Chapter 14 Introduction to the Standard Template Library

§14.1 Introduction

§14.2 Containers

§14.3 Iterators

§14.4 Algorithms

§14.5 Function Objects

§14.1 Introduction

Standard Template Library (STL) 标准模板库 A software library included in the C++ Standard Library

Purpose To standardize commonly used components

History Originally developed by Alexander Stepanov in 1980s Accepted as part of C++ standard in Feb. 1994

2

Components of STL

Containers（容器） A container object, such as vector, used to store a

collection of data, often referred to as elements Algorithms（算法）

Functions to manipulate data such as sorting, searching, and comparing elements.

Most of them use iterators to access the elements in the container.

Iterators（迭代器） Objects that facilitate traversing through the elements in

a container Like built-in pointers that provide a convenient way to

access and manipulate the elements in a container

3

Components of STL

4

Algorithm 3Algorithm 3

Algorithm 2Algorithm 2Algorithm 1Algorithm 1

Container

Object 1 Object 2

Object 3

Iterator 3

Iterator 2Iterator 1

§14.2 Containers

5

ContainersContainers

•vector•deque•list

Sequence containers

•set•multiset•map•multimap

Associative containers

• stack• queue• priority_queue

Derived containers

linear data structures

Non-linear (tree) containers Suitable for searching

Constrained versions of sequence containers

Sequence Containers

Represent linear data structures Three sequence containers

vector 向量 , list 表 , and deque 双端队列 Differ only in performance

6

Element 0Element 0

iterator

Begin() end()

Element 1Element 1 Element 2Element 2Last

ElementLast

Element

int values[] = {1, 2, 3, 4 }; list<int> intList(values, values + 4);

Sequence Containers

7

Container Random access

Insertion or deletion in the

middle

Insertion or deletion at the

ends

vector Fast Slow Fast at back

list Slow Fast Fast at front

deque Fast SlowFast at both the ends

Associative Containers

Represent non-linear data structures (tree) Elements are sorted by keys

E.g. the name of student objects Suitable for searching via keys Set/Multiset: set of items Map/Multimap: set of item pairs

8

int values[] = {3, 5, 1, 7, 2, 2}; set<int> set1(values, values + 6);

map<int, string> map1; map1.insert(map<int, string>::value_type(100, "John Smith"));

Derived Containers

Containers adapted from the sequence containers For handling special cases

Programmer can choose an appropriate sequence container for a derived containers

9

Headerfile

Features Impl. struct.

stack <stack> Last-In-First-Out deque*, list, vector

queue <queue> First-In-First-Out deque*, list

priority_queue <queue> Largest-In-First-Out vector*, deque

*: default one

stack<int, vector<int> > stack2;

Containers supported by the STL

Container Description Header File

Iterator

vector A dynamic array. Allows insertions and deletion at back. Permits direct access to any element

<vector> Random access 

list A bidirectional, linear list. Allows insertions and deletions anywhere.

<list> Bidirectional 

deque A double-ended queue. Allows insertions and deletions at both the ends. Permits direct access to any element.

<deque> Random access 

set An associate container for storing unique sets. Allows rapid lookup. (No duplicates allowed)

<set> Bidirectional 

multiset An associate container for sorting non-unique sets. (Duplicates allowed)

<set> Bidirectional 

10

Containers supported by the STL

Container Description Header File

Iterator

map An associate container for storing unique key/value pairs. Each key is associated with only one value (One-to-one mapping). Allows key-based lookup.

<map> Bidirectional 

multimap An associate container for storing key/value pairs with one key may be associated with more than one value (one-to-many mapping). Allows key-based lookup.

<map> Bidirectional 

stack A standard stack. Last-in-first-out(LIFO). <stack> No iterator 

queue A standard queue. First-in-first-out(FIFO). <queue> No iterator 

priority-queue

A priority queue. The first element out is always the highest priority element.

