dereferenced to obtain each stored value in turn • Algorithm will work with all containers and all types that have operator+=() defined 5/8/2002 15

  16. Containers with Iterators (1 of 2) • #include <iostream.h> • #include <deque> • using namespace std; • template<class itr> //common stl use of iterator • double sum(itr b, itr e) • { • double s = 0.0; • for( ; b != e; ++b) • s = s + *b; • return s; • } 5/8/2002 16

  17. Containers with Iterators (2 of 2) • //more general abstraction works on vectors • //arrays indeed any container with iterator • int main() • { • //initialize to 10 2.5's • deque< double > data(10, 2.5); • double d[5] = {1.0, 2.5, 3.3, 8.8, 9}; • cout << sum(data.begin(), data.end()) • << endl; • cout << sum(d, d + 5)<< endl; • cout << endl; • } 5/8/2002 17

  18. Comments on Containers with Iterators • Relies on use of iterator range • Most standard idiom • Works with arrays as well using addresses • Will be like an STL numeric algorithm • Note use of constructor for initialization 5/8/2002 18

  19. set multiset map multimap Associative Containers • Key based accessible elements • Ordering relation Compare • Comparison object for the associative container 5/8/2002 19

  20. Associative Container Program (1 of 2) • int main(){ map<string, int, less<string> > name_age; • //key, value stored, ordering • name_age["Pohl,Laura"] = 7; name_age["Dolsberry,Betty"] = 39; cout << "Laura is " << name_age["Pohl,Laura"] << " years old." << endl;} 5/8/2002 20

  21. Associative Container Program (2 of 2) • map name_age is an associative array where key is a string type • Compare object is less<string> 5/8/2002 21

  22. Additional Associative Definitions ASSOC::key_type retrieval key type ASSOC::key_compare comparison object type ASSOC::value_compare type for comparing ASSOC::value_type 5/8/2002 22

  23. Associative Insert & Erase Functions (1 of 2) c_unique.insert(t) Insert t, if no existing key t c_eq.insert(w_it, t) Insert t, return position w_it c.insert(w_it, t) Insert t with starting position w_it for search (fails on sets and maps if key value already exists) c(b_it, e_t) Inserts element range c.erase(k) Erases elements with key k,return # erased elements c.erase(w_it) Erases pointed to element c.erase(b_it, e_t) Erases range of elements 5/8/2002 23

  24. Associative Member Functions c.find(k) Returns iterator to element having key k, otherwise end c.count(k) Returns # of elements with k c.lower_bound(k) Returns iterator to first element having value greater than or equal to k c.upper_bound(k) Returns iterator to first element having value greater than k c.equal_range(k) Returns iterator pair for lower_bound & upper_bound 5/8/2002 24

  25. stack queue priority_queue Container Adapter Classes • Modify existing containers to produce different public behaviors based on existing implementation • stack can be adapted from vector, list and deque • Last in first out data structure • Supports back, push_back and pop_back 5/8/2002 25

  26. Adapted Stack Functions void push(const value_type& v)Place v on stack void pop() Remove top element value_type& top() const Return top element bool empty() constReturns true if stack empty size_type size() const Returns # of elements operator== and operator< Equality and less supported 5/8/2002 26

  27. vector list deque Sequence Containers • Sequence containers have a sequence of accessible elements • C++ array type can also be treated as a sequence container 5/8/2002 27

  28. Sequence Container Program (1 of 3) • //inserting a vector into a dequeint main(){ int data[5] = { 6, 8, 7, 6, 5 }; vector<int> v(5, 6); //5 element vect deque<int> d(data, data + 5); deque<int>::iterator dq_it; 5/8/2002 28

  29. Sequence Container Program (2 of 3) • cout << "\n Deque values\n\n"; for (dq_it = d.begin(); dq_it != d.end(); ++dq_it) cout << *dq_it << '\t'; //print:6 8 7 6 5 cout << endl; d.insert(d.begin(), v.begin(), v.end()); for (dq_it = d.begin(); dq_it != d.end(); dq_it++) cout << *dq_it << '\t'; • //print:6 6 6 6 6 6 8 7 6 5} 5/8/2002 29

  30. Sequence Container Program (3 of 3) • 5 element vector v initialized with value 6 • deque d initialized with values taken from array data • insert() member function places v values in specified range v.begin() to v.end() at location d.begin() 5/8/2002 30

  31. Additional Sequence Members in SEQ SEQ::SEQ(n, v)n elements of value v SEQ::SEQ(b_it, e_it) start at b_it and go to e_it - 1 c.insert(w_it, v)insert v before w_it c.insert(w_it, v, n) insert n copies of v before w_it c.insert(w_it, b_it, insert b_it to e_it e_it) before w_it c.erase(w_it) erases element at w_it c.erase(b_it, e_it)erase b_it to e_it 5/8/2002 31

