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map


Container

Summary

Data Type and Member Function Indexes

Synopsis

Description

Interface

Constructors and Destructors

Specialized Algorithms

Example

Warning

Summary

An associative container providing access to non-key values using unique keys. A map supports bidirectional iterators.

Data Type and Member Function Indexes
(exclusive of constructors and destructors)

Member Functions
begin() clear() count() empty() end() equal_range() erase() find() get_allocator() insert()	key_comp() lower_bound() max_size() operator!=() operator<() operator<=() operator=() operator==() ()">operator>() =()">operator>=()	operator[]() rbegin() rend() size() swap() upper_bound() value_comp()

Synopsis

#include <map>

template <class Key, class T, class Compare = less<Key> 
          class Allocator = allocator<T> >
class map;

Description

map <Key, T, Compare, Allocator> provides fast access to stored values of type T which are indexed by unique keys of type Key. The default operation for key comparison is the < operator.

map provides bidirectional iterators that point to an instance of pair<const Key x, T y> where x is the key and y is the stored value associated with that key. The definition of map provides a typedef to this pair called value_type.

The types used for both the template parameters Key and T must provide the following (where T is the type, t is a value of T and u is a const value of T):

  Copy constructors -  T(t) and T(u)
  Destructor        -  t.~T()
  Address of        -  &t and &u yielding T* and
                       const T* respectively
  Assignment        -  t = a where a is a
                       (possibly const) value of T

The type used for the Compare template parameter must satisfy the requirements for binary functions.

Interface

template <class Key, class T, class Compare = less<Key> 
          class Allocator = allocator<T> >
 class map {

public:

// types

   typedef Key key_type;
   typedef T mapped_type;
   typedef pair<const Key, T> value_type;
   typedef Compare key_compare;
   typedef Allocator allocator_type;
   typename reference;
   typename const_reference;
   typename iterator;
   typename const_iterator;
   typename size_type;
   typename difference_type;
   typename reverse_iterator;
   typename const_reverse_iterator;

   class value_compare
      : public binary_function<value_type, value_type, bool>
   {
     friend class map<Key, T, Compare, Allocator>;

     public :
       bool operator() (const value_type&,
                        const value_type&) const;
   };

// Construct/Copy/Destroy

   explicit map (const Compare& = Compare(),
                 const Allocator& = Allocator ());
   template <class InputIterator>
    map (InputIterator, InputIterator,
         const Compare& = Compare(),
         const Allocator& = Allocator ());
   map (const map<Key, T, Compare, Allocator>&);
   ~map();
   map<Key, T, Compare, Allocator>& 
    operator= (const map<Key, T, Compare, Allocator>&);
   allocator_type get_allocator () const;

// Iterators

   iterator begin();
   const_iterator begin() const;
   iterator end();
   const_iterator end() const;
   reverse_iterator rbegin();
   const_reverse_iterator rbegin() const;
   reverse_iterator rend();
   const_reverse_iterator rend() const;

// Capacity

   bool empty() const;
   size_type size() const;
   size_type max_size() const;

// Element Access

   mapped_type& operator[] (const key_type&);
   const mapped_type& operator[] (const key_type&) const;

// Modifiers

   pair<iterator, bool> insert (const value_type&);
   iterator insert (iterator, const value_type&);
   template <class InputIterator>
    void insert (InputIterator, InputIterator);

   iterator erase (iterator);
   size_type erase (const key_type&);
   iterator erase (iterator, iterator);
   void swap (map<Key, T, Compare, Allocator>&);

// Observers

   key_compare key_comp() const;
   value_compare value_comp() const;

// Map operations

   iterator find (const key_value&);
   const_iterator find (const key_value&) const;
   size_type count (const key_type&) const;
   iterator lower_bound (const key_type&);
   const_iterator lower_bound (const key_type&) const;
   iterator upper_bound (const key_type&);
   const_iterator upper_bound (const key_type&) const;
   pair<iterator, iterator> equal_range (const key_type&);
   pair<const_iterator, const_iterator>
     equal_range (const key_type&) const;
};

