STL Containers
Last update: 3/30/2003
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.
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Standard Template Library (STL)
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
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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
Copyright 2003, Kip R.Irvine
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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.
Copyright 2003, Kip R.Irvine
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Types of Containers
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Sequence containers
• vector
• deque
• list
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Associative containers
• set, multiset
• map, multimap
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Container adapters
• stack
• queue
• priority_queue
Copyright 2003, Kip R.Irvine
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Required Headers

Class name same as header:
• <vector>, <list>, <deque>, <stack>, <bitset>
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Also:
• <queue>
• <set>
• <map>
queue, priority_queue
set, multiset
map, multimap
Copyright 2003, Kip R.Irvine
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Error Handling
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Exceptions are never thrown by STL classes
In fact, exceptions and templates don't mix
Very little error checking exists in STL classes
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Common Typedefs

value_type
• type of element stored in the container
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reference, const_reference
• reference to type of element stored in the container
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pointer
• pointer to the type of element stored in the container
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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
Copyright 2003, Kip R.Irvine
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Common typedefs in STL

(cont)
difference_type
• type of the result of subtracting two iterators
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size_type
• type used to count items in a container, and index through a
sequence container
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Common Member Functions
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default constructor, copy constructor, destructor
empty
max_size
• max number of elements for a container
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size
• number of elements currently in the container
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operator =
• assign one container to another
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overloaded <, <=, >, >=, ==, !=
swap
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Common Member Functions
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begin
end
erase
clear
rbegin
rend
returns an iterator (-> first element)
returns an iterator (-> after last element)
erase 1 or more elements
erase all elements
returns reverse_iterator
returns reverse_iterator
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Element Types for Containers

Must have correct copy semantics
• bitwise default, or
• overload the assignment ( = ) operator and copy
constructor

Provide operator < and operator ==
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Types 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.
Copyright 2003, Kip R.Irvine
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Types of Iterators (cont)

Forward Iterator (FwdIt)
• reads and writes in forward direction only
• retains its position in the container
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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.
Copyright 2003, Kip R.Irvine
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Iterator Support, by Container
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stack, queue, priority_queue:
list, set, multiset, map, multimap:
vector, deque:
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no iterators
bidirectional
random
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Invalidating 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!
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Sequence Containers
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vector Container
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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
Copyright 2003, Kip R.Irvine
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Common vector Functions

push_back, pop_back
• add to end, remove from end

size
• current number of elements
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capacity
• storage allocation size
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begin, end
• return iterator and const_iterator
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rbegin, rend
• return reverse_iterator and const_reverse_iterator
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front, back
• return first and last elements
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Common vector Functions
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
at( )
operator [ ]
(also found in deque)
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list Sequence Container
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efficient insertion and deletion at any location
• deque is more efficient if insertions and deletions are at the
ends of the container
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implemented as doubly-linked list
• supports bidirectional iterators

does not support
• at( ) or operator [ ]
Copyright 2003, Kip R.Irvine
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list 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 list
void pop_front( )
• removes one element from the front of the list
void remove( const T& x )
• removes all elements found to be equal to X
Copyright 2003, Kip R.Irvine
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Unique list 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
Copyright 2003, Kip R.Irvine
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Creating a list
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
Copyright 2003, Kip R.Irvine
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Printing a list
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;
}
}
Copyright 2003, Kip R.Irvine
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Removing list Duplicates
list<int> scores;
scores.push_back(
scores.push_back(
scores.push_back(
scores.push_back(
scores.unique( );
print( scores );
10
20
30
30
);
);
);
);
// 10, 20, 30
Copyright 2003, Kip R.Irvine
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List 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 );
Copyright 2003, Kip R.Irvine
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Associative Containers
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Associative Containers

keys are always kept in sorted order
• iterator always traverses in sort order

set – single key values
• equivalent to Java's TreeSet
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multiset – duplicate keys allowed
map – contains pairs (key, value)
• key is unique
• equivalent to Java's TreeMap

multimap
• key need not be unique
Copyright 2003, Kip R.Irvine
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Sets: Three Ways to Insert Items
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insert single value, returning an iterator
iterator insert( const value_type & x);
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start searching for insert point after iterator it:
iterator insert( iterator it,
const value_type & x );
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insert sequence of elements in the range [first, last):
void insert( const value_type * first,
const value_type * last );
Copyright 2003, Kip R.Irvine
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Examples: 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 );
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Using typedef
Use typedef to simplify type definitions:
typedef multiset<int> msetInt;
.
msetInt A;
typedef multiset<int>::const_iterator msetIter;
.
msetIter = A.insert( 30 );
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Printing 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 << ", ";
}
}
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set Associative Container

keys are unique
• attempt to insert duplicate key is ignored

same functions as multiset
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map Associative Container
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unique keys and their associated values
each key is mapped to a single value
• values do not have to be unique
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fast storage and retrieval
sorted in order according to keys
Iterators point to pair<key,value>
• fields named first, second
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values can be inserted using [ ] operator
see: mapdemo.cpp
Copyright 2003, Kip R.Irvine
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Function Objects

template class that contains a function
• the function can be used in the same way as operator ( )
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make STL more flexible
• permit sorting on your own criteria
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predefined objects in STL:
•
•
•
•
•
•
divides< T >
equal_to< T >
greater< T >
greater_equal< T >
less< T >
etc.
Copyright 2003, Kip R.Irvine
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Function 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;
}
};
Copyright 2003, Kip R.Irvine
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Function Object Example
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
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;
Copyright 2003, Kip R.Irvine
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Binary 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;
}
};
Copyright 2003, Kip R.Irvine
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Binary Function Example
(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>() );
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Optional Information
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deque 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
Copyright 2003, Kip R.Irvine
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Common deque operations
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push_back( )
push_front( )
pop_back( )
pop_front( )
size( )
operator [ ]
at( )
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deque Example #1
Create a deque containing pointers to strings:
deque<Message *> mque;
mque.push_back(
mque.push_back(
mque.push_back(
mque.push_back(
new
new
new
new
Message(
Message(
Message(
Message(
"John", "How are you?" ));
"Sam", "What's happening?" ));
"Anne", "What's for dinner?" ));
"Bill", "Let's go surfing!" ));
Copyright 2003, Kip R.Irvine
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deque 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
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The End
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