  32. Adapted Containers (1 of 2) • Include Stack, Queue, Priority Queue • Stack adapted from vector, list, or deque • Stack adapted from user defined container with operations empty, size, push_back, pop_back, and back operations • stack < list < double > > stk • Supports stack operations 5/8/2002 32

  33. Adapted Containers (2 of 2) • Queue adapted from list or deque but not vector • needs push_back, pop_front • Priority queue can be adapted from vector or deque • need random access 5/8/2002 33

  34. Stack Adapted from Vector (1 of 2) • int main(){ stack<vector<string> > str_stack; • string quote[3] = {"The wheel that squeaks the loudest\n", "Is the one that gets the grease\n", "Josh Billings\n" }; 5/8/2002 34

  35. Stack Adapted from Vector (2 of 2) • for (int i =0; i < 3; ++i) str_stack.push(quote[i]); while (!str_stack.empty()) { cout << str_stack.top(); str_stack.pop(); }} 5/8/2002 35

  36. forward • input • output Iterators • Means for navigating data structure • Iterators in STL are pointer-style objects used to return with data stored in containers • Iterators in STL come in 5 categories random access bidirectional 5/8/2002 36

  37. Iterators and Containers and Algorithms • Algorithm may not support all iterator categories • List will not support random access iterator but will support bidirectional iterators • Sorting requires random access but finding requires only input iterator • Vector containers allow random access 5/8/2002 37

  38. Input Iterator • Equality, dereferencing, autoincrement • One pass algorithms read values in one direction • Conforms to following properties where Iter has first and first != lastfirst++//accesses next element • *first defined and can be used to compare, increment, dereference and assign elements of type Iter • Special case istream_iterator 5/8/2002 38

  39. istream_iterator for Reading from Streams • int main(){ int d[5]; • cout << "\nEnter integers: "; istream_iterator<int,ptrdiff_t> in(cin); for (int i = 0; i < 5; ++i) { d[i] = *in++; cout << "\nd[" << i << "] = " << d[i] << endl; }} 5/8/2002 39

  40. Output Iterator • Supports dereferencing restricted to left hand side of assignment and autoincrement • One pass algorithms write values in one direction • If Iter is output iterator type withIter ptr • *ptr can be on the left hand side of assignment • ptr++ is defined 5/8/2002 40

  41. The output is all run together! Special case ostream_iterator Use the char* \t delimiter and a tab character will be issued to cout after each int value written 5/8/2002 41

  42. The ostream_iterator for Writing to Streams • int main(){ int d[5] = {2, 3, 5, 7, 11}; //primes ostream_iterator<int> out(cout, "\t"); for (int i = 0; i < 5; ++i) *out = d[i] ;} 5/8/2002 42

  43. Forward Iterator • Supports all input/ output operations • Supports unrestricted use of assignment • Allows position within data structure retained from pass to pass • One directional multi-pass algorithms • Able to save position and restart an algorithm from that position 5/8/2002 43

  44. Bidirectional Iterator • Supports all forward iterator operations • Supports both autoincrement and autodecrement • General bidirectional multi-pass algorithms 5/8/2002 44

  45. Random Access Iterators Any location is accessible in constant time 5/8/2002 45

  46. Random Access Iterators Support • All bidirectional operations • General bidirectional multi-pass algorithms • Address arithmetic operations & comparison • ptr += n and ptr -= n • ptr1 - ptr2 5/8/2002 46

  47. STL Algorithms Library • Sorting algorithms • Non-mutating sequence algorithms • Mutating sequence algorithms • Numerical algorithms • Generally use iterators to access containers instantiated on given type • Resulting code can be competitive in efficiency with special purpose codes 5/8/2002 47

  48. Sorting Algorithms • General sorting, merge, heap, permutation, lexicographic comparison, binary search and selected other like operations • Algorithms have versions that use either operator<() or Compare object 5/8/2002 48

  49. Using sort() for In-Memory quicksort • const int N = 5;int main(){ int d[N], i, *e = d + N; for (i = 0; i < N; ++i) d[i] = rand(); sort(d, e); for (i = 0; i < N; ++i) cout << d[i] << '\t';} 5/8/2002 49

  50. Sorting Algorithm Prototypes (1 of 6) • template<class RandAcc>void sort(RandAcc b, RandAcc e); • Quicksort algorithm over elements b to e • template<class RandAcc>void stable_sort(RandAcc b, RandAcc e); • Stable sorting algorithm over elements b to e • Elements remain in their relative same position 5/8/2002 50

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