Library: Containers
Does not inherit
An associative container that gives access to non-key values using keys. multimap keys are not required to be unique. A multimap supports bidirectional iterators.
#include <map>
namespace std {
template <class Key, class T, class Compare = less<Key>,
class Allocator = allocator<pair<const Key, T> > >
class multimap;
}
multimap gives fast access to stored values of type T that are indexed by keys of type Key. The default operation for key comparison is the < operator. Unlike map, multimap allows insertion of duplicate keys.
multimap uses 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 multimap 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 multimap {
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;
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 multimap<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 multimap(const Compare& = Compare(),
const Allocator& = Allocator());
template <class InputIterator>
multimap(InputIterator, InputIterator,
const Compare& = Compare(),
const Allocator& = Allocator());
multimap(const multimap<Key, T, Compare, Allocator>&);
multimap operator=
(const multimap<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;
// Modifiers
iterator 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(multimap<Key, T, Compare, Allocator>&);
void clear();
// Observers
key_compare key_comp() const;
value_compare value_comp() const;
// Multimap operations
iterator find(const key_type&);
const_iterator find(const key_type&) 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 Operators
template <class Key, class T, class Compare,
class Allocator>
bool operator== (const multimap<Key, T, Compare,
Allocator>&,
const multimap<Key, T, Compare,
Allocator>&);
template <class Key, class T, class Compare,
class Allocator>
bool operator!=(const multimap<Key, T, Compare,
Allocator>&,
const multimap<Key, T, Compare,
Allocator>&);
template <class Key, class T, class Compare,
class Allocator>
bool operator< (const multimap<Key, T, Compare,
Allocator>&,
const multimap<Key, T, Compare,
Allocator>&);
template <class Key, class T, class Compare,
class Allocator>
bool operator>(const multimap<Key, T, Compare,
Allocator>&,
const multimap<Key, T, Compare,
Allocator>&);
template <class Key, class T, class Compare,
class Allocator>
bool operator<=(const multimap<Key, T, Compare,
Allocator>&,
const multimap<Key, T, Compare,
Allocator>&);
template <class Key, class T, class Compare,
class Allocator>
bool operator>=(const multimap<Key, T, Compare,
Allocator>&,
const multimap<Key, T, Compare,
Allocator>&);
// Specialized Algorithms
template <class Key, class T, class Compare,
class Allocator>
void swap(multimap<Key, T, Compare, Allocator>&,
multimap<Key, T, Compare, Allocator>&;
}
explicit multimap(const Compare& comp = Compare(),
const Allocator& alloc = Allocator());
Constructs an empty multimap that uses the optional relation comp to order keys and the allocator alloc for all storage management.
template <class InputIterator>
multimap(InputIterator start,
InputIterator finish,
const Compare& comp = Compare()
const Allocator& alloc = Allocator());
Constructs a multimap containing values in the range [start, finish). Creation of the new multimap is only guaranteed to succeed if the iterators start and finish return values of type pair<class Key, class T>.
multimap(const multimap<Key, T, Compare, Allocator>& x);
Creates a new multimap by copying all pairs of key and value from x.
multimap<Key, T, Compare, Allocator>& operator=(const multimap<Key, T, Compare, Allocator>& x);
Replaces the contents of *this with a copy of the multimap x.
allocator_type get_allocator() const;
Returns a copy of the allocator used by self for storage management.
iterator begin();
Returns a bidirectional iterator pointing to the first element stored in the multimap. "First" is defined by the multimap's comparison operator, Compare.
const_iterator begin() const;
Returns a const_iterator pointing to the first element stored in the multimap. "First" is defined by the multimap's comparison operator, Compare.
iterator end();
Returns a bidirectional iterator pointing to the last element stored in the multimap (in other words, the off-the-end value).
const_iterator end() const;
Returns a const_iterator pointing to the last element stored in the multimap.
reverse_iterator rbegin();
Returns a reverse_iterator pointing to the first element stored in the multimap. "First" is defined by the multimap's comparison operator, Compare.
const_reverse_iterator rbegin() const;
Returns a const_reverse_iterator pointing to the first element stored in the multimap.
