1 stl containers copyright kip irvine, 2003. all rights reserved. only students enrolled in a class...

1

STL ContainersSTL Containers

Copyright Kip Irvine, 2003. All rights reserved. Only students enrolled in a class at Florida International University may copy or print the contents of this slide show.

Last update: 3/30/2003

Copyright 2003, Kip R.Irvine 2

Standard Template Library (STL)Standard Template Library (STL)

Created by Alexander Stepanov and Meng Lee at Hewlett-Packard

Key components: containers, iterators, algorithms Helps you avoid having to re-invent standard

container implementation code Design choice: generic classes chosen for runtime

efficiency• more efficient than object-based containers that use

polymorphism


Standard Template Library (STL)Standard Template Library (STL)

Recently incorporated into the Standard C++ Library STL Programmers' Guide available at:

• http://www.sgi.com/tech/stl• Latest release: 3.3, June 2000.

http://www.sgi.com/tech/stl


Types of ContainersTypes of Containers

Sequence containers• vector• deque• list

Associative containers• set, multiset• map, multimap

Container adapters• stack• queue• priority_queue


Required HeadersRequired Headers

Class name same as header:• <vector>, <list>, <deque>, <stack>, <bitset>

Also:• <queue> queue, priority_queue• <set> set, multiset• <map> map, multimap


Error HandlingError Handling

Exceptions are never thrown by STL classes In fact, exceptions and templates don't mix Very little error checking exists in STL classes


Common TypedefsCommon Typedefs

value_type• type of element stored in the container

reference, const_reference• reference to type of element stored in the container

pointer• pointer to the type of element stored in the container

iterator, const_iterator• a forward iterator that points to the type of element stored in

the container reverse_iterator, const_reverse_iterator

• a reverse iterator that points to the type of element stored in the container


Common typedefs in STL Common typedefs in STL (cont)(cont)

difference_type• type of the result of subtracting two iterators

size_type• type used to count items in a container, and index through a

sequence container


Common Member FunctionsCommon Member Functions

default constructor, copy constructor, destructor empty max_size

• max number of elements for a container size

• number of elements currently in the container operator =

• assign one container to another overloaded <, <=, >, >=, ==, != swap


Common Member FunctionsCommon Member Functions

begin returns an iterator (-> first element) end returns an iterator (-> after last

element) erase erase 1 or more elements clear erase all elements rbegin returns reverse_iterator rend returns reverse_iterator


Element Types for ContainersElement Types for Containers

Must have correct copy semantics• bitwise default, or• overload the assignment ( = ) operator and copy

constructor Provide operator < and operator ==


Types of IteratorsTypes of Iterators

Input Iterator (InIt)• Used to read an element from a container• Moves only in forward direction, one element at a time• Cannot pass through a sequence twice

Output Iterator (OutIt)• Used to write an element to a container• Moves only in forward direction, one element at a time• Cannot pass through a sequence twice

Each iterator's capabilities are a superset of the previously listed iterators.


Types of IteratorsTypes of Iterators (cont) (cont)

Forward Iterator (FwdIt)• reads and writes in forward direction only• retains its position in the container

Bidirectional Iterator (BidIt)• reads and writes in both directions• retains its position in the container

Random-Access Iterator (RadIt)• reads and writes in randomly accessed positions• permits pointer arithmetic

Each iterator's capabilities are a superset of the previously listed iterators.


Iterator Support, by ContainerIterator Support, by Container

stack, queue, priority_queue: no iterators list, set, multiset, map, multimap: bidirectional vector, deque: random


Invalidating IteratorsInvalidating Iterators

Some, but not all operations on containers invalidate iterators• result: iterator can be stale• remember that iterators are basically pointers

Examples:• list.push_back( ) does not invalidate iterators• vector.push_back( ) invalidates all iterators• list.erase( ) invalidates only iterators that pointed to the

deleted elements• check the documentation for each method!


Sequence ContainersSequence Containers


vectorvector Container Container

sequence container with contiguous memory locations

permits direct access to any member via [ ] or at( ) automatically doubles its allocation when current size

is exceeded insertion and deletion only permitted at the tail supports random-access iterators

• all lesser iterators also


Common Common vectorvector Functions Functions

push_back, pop_back• add to end, remove from end

size• current number of elements

capacity• storage allocation size

begin, end• return iterator and const_iterator

rbegin, rend• return reverse_iterator and const_reverse_iterator

front, back• return first and last elements


Common Common vectorvector Functions Functions

at( ) operator [ ]

(also found in deque)


listlist Sequence Container Sequence Container

efficient insertion and deletion at any location• deque is more efficient if insertions and deletions are at the

ends of the container implemented as doubly-linked list

• supports bidirectional iterators does not support

• at( ) or operator [ ]


listlist Operations Operations

operations not found in vectors:

void splice( iterator iter, list & X )

• removes values from list X and inserts them into the current list in the position immediately before position iter

void push_front( const T & X )

• inserts element X at the front of the listvoid pop_front( )

• removes one element from the front of the listvoid remove( const T& x )

• removes all elements found to be equal to X


Unique Unique listlist Operations Operations

void unique()Removes from the current list every element that is equal to its preceding element

void merge( list & other )Removes from the list other and insert them in sorted order into the current list

void reverse()Reverses the order of elements in the current list

void sort()Sorts the list in ascending order by automatically calling the < operator function to compare pairs of elements

void sort( greater<T> pred )Sorts the list in descending order by automatically calling the < operator function to compare pairs of elements