// Non-member Map Operators

template <class Key, class T, class Compare, class Allocator>
 bool operator== (const map<Key, T, Compare, Allocator>&,
                  const map<Key, T, Compare, Allocator>&);

template <class Key, class T, class Compare, class Allocator>
 bool operator!= (const map<Key, T, Compare, Allocator>&,
                  const map<Key, T, Compare, Allocator>&);

template <class Key, class T, class Compare, class Allocator>
 bool operator< (const map<Key, T, Compare, Allocator>&,
                 const map<Key, T, Compare, Allocator>&);

template <class Key, class T, class Compare, class Allocator>
 bool operator> (const map<Key, T, Compare, Allocator>&,
                 const map<Key, T, Compare, Allocator>&);

template <class Key, class T, class Compare, class Allocator>
 bool operator<= (const map<Key, T, Compare, Allocator>&,
                 const map<Key, T, Compare, Allocator>&);

template <class Key, class T, class Compare, class Allocator>
 bool operator>= (const map<Key, T, Compare, Allocator>&,
                 const map<Key, T, Compare, Allocator>&);


// Specialized Algorithms

template <class Key, class T, class Compare, class Allocator>
 void swap (map<*Key,T,Compare,Allocator>&,
            map<Key,T,Compare,Allocator>&);

Constructors and Destructors

explicit map(const Compare& comp = Compare(),
             const Allocator& alloc = Allocator());

Default constructor. Constructs an empty map that will use the relation comp to order keys, if it is supplied. The map will use the allocator alloc for all storage management.

template <class InputIterator>
map(InputIterator first, InputIterator last,
    const Compare& comp = Compare(),
    const Allocator& alloc = Allocator());

Constructs a map containing values in the range [first, last). Creation of the new map is only guaranteed to succeed if the iterators first and last return values of type pair<class Key, class Value> and all values of Key in the range[first, last) are unique. The map will use the relation comp to order keys, and the allocator alloc for all storage management.

map(const map<Key,T,Compare,Allocator>& x);

Copy constructor. Creates a new map by copying all pairs of key and value from x.

~map();

The destructor. Releases any allocated memory for this map.

Allocator

allocator_type get_allocator() const;

Returns a copy of the allocator used by self for storage management.

Iterators

iterator 
begin() ;

Returns an iterator pointing to the first element stored in the map. "First" is defined by the map's comparison operator, Compare.

const_iterator 
begin() const;

Returns a const_iterator pointing to the first element stored in the map.

iterator 
end() ;

Returns an iterator pointing to the last element stored in the map, i.e., the off-the-end value.

const_iterator 
end() const;

Returns a const_iterator pointing to the last element stored in the map.

reverse_iterator 
rbegin();

Returns a reverse_iterator pointing to the first element stored in the map. "First" is defined by the map's comparison operator, Compare.

const_reverse_iterator 
rbegin() const;

Returns a const_reverse_iterator pointing to the first element stored in the map.

reverse_iterator 
rend() ;

Returns a reverse_iterator pointing to the last element stored in the map, i.e., the off-the-end value.

const_reverse_iterator 
rend() const;

Returns a const_reverse_iterator pointing to the last element stored in the map.

Member Operators

map<Key, T, Compare, Allocator>& 
operator=(const map<Key, T, Compare, Allocator>& x);

Assignment. Replaces the contents of *this with a copy of the map x.

mapped_type& 
operator[](const key_type& x);

If an element with the key x exists in the map, then a reference to its associated value will be returned. Otherwise the pair x,T() will be inserted into the map and a reference to the default object T() will be returned.

Allocator

allocator_type 
get_allocator() const;

Returns a copy of the allocator used by self for storage management.

