Library: Containers
Does not inherit
An associative container with access to non-key values using unique keys. A map supports bidirectional iterators.
#include <map>
namespace std {
template <class Key, class T, class Compare = less<Key>,
class Allocator = allocator<pair<const Key, T> > >
class map;
}
map 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.
namespace std {
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 Allocator::pointer pointer;
typedef typename Allocator::const_pointer const_pointer;
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
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;
};
// Nonmember 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>&);
}
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 start, InputIterator finish,
const Compare& comp = Compare(),
const Allocator& alloc = Allocator());
Constructs a map containing values in the range [start, finish). Creation of the new map is only guaranteed to succeed if the iterators start and finish return values of type pair<class Key, class Value> and all values of Key in the range[start, finish) 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.
allocator_type get_allocator() const;
Returns a copy of the allocator used by self for storage management.
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, to 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; in other words, to the off-the-end value).
const_reverse_iterator rend() const;
Returns a const_reverse_iterator pointing to the last element stored in the map.
map 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.
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 position.
void erase(iterator start, iterator finish);
If the iterators start and finish point to the same map and last is reachable from first, all elements in the range [start, finish) are deleted from the map.
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 is done right after position, then it takes amortized constant time. Otherwise it takes O(log N) time.
template <class InputIterator> void insert(InputIterator start, InputIterator finish);
Copies of each element in the range [start, finish) that possess a unique key (one not already in the map) are inserted into the map. The iterators start and finish 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 an iterator for the first entry with a key greater than 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.
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).
template <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.
//
// map.cpp
//
#include <iostream> // for cout
#include <map> // for map
#include <string> // for string
#include <utility> // for pair
typedef std::map<std::string, int, std::less<std::string>,
std::allocator<std::pair<const std::string,
int> > >
months_type;
// Print out a map.
inline std::ostream&
operator<< (std::ostream &out, const months_type &m)
{
for (months_type::const_iterator it = m.begin ();
it != m.end (); ++it)
std::cout << (*it).first << " has "
<< (*it).second << " days\n";
return out;
}
int main ()
{
// 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 (std::string ("January"), 31));
months.insert (value_type (std::string ("February"), 28));
months.insert (value_type (std::string ("February"), 29));
months.insert (value_type (std::string ("March"), 31));
months.insert (value_type (std::string ("April"), 30));
months.insert (value_type (std::string ("May"), 31));
months.insert (value_type (std::string ("June"), 30));
months.insert (value_type (std::string ("July"), 31));
months.insert (value_type (std::string ("August"), 31));
months.insert (value_type (std::string ("September"), 30));
months.insert (value_type (std::string ("October"), 31));
months.insert (value_type (std::string ("November"), 30));
months.insert (value_type (std::string ("December"), 31));
// Print out the months. Second February is not present.
std::cout << months << std::endl;
// Find the Number of days in June.
months_type::iterator p = months.find(std::string("June"));
// Print out the number of days in June.
if (p != months.end ())
std::cout << std::endl << (*p).first << " has "
<< (*p).second << " days\n";
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 June has 30 days
Member function templates are used in all containers included in the Standard Template Library. For example, the constructor for map 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 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, substitute functions 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());
You cannot construct a map 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.
If your compiler does not support template arguments, you must always supply the Compare template argument and the Allocator template argument. For instance, you must write:
map<int, int, less<int>, allocator<int> >
instead of:
map<int, int>
allocator, Containers, Iterators, multimap
ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 23.3.1