Creating a Creating a listlist

list<int> scores;

scores.push_back( 20 );

scores.push_front( 10 );

scores.pop_front( );

scores.remove( 20 ); // removes "20"

cout << "size: " << scores.size( ) << endl;

List of lists containing strings:list< list<string> > L;

Disable Microsoft VS 6.0 warning message that appears when templates contain strings:

#ifdef _DEBUG

#pragma warning( disable : 4786 )

#endif


Printing a Printing a listlist

template < class T >

void print( const list<T> & aList )

{

if ( aList.empty() )

cout << "List is empty";

else

{

list<T>::const_iterator I = aList.begin( );

for( ; I != aList.end( ); I++ )

cout << *I << ", ";

cout << endl;

}

}


Removing Removing listlist Duplicates Duplicates

list<int> scores;





scores.unique( );

print( scores ); // 10, 20, 30


List of ListsList of Lists

typedef list<string> stringList;

stringList s;

s.push_back( "Dan" );

s.push_back( "Bill" );

s.push_back( "Anne" );

// a list containing lists of strings

list<stringList> L;

L.push_back( s );


Associative ContainersAssociative Containers


Associative ContainersAssociative Containers

keys are always kept in sorted order• iterator always traverses in sort order

set – single key values• equivalent to Java's TreeSet

multiset – duplicate keys allowed map – contains pairs (key, value)

• key is unique• equivalent to Java's TreeMap

multimap• key need not be unique


Sets: Three Ways to Insert ItemsSets: Three Ways to Insert Items

insert single value, returning an iteratoriterator insert( const value_type & x);

start searching for insert point after iterator it:iterator insert( iterator it,

const value_type & x );

insert sequence of elements in the range [first, last):void insert( const value_type * first,

const value_type * last );


Examples: Inserting and FindingExamples: Inserting and Finding

Create a multiset and insert single values:multiset<int> B;

B.insert( 30 );

B.insert( 20 );

Insert an array:const int SIZE = 5;

int array1[SIZE] = { 10,20,30,30,40 };

B.insert( array1, array1 + SIZE );

Find a value:multiset<int>::const_iterator I = B.find( 30 );


Using Using typedeftypedef

Use typedef to simplify type definitions:

typedef multiset<int> msetInt;

.

msetInt A;

typedef multiset<int>::const_iterator msetIter;

.

msetIter = A.insert( 30 );


Printing a MultisetPrinting a Multiset

template < class T >

void print( const multiset<T> & aSet )

{

if ( aSet.empty() )

cout << "Set is empty";

else

{

multiset<T>::const_iterator I = aSet.begin( );

for( ; I != aSet.end( ); I++ )

cout << *I << ", ";

}

}


setset Associative Container Associative Container

keys are unique• attempt to insert duplicate key is ignored

same functions as multiset


mapmap Associative Container Associative Container

unique keys and their associated values each key is mapped to a single value

• values do not have to be unique fast storage and retrieval sorted in order according to keys Iterators point to pair<key,value>

• fields named first, second values can be inserted using [ ] operator

see: mapdemo.cpp


Function ObjectsFunction Objects

template class that contains a function• the function can be used in the same way as operator ( )

make STL more flexible• permit sorting on your own criteria

predefined objects in STL:• divides< T >• equal_to< T >• greater< T >• greater_equal< T >• less< T >• etc.


Function Object ExampleFunction Object Example

Default comparison of STL container objects when sorting uses the < operator:

template<typename T>

class less {

public:

bool operator()(const T & x, const T & y) const

{

return x < y;

}

};


Function Object ExampleFunction Object Example

When you declare a set, you have the option of specifying a function object that will determine the positions where new elements are inserted.

Example: set of strings named myStringSet:

set<string, less<string> > myStringSet;


Binary Function ExampleBinary Function Example

Base class binary_function defines overloaded ( ) operator with two arguments.

This function object squares a value and adds it to a total:

template< typename T >class SumSquaresClass :public binary_function<T, T, T>{public:

const T operator( )( const T & total, const T & value ){

return total + value * value; }

};


Binary Function ExampleBinary Function Example (cont) (cont)

accumulate( first, last, startVal, pred )

The STL defines an accumulate function that accumulates a sum over a collection. • the optional pred parameter can be a function or a function

object

vector<int> v;

. . .

int sum = accumulate( v.begin( ), v.end( ), 0,

SumSquaresClass<int>() );


Optional InformationOptional Information


dequedeque sequence container sequence container

pronounced "deck" provides benefits of vector and list in the same

container• rapid indexed access (like vector)• efficient insertion & deletion at its ends (like list)• supports random-access iterators• often used for FIFO queue• noncontiguous memory layout


CommonCommon deque deque operations operations

push_back( ) push_front( ) pop_back( ) pop_front( ) size( ) operator [ ] at( )


dequedeque Example #1 Example #1

Create a deque containing pointers to strings:

deque<Message *> mque;

mque.push_back( new Message( "John", "How are you?" ));

mque.push_back( new Message( "Sam", "What's happening?" ));

mque.push_back( new Message( "Anne", "What's for dinner?" ));

mque.push_back( new Message( "Bill", "Let's go surfing!" ));


dequedeque Example #1 Example #1

Serve all messages from the front of the queue until the queue is empty:

while( mque.size( ) > 0 )

{

cout << **(mque.begin( )) << endl;

mque.pop_front( );

}

see dequeDemo.cpp


The EndThe End

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