<queue> No iterator 

11

Common Functions in All Containers

12

Functions Description

non-arg constructor Constructs an empty container.

constructor with args In addition to the non-arg constructor, every container

has several constructors with args.

copy constructor Creates a container by copying the elements from an

existing container of the same type.

destructor Performs cleanup after the container is destroyed.

empty() Returns true if there are no elements in the container.

size() Returns the number of elements in the container.

operator= Copies one container to another.

Relational operators The elements in the two containers are compared

(<, <=, >, >=, sequentially to determine the relation.

==, and !=)

Common Functions in Sequence/Associative Containers

13

Functions Description

c1.swap(c2) Swap the elements of two containers c1 and c2.

c.max_size() Returns the maximum number of elements a container can hold.

c.clear() Erases all the elements from the container.

c.begin() Returns an iterator to the first element in the container.

c.end() Returns an iterator that refers to the next position after the

end of the container.

c.rbegin() Returns an iterator to the last element in the container for

processing the elements in reverse order.

c.rend() Returns an iterator that refers to the position before the

first element in the container

c.erase(beg, end) Erases the elements in the container from beg to end-1. Bothe

beg and end are iterators.

Common Functions in Sequence Container

14

Functions Description

assign(n, elem) Assign n copies of the specified element in the container.

assign(beg, end) Assign the elements in the range from iterator

beg to iterator end.

push_back(elem) Appends an element in the container.

pop_back() Removes the last element from the container.

front() Returns the reference of the first element.

back() Returns the reference of the last element.

insert(position, elem) Inserts an element at the specified iterator.

Common Functions in Associative Containers

15

Functions Description

find(key) Returns an iterator that points to the element with

the specified key in the container.

lower_bound(key) Returns an iterator that points to the first

element with the specified key in the container.

upper_bound(key) Returns an iterator that points to the next element

after the last element with the specified key in

the container.

count(key) Returns the number of occurrences of the element

with the specified key in the container.

§14.3 Iterators

Iterators are objects to facilitate traversing through the elements in a container

A iterator is like a built-in pointer that can manipulate the elements in a container

16

random access

bidirectional

forward

input output

Iterators and Characteristics

Iterator Access method

Direction of movement

I/O capability Remark

Input Linear Forward only Read only Cannot be saved

Output Linear Forward only Write only Cannot be saved

Forward Linear Forward only Read/Write Can be saved

Bidirectional Linear Forward and backward

Read/Write Can be saved

Random Random Forward and backward

Read/Write Can be saved

17

Iterator Operations

Iterator Element access

Read Write Increment operation

Comparison

Input -> V=*p ++ ==,!=

Output V=*p *p=v ++ ==,!=

Forward -> V=*p *p=v ++ ==,!=

Bidirectional -> V=*p *p=v ++,-- ==,!=

Random ->,[] V=*p *p=v ++, --, _, -, +=, -=

==,!=,<,>,<=,>=

18

Iterator Types Supported by Containers

19

STL Container Type of Iterators Supported

vector random access iterators deque random access iterators

list bidirectional iterators

set bidirectional iterators

multiset bidirectional iterators

map bidirectional iterators

multimap bidirectional iterators

stack no iterator support

queue no iterator support

priority_queue no iterator support

Iterator Demo

20

vector<int> intVector; intVector.push_back(10); intVector.push_back(20); intVector.push_back(30); intVector.push_back(40); intVector.push_back(50); intVector.push_back(60);

vector<int>::iterator p1 = intVector.begin(); for (; p1 != intVector.end(); p1++){ cout << *p1 << " "; } cout << endl << *(--p1) << endl; cout << *(p1 - 3) << endl; cout << p1[-3] << endl; *p1 = 1234; cout << *p1 << endl;

IteratorDemoIteratorDemo Run

§14.4 Algorithms

More than sixty algorithms in STL Five groups

Retrieve or non-mutating Algorithms Mutating Algorithms Sorting Algorithms Set Algorithms Relational Algorithms

21

The copy Algorithm

22

template <typename InputIterator, typename OutputIterator>copy(InputIterator beg, InputIterator end, OutputIterator targetPostition)

int values[] = {1,2,3,4,5,6};vector<int> intVector(5);list<int> intList(5);

copy(values+2, values+4, intVector.begin());copy(values, values+5, intList.begin());