Member Functions

void
clear();

Erases all elements from the self.

size_type 
count(const key_type& x) const;

Returns a 1 if a value with the key x exists in the map, otherwise returns a 0.

bool 
empty() const;

Returns true if the map is empty, false otherwise.

pair<iterator, iterator> 
equal_range (const  key_type& x);

Returns the pair, (lower_bound(x), upper_bound(x)).

pair<const_iterator,const_iterator> 
equal_range (const key_type& x) const;

Returns the pair, (lower_bound(x), upper_bound(x)).

iterator
erase(iterator position);

Deletes the map element pointed to by the iterator position. Returns an iterator pointing to the element following the deleted element, or end() if the deleted item was the last one in this list.

iterator
erase(iterator first, iterator last);

Providing the iterators first and last point to the same map and last is reachable from first, all elements in the range (first, last) will be deleted from the map. Returns an iterator pointing to the element following the last deleted element, or end() if there were no elements after the deleted range.

size_type 
erase(const key_type& x);

Deletes the element with the key value x from the map, if one exists. Returns 1 if x existed in the map, 0 otherwise.

iterator 
find(const key_type& x);

Searches the map for a pair with the key value x and returns an iterator to that pair if it is found. If such a pair is not found the value end() is returned.

const_iterator 
find(const key_type& x) const;

Same as find above but returns a const_iterator.

pair<iterator, bool> 
insert(const value_type& x);
iterator 
insert(iterator position, const value_type& x);

If a value_type with the same key as x is not present in the map, then x is inserted into the map. Otherwise, the pair is not inserted. A position may be supplied as a hint regarding where to do the insertion. If the insertion may be done right after position then it takes amortized constant time. Otherwise it will take O(log N) time.

template <class InputIterator>
void  
insert(InputIterator first, InputIterator last);

Copies of each element in the range [first, last) which possess a unique key, one not already in the map, will be inserted into the map. The iterators first and last must return values of type pair<T1,T2>. This operation takes approximately O(N*log(size()+N)) time.

key_compare 
key_comp() const;

Returns a function object capable of comparing key values using the comparison operation, Compare, of the current map.

iterator 
lower_bound(const key_type& x);

Returns a reference to the first entry with a key greater than or equal to x.

const_iterator 
lower_bound(const key_type& x) const;

Same as lower_bound above but returns a const_iterator.

size_type 
max_size() const;

Returns the maximum possible size of the map. This size is only constrained by the number of unique keys which can be represented by the type Key.

size_type 
size() const;

Returns the number of elements in the map.

void 
swap(map<Key, T, Compare, Allocator>& x);

Swaps the contents of the map x with the current map, *this.

iterator 
upper_bound(const key_type& x);

Returns a reference to the first entry with a key less than or equal to x.

const_iterator 
upper_bound(const key_type& x) const;

Same as upper_bound above but returns a const_iterator.

value_compare  
value_comp() const;

Returns a function object capable of comparing pair<const Key, T> values using the comparison operation, Compare, of the current map. This function is identical to key_comp for sets.

Non-member Operators

template <class Key, class T, class Compare, class Allocator>
bool 
operator==(const map<Key, T, Compare, Allocator>& x,
                 const map<Key, T, Compare, Allocator>& y);

Returns true if all elements in x are element-wise equal to all elements in y, using (T::operator==). Otherwise it returns false.

template <class Key, class T, class Compare, class Allocator>
bool 
operator!=(const map<Key, T, Compare, Allocator>& x,
                 const map<Key, T, Compare, Allocator>& y);

Returns !(x==y).

template <class Key, class T, class Compare, class Allocator>
bool 
operator<(const map<Key, T, Compare, Allocator>& x,
                const map<Key, T, Compare, Allocator>& y);

Returns true if x is lexicographically less than y. Otherwise, it returns false.

()">

template <class Key, class T, class Compare, class Allocator>
bool 
operator>(const map<Key, T, Compare, Allocator>& x,
                const map<Key, T, Compare, Allocator>& y);

Returns y < x.

template <class Key, class T, class Compare, class Allocator>
bool 
operator<=(const map<Key, T, Compare, Allocator>& x,
                const map<Key, T, Compare, Allocator>& y);

Returns !(y < x).

=()">

template <class Key, class T, class Compare, class Allocator>
bool 
operator>=(const map<Key, T, Compare, Allocator>& x,
                const map<Key, T, Compare, Allocator>& y);

Returns !(x < y).

