Oct 20, 2009

STL Containers

Dr. Partha Pratim DasInterra Systems (India) Pvt. Ltd.

Generalizing Data Structures

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Agenda

• STL Components– Containers– Iterators– Algorithms

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STL Components

Why & HowWhy & How

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STL Components

• STL is a cooperation of Components

• Key Components– Containers– Iterators– Algorithms

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Containers

• Manage collection of objects of a kind

• Every Container Type reflect a conglomeration of requirements

• May be implemented as – Arrays– Linked Lists– Special Keys for every Element

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Iterators

• Used to step through elements of collections of objects

• Collections may be – Containers or

– Subsets of Containers

• Offers a small yet common interface for any arbitrary container type

• This works independent of the Internal Structure• Example: Iterator steps to the next element.

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Algorithms

• Used to process elements of collections• Examples:

– Search– Sort– Modify– Use

• Algorithms use Iterators• Algorithms can call user-defined functions

(functors)

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Concept of STL

• Separation of Data and Operations– Data Managed by Container Classes– Operations Defined by Configurable

Algorithms– Iterators Glue between these Components

• Contradicts OOP – through separation

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Basic Model

• Algorithmssort, find, search, copy, …

• Containers vector, list, map, hash_map, …

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iterators

• Separation of concerns– Algorithms manipulate

data, but don’t know about containers

– Containers store data, but don’t know about algorithms

– Algorithms and containers interact through iterators

• Each container has its own iterator types

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Containers

Basic StuffBasic Stuff

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Types of Containers

• Sequence Containers– Ordered Collection– Every element has a certain position– Position depends on time and place of Insertion– Position is independent of value– Predefined Sequence Containers are:

• vector

• deque

• list

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Types of Containers

• Associative Containers– Sorted Collection– Position of an element depends on its value and

a certain sorting criterion– Order of Insertion is immaterial– Predefined Associative Containers are:

• set• multiset• map• multimap

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Types of Containers

• Container Adaptors– Meets special needs– Implemented using fundamental containers– Predefined Container Adaptors are:

• stack

• queue

• Priority queue

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Common Containers Abilities

• Constructor– Default: ContType c– Copy: ContType c1(c2)– Initialize with a Range: ContType c(beg, end)

• Destructor: ~ContType c

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Common Containers Abilities

• Size Operations– c.size(): Actual number of elements– c.empty(): Whether the container is empty– c.max_size(): Maximum number of elements

possible

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Common Containers Abilities

• Comparison Operators:– Operators: ==, !=, <, <=, >, >=– Both containers must have the same type– Two containers are equal if their elements are

equal and have the same order– To check if a container is less than another, a

lexicographic comparison is done

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Common Containers Abilities

• Assignments and swap()– c1 = c2:

• Copy all elements of the source container and remove all old elements of the destination container

• Linear Complexity - expensive

– c1.swap(c2) / swap(c1, c2)• Use when containers have the same type and source

is no longer used• Swaps some internal pointers that refer to the data

(elements, allocator, sorting criterion)• Constant Complexity

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Common Containers Abilities

• Iterator Functions– c.begin():

• Iterator for first element

– c.end(): • Iterator for last element

– c.rbegin(): • Reverse Iterator for first element

– c.rend(): • Reverse Iterator for last element

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Common Containers Abilities

• Manipulators– c.insert(pos, elem):

• Insert a copy of elem at pos

– c.erase(beg, end): • Remove all elements in range [beg, end)

– c.clear(): • Remove all elements – makes the container empty

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Sequence Container: vector

• Vector models a dynamic array

• #include <vector>

• Special Operations– Element Access

• c.at(idx) / c[idx]

• c.front() / c.end()

– Insert / Remove at the back• c.push_back(elem)

• c.pop_back()

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Sequence Container: vector

• Remove the first element with a value

std::vector<Elem> coll;

std::vector<Elem>::iterator pos;

pos = find(coll.begin(), coll.end(), val);if (pos != coll.end()) {

coll.erase(pos);}

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Sequence Container: deque (“deck”)

• Similar to Vector– Manages elements with Dynamic Array

– Provides Random Access

– Almost same interface as Vector

– Deque is open at both ends.

• #include <deque>• Special Operations

– Insert / Remove• c.push_back(elem) / c.pop_back()

• c.push_front(elem) / c.pop_front()

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Sequence Container: list

• Manages elements in a doubly linked list

• #include <list>

• Element Access– front() / back()

• Insert / Remove– push_ / pop_ at both ends

• Splice / Sort / Merge / Reverse

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Sequence Container: strings

• C++ string classes as containers– basic_string<>– string– wstring

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Sequence Container: Ordinary Array

• Has static or dynamic size

• Not STL Containers– No size()– No empty()

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Associative Container: set / multiset

• Sorts the elements according to a sorting criterion

• Sets do not allow duplicates

• Multisets allow duplicates

• #include <set>

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Associative Container: map / multimap

• Manage key/value pairs as elements

• Sorts the elements according to a sorting criterion that is used for the actual key

• Maps do not allow duplicates

• Multimaps allow duplicates

• #include <map>

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Container Adapter: stack

• #include <stack>

• Core Operations– push()– top()– pop()

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Container Adapter: queue

• #include <queue>

• Core Operations– push()– front()– pop()– back()

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Container Adapter: priority queue

• priority_queue implements a queue from which elements are read according to their priority

• #include <queue>

• Core Operations– push()– top()– pop()

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Iterators

Basic StuffBasic Stuff

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Iterator Interface

• Can iterate (navigate) over elements• All or part of the elements in an STL

container• Fundamental Operations

– operator*– operator++– operator==– operator!=– operator=

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Container Interface for Iterators

• Fundamental Container Operations for Iterators– begin()– end()

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Basic Iterator Model• A pair of iterators define a sequence

– The beginning (points to the first element – if any)– The end (points to the one-beyond-the-last element)

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…

begin: end:

• An iterator is a type that supports the “iterator operations”• ++ Go to next element

• * Get value

• == Does this iterator point to the same element as that iterator?

• Some iterators support more operations (e.g. --, +, and [ ])

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Use of Iterators std::list<char> coll;

std::list<char>::const_iterator pos;

for(pos = coll.begin(); pos != coll.end(); ++pos)

{

cout << *pos << ‘ ‘;

}

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Iterator Categories

• Bidirectional Iterators

• Random Access Iterators

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Iterator Adaptors

• Insert Iterators

• Stream Iterators

• Reverse Iterators

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Algorithms

Basic StuffBasic Stuff

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Algorithm Overview

• STL provides several standard algorithms• Algorithms are not member functions of

containers• Algorithms are global functions that operate with

iterators• Algorithms can operate on various types• Algorithms do not belong to Object Oriented

Paradigm, they belong to Generic Programming Paradigm

• #include <algorithm>

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References

• The C++ Standard Library: A Tutorial and Reference

– Nicolai M. Josuttis

• Effective STL– Scott Meyers

• C++ Template Metaprogramming– Abrahams & Gurtovoy

• C++ Templates: The Complete Guide – David Vandevoorde & Nicolai M. Josuttis

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Thank You