map(3C++) - map(3C++)
Standard C++ Library Copyright 1998, Rogue Wave Software, Inc.
NAMEmap
- 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 opera‐
tion 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 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>&);
CONSTRUCTORSexplicit 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_iteratorbegin() const;
Returns a const_iterator pointing to the first element stored in the map.
iteratorend();
Returns an iterator pointing to the last element stored in the map (in
other words, the off-the-end value).
const_iteratorend() const;
Returns a const_iterator pointing to the last element stored in the map.
reverse_iteratorrbegin();
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_iteratorrbegin() const;
Returns a const_reverse_iterator pointing to the first element stored in
the map.
reverse_iteratorrend();
Returns a reverse_iterator pointing to the last element stored in the map
(in other words, the off-the-end value).
const_reverse_iteratorrend() 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_typecount(const key_type& x) const;
Returns a 1 if a value with the key x exists in the map. Otherwise returns
a 0.
boolempty() 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)).
voiderase(iterator position);
Deletes the map element pointed to by the iterator position.
voiderase(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 iterator pointing to the element following the last deleted
element, or end() if there were no elements after the deleted range.
size_typeerase(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.
iteratorfind(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);
iteratorinsert(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
is done right after position, then it takes amortized constant time. Other‐
wise it takes O(log N) time.
template <class InputIterator>
voidinsert(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_comparekey_comp() const;
Returns a function object capable of comparing key values using the compar‐
ison operation, Compare, of the current map.
iteratorlower_bound(const key_type& x);
Returns a reference to the first entry with a key greater than or equal to
x.
const_iteratorlower_bound(const key_type& x) const;
Same as lower_bound above but returns a const_iterator.
size_typemax_size() const;
Returns the maximum possible size of the map. This size is only con‐
strained by the number of unique keys that can be represented by the type
Key.
size_typesize() const;
Returns the number of elements in the map.
voidswap(map<Key, T, Compare, Allocator>& x);
Swaps the contents of the map x with the current map, *this.
iteratorupper_bound(const key_type& x);
Returns a reference to the first entry with a key less than or equal to x.
const_iteratorupper_bound(const key_type& x) const;
Same as upper_bound above but returns a const_iterator.
value_comparevalue_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 ALGORITHMStemplate <class Key, class T, class Compare, class Allocator>
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 mapostream& 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 OutputApril has 30 daysAugust has 31 daysDecember has 31 daysFebruary has 28 daysJanuary has 31 daysJuly has 31 daysJune has 30 daysMarch has 31 daysMay has 31 daysNovember has 30 daysOctober has 31 daysSeptember has 30 daysWARNINGS
Member function templates are used in all containers included in the
Standard Template Library. An example of this feature is the construc‐
tor for map<Key,T,Compare,Allocator> that takes two templatized itera‐
tors:
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 itera‐
tor as arguments. For compilers that do not support this feature, substitute
functions allow you to use an iterator obtained from the same type of con‐
tainer 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 com‐
piler is one of these, you always need to supply the Compare template argument
and the Allocator template 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
Rogue Wave Software 02 Apr 1998 map(3C++)