Specialized Algorithms

template <class Key, class T, class Compare, class Allocator>
void 
swap(map<Key, T, Compare, Allocator>& a,
           map<Key, T, Compare, Allocator>& b);

Efficiently swaps the contents of a and b.

Example

//
// map.cpp
//
 #include <string>
 #include <map>
 #include <iostream.h>

 typedef map<string, int, less<string> > months_type;

 // Print out a pair
 template <class First, class Second>
 ostream& operator<<(ostream& out, 
                     const pair<First,Second> & p)
 {
   cout << p.first << " has " << p.second << " days";
   return out;
 }

 // Print out a map
 ostream& operator<<(ostream& out, const months_type & l)
 {
   copy(l.begin(),l.end(), ostream_iterator
                <months_type::value_type,char>(cout,"\n"));
   return out;
 }


 int main(void)
 {
   // create a map of months and the number of days 
   // in the month
   months_type months;

   typedef months_type::value_type value_type;
  
   // Put the months in the multimap
   months.insert(value_type(string("January"),   31));
   months.insert(value_type(string("February"),   28));
   months.insert(value_type(string("February"),   29));
   months.insert(value_type(string("March"),     31));
   months.insert(value_type(string("April"),     30));
   months.insert(value_type(string("May"),       31));
   months.insert(value_type(string("June"),      30));
   months.insert(value_type(string("July"),      31));
   months.insert(value_type(string("August"),    31));
   months.insert(value_type(string("September"), 30));
   months.insert(value_type(string("October"),   31));
   months.insert(value_type(string("November"),  30));
   months.insert(value_type(string("December"),  31));

   // print out the months
   // Second February is not present
   cout << months << endl;

   // Find the Number of days in June
   months_type::iterator p = months.find(string("June"));

   // print out the number of days in June
   if (p != months.end())
     cout << endl << *p << endl;
  
   return 0;
 }

Output :
April has 30 days
August has 31 days
December has 31 days
February has 28 days
January has 31 days
July has 31 days
June has 30 days
March has 31 days
May has 31 days
November has 30 days
October has 31 days
September has 30 days

Warning

Member function templates are used in all containers provided by the Standard Template Library. An example of this feature is the constructor for map<Key,T,Compare,Allocator> that takes two templated iterators:

template <class InputIterator>
 map (InputIterator, InputIterator, const Compare& = Compare(),
      const Allocator& = Allocator());

map also has an insert function of this type. These functions, when not restricted by compiler limitations, allow you to use any type of input iterator as arguments. For compilers that do not support this feature, we provide substitute functions that allow you to use an iterator obtained from the same type of container as the one you are constructing (or calling a member function on), or you can use a pointer to the type of element you have in the container.

For example, if your compiler does not support member function templates, you can construct a map in the following two ways:

map<int, int, less<int> >::value_type intarray[10];
map<int, int, less<int> > first_map(intarray, intarray + 10);
map<int, int, less<int> > second_map(first_map.begin(),
                                     first_map.end());

But not this way:

map<long, long, less<long> > long_map(first_map.begin(),
                                      first_map.end());

Since the long_map and first_map are not the same type.

Also, many compilers do not support default template arguments. If your compiler is one of these, you need to always supply the Compare template argument and the Allocator template argument. For instance, you'll have to write:

map<int, int, less<int>,  allocator<int> >

instead of:

map<int, int>

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map

map

Summary

Data Type and Member Function Indexes
(exclusive of constructors and destructors)

Synopsis

Description

Interface

Constructors and Destructors

Allocator

Iterators

Member Operators

Allocator

Member Functions

Non-member Operators

Specialized Algorithms

Example

Warning

See Also

ICTP Portal

Sections

Personal tools

Document Actions

map

map

Summary

Data Type and Member Function Indexes(exclusive of constructors and destructors)

Synopsis

Description

Interface

Constructors and Destructors

Allocator

Iterators

Member Operators

Allocator

Member Functions

Non-member Operators

Specialized Algorithms

Example

Warning

See Also

Data Type and Member Function Indexes
(exclusive of constructors and destructors)