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Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.
NAME
map
- An associative container with access to non-key values
using unique keys. A map supports bidirectional iterators.
SYNOPSIS
#include <map>
template <class Key, class T, class Compare = less<Key>
class Allocator = allocator<pair<const Key, T>> >
class map;
DESCRIPTION
map_<Key,_T,_Compare,_Allocator> gives fast access to stored
values of type T that are indexed by unique keys of type
Key. The default operation for key comparison is the <
operator.
map has 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
includes a typedef to this pair called value_type.
The types used for both the template parameters Key and T
must include 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<pair<const Key, T>> >
class map {
public:
// types
typedef Key key_type;
typedef typename Allocator::pointer pointer;
typedef typename Allocator::const_pointer const_pointer;
typedef T mapped_type;
typedef pair<const Key, T> value_type;
typedef Compare key_compare;
typedef Allocator allocator_type;
typedef typename
Allocator::reference reference;
typedef typename
Allocator::const_reference const_reference;
class iterator;
class const_iterator;
typedef typename
Allocator::size_type size_type;
typedef typename
Allocator::difference_type difference_type;
typedef typename std::reverse_iterator<iterator>
reverse_iterator;
typedef typename std::reverse_iterator<const_iterator>
const_reverse_iterator;
class value_compare
: public binary_function<value_type, value_type, bool>
{
friend class map<Key, T, Compare, Allocator>;
protected :
Compare comp;
value_compare(Compare c): comp(c) {}
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&);
// Modifiers
pair<iterator, bool> insert (const value_type&);
iterator insert (iterator, const value_type&);
template <class InputIterator>
void insert (InputIterator, InputIterator);
void erase (iterator);
size_type erase (const key_type&);
void erase (iterator, iterator);
void swap (map<Key, T, Compare, Allocator>&);
void clear();
// 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 Alloca-
tor>
bool operator== (const map<Key, T, Compare, Allocator>&,
const map<Key, T, Compare, Allocator>&);
template <class Key, class T, class Compare, class Alloca-
tor>
bool operator!= (const map<Key, T, Compare, Allocator>&,
const map<Key, T, Compare, Allocator>&);
template <class Key, class T, class Compare, class Alloca-
tor>
bool operator< (const map<Key, T, Compare, Allocator>&,
const map<Key, T, Compare, Allocator>&);
template <class Key, class T, class Compare, class Alloca-
tor>
bool operator> (const map<Key, T, Compare, Allocator>&,
const map<Key, T, Compare, Allocator>&);
template <class Key, class T, class Compare, class Alloca-
tor>
bool operator<= (const map<Key, T, Compare, Allocator>&,
const map<Key, T, Compare, Allocator>&);
template <class Key, class T, class Compare, class Alloca-
tor>
bool operator>= (const map<Key, T, Compare, Allocator>&,
const map<Key, T, Compare, Allocator>&);
// Specialized Algorithms
template <class Key, class T, class Compare, class Alloca-
tor>
void swap (map<*Key,T,Compare,Allocator>&,
map<Key,T,Compare,Allocator>&);
CONSTRUCTORS
explicit map(const Compare& comp = Compare(),
const Allocator& alloc = Allocator());
Constructs an empty map that uses the relation comp to
order keys, if it is supplied. The map uses 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 uses
the relation comp to order keys, and the allocator alloc
for all storage management.
map(const map<Key,T,Compare,Allocator>& x);
Creates a new map by copying all pairs of key and value
from x.
DESTRUCTORS
~map();
Releases any allocated memory for this map.
ALLOCATORS
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 (in other words, 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 com-
parison 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 (in other words, 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);
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 is returned. Otherwise
the pair x,T() is inserted into the map and a reference
to the default object T() is returned.
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)).
void
erase(iterator position);
Deletes the map element pointed to by the iterator posi-
tion. Returns an iterator pointing to the element follow-
ing the deleted element, or end() if the deleted item was
the last one in this list.
void
erase(iterator first, iterator last);
If the iterators first and last point to the same map and
last is reachable from first, all elements in the range
(first, last) are deleted from the map. Returns an itera-
tor 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 other-
wise.
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 inser-
tion is done right after position, then it takes amor-
tized constant time. Otherwise it takes O(log N) time.
template <class InputIterator>
void
insert(InputIterator first, InputIterator last);
Copies of each element in the range [first, last) that
possess a unique key (one not already in the map) are
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 that 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 Alloca-
tor>
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 Alloca-
tor>
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 Alloca-
tor>
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. Oth-
erwise, it returns false.
template <class Key, class T, class Compare, class Alloca-
tor>
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 Alloca-
tor>
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 Alloca-
tor>
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 Alloca-
tor>
void swap(map<Key, T, Compare, Allocator>& a,
map<Key, T, Compare, Allocator>& b);
Swaps the contents of a and b.
EXAMPLE
//
// map.cpp
//
#include <string>
#include <map>
#include <iostream>
using namespace std;
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;
}
Program 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
WARNINGS
Member function templates are used in all containers
included in the Standard Template Library. An example of
this feature is the constructor for
map<Key,T,Compare,Allocator> that takes two templatized
iterators:
template <class InputIterator>
map (InputIterator, InputIterator,
const Compare& = Compare(),
const Allocator& = Allocator());
map also has an insert function of this type. These func-
tions, when not restricted by compiler limitations, allow
you to use any type of input iterator as arguments. For com-
pilers that do not support this feature, substitute func-
tions allow you to use an iterator obtained from the same
type of container as the one you are constructing (or cal-
ling 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 func-
tion 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 argu-
ments. If your compiler is one of these, you always need to
supply the Compare template argument and the Allocator tem-
plate argument. For instance, you have to write:
map<int, int, less<int>, allocator<int> >
instead of:
map<int, int>
If your compiler does not support namespaces, then you do
not need the using declaration for std.
SEE ALSO
allocator, Containers, Iterators, multimap
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