#include <algorithm>#include <vector>#include <list>#include <iterator>

Copy to Output Stream

23

intVector.insert(intVector.begin(), 747);

ostream_iterator<int> output(cout, " ");

cout<<"\nAfter the insertion funciton, intVector: ";copy(intVector.begin(), intVector.end(), output);

The copy Demo

24

After initial copy intVector: 3 4 0 0 0After initial copy intList: 1 2 3 4 5After the insertion function, intVector: 747 3 4 0 0 0After the copy function, intList: 747 3 4 0 5

int values[] = {1,2,3,4,5,6};vector<int> intVector(5);list<int> intList(5);

copy(values+2, values+4, intVector.begin());copy(values, values+5, intList.begin());intVector.insert(intVector.begin(), 747);copy(intVector.begin(), intVector.begin()+4, intList.begin());

int values[] = {1,2,3,4,5}vector<int> intVector;copy(values+2, values+4, intVector.begin());

Caution

The target container in copying must contains enough elements to store the values from the source container

25

“sort” and “binary_search”

26

template <typename RandomAccessIterator>void sort(RandomAccessIterator beg, RandomAccessIterator end)

template <typename RandomAccessIterator, typename relationalOperator>void sort(RandomAccessIterator beg, RandomAccessIterator end, relationalOperator op)

template <typename ForwardIterator, typename T>bool binary_search(ForwardIterator beg, ForwardIterator end, const T &value)

template <typename ForwardIterator, typename T, typename strickWeakOrdering>

bool binary_search(ForwardIterator beg, ForwardIterator end, const T &value, strickWeakOrdering op)

SortDemoSortDemo Run

Demo of sort, binary_search

27

int array1[] = {1, 7, 3, 4, 3, 3, 1, 2};

sort(array1, array1 + 8);

binary_search(array1, array1 + 8, 4)

sort(array1, array1 + 8, greater_equal<int>());

binary_search(array1, array1 + 8, 4, greater_equal<int>())

A function operator!A function operator!

§14.5 Function Objects Object can be used as a function

“function” “object” Passing a function as a parameter In <functional> header

28

int main(){int x[] = {10,50,30,40,20};int y[] = {70,90,60,80};sort(x,x+5,greater<int>());sort(y,y+4);for (int i=0;i<5;i++) cout<<x[i]<<" "; cout<<"\

n";for (int j=0;j<4;j++) cout<<y[j]<<" "; cout<<"\

n";int z[9];merge(x,x+5,y,y+4,z);for (int i=0;i<9;i++) cout<<z[i]<<" "; cout<<"\n";

}

Functors in <functional>

29

STL function object type STL function object type

equal_to<T> relational

not_equal_to<T> relational

greater<T> relational

greater_equal<T> relational

less<T> relational

less_equal<T> relational

logical_and<T> logical

logical_not<T> logical

logical_or<T> logical

plus<T> arithmetic

minus<T> arithmetic

multiplies<T> arithmetic

divides<T> arithmetic

modulus<T> arithmetic

negate<T> arithmetic

Customized Function Objects By defining member function operator() in a class

30

class My { public: int operator()(int a) {return a;} } ;My mo; int x = mo(0); template <typename T> class greater : binary_function <T,T,bool> {public: bool operator() (const T& x, const T& y) const{return x>y;}};

class BiggerThan{public: const int testValue; BiggerThan(int x) : testValue(x) { } bool operator()(int val) const { return val > testValue; }};

int my[] = {1, 7, 3, 4, 3, 3, 1, 2};sort(my, my + 8, Mygreater<int>());BiggerThan bt(10);cout<<bt(11)<<" "<<bt(9)<<endl;My m;cout<<m(4)<<endl;

1 04

A Summary

Concepts STL, Container, Iterator, Algorithm Three types of containers Function, Operation, Algorithm Functional object

Features of different containers Main functions of containers Features of STL algorithm Use of functional object

31