reverse_iterator rend();
Returns a reverse_iterator pointing to the last element stored in the multimap (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 multimap.
void clear();
Erases all elements from the self.
size_type count(const key_type& x) const;
Returns the number of elements in the multimap with the key value x.
bool empty() const;
Returns true if the multimap is empty, false otherwise.
pair<iterator,iterator> equal_range(const key_type& 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 start, iterator finish);
If the iterators start and finish point to the same multimap and finish is reachable from start, all elements in the range [start, finish) are deleted from the multimap.
void erase(iterator position);
Deletes the multimap element pointed to by the iterator position.
size_type erase(const key_type& x);
Deletes the elements with the key value x from the multimap, if any exist. Returns the number of deleted elements, or 0 otherwise.
iterator find(const key_type& x);
Searches the multimap 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.
iterator insert(const value_type& x); iterator insert(iterator position, const value_type& x);
x is inserted into the multimap. 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) are inserted into the multimap. 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 multimap.
iterator lower_bound(const key_type& x);
Returns an iterator to the first multimap element whose key is greater than or equal to x. If no such element exists, then end() is returned.
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 multimap.
size_type size() const;
Returns the number of elements in the multimap.
void swap(multimap<Key, T, Compare, Allocator>& x);
Swaps the contents of the multimap x with the current multimap, *this.
iterator upper_bound(const key_type& x);
Returns an iterator to the first element whose key is less than or equal to x. If no such element exists, then end() is returned.
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 value_types (key,value pairs) using the comparison operation, Compare, of the current multimap.
bool
operator==(const multimap<Key, T, Compare, Allocator>& x,
const multimap<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.
bool
operator!=(const multimap<Key, T, Compare, Allocator>& x,
const multimap<Key, T, Compare, Allocator>& y);
Returns !(x==y).
bool
operator<(const multimap<Key, T, Compare, Allocator>& x,
const multimap<Key, T, Compare, Allocator>& y);
Returns true if x is lexicographically less than y. Otherwise, it returns false.
bool
operator>(const multimap<Key, T, Compare, Allocator>& x,
const multimap<Key, T, Compare, Allocator>& y);
Returns y < x.
bool
operator<=(const multimap<Key, T, Compare, Allocator>& x,
const multimap<Key, T, Compare, Allocator>& y);
Returns !(y < x).
bool
operator>=(const multimap<Key, T, Compare, Allocator>& x,
const multimap<Key, T, Compare, Allocator>& y);
Returns !(x < y).
template<class Key, class T, class Compare, class Allocator>
void swap(multimap<Key, T, Compare, Allocator>& a,
multimap<Key, T, Compare, Allocator>& b);
Swaps the contents of a and b.
//
// multimap.cpp
//
#include <iostream>
#include <map>
#include <string>
typedef std::multimap<int, std::string, std::less<int>,
std::allocator<std::pair<const int,
std::string> > >
months_type;
// Print out a multimap.
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).second << " has " << (*it).first
<< " days\n";
return out;
}
int main ()
{
// Create a multimap 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 with the number of days
// as the not necessarily unique key.
months.insert (value_type (31, std::string ("January")));
months.insert (value_type (28, std::string ("February")));
months.insert (value_type (31, std::string ("March")));
months.insert (value_type (30, std::string ("April")));
months.insert (value_type (31, std::string ("May")));
months.insert (value_type (30, std::string ("June")));
months.insert (value_type (31, std::string ("July")));
months.insert (value_type (31, std::string ("August")));
months.insert (value_type (30, std::string ("September")));
months.insert (value_type (31, std::string ("October")));
months.insert (value_type (30, std::string ("November")));
months.insert (value_type (31, std::string ("December")));
// Print out the months.
std::cout << "All months of the year\n" << months
<< std::endl;
// Find all months with 30 days.
std::pair<months_type::iterator, months_type::iterator> p
= months.equal_range (30);
// Print out the 30 day months.
std::cout << "\nMonths with 30 days\n";
for ( ; p.first != p.second; ++p.first)
std::cout << (*p.first).second << '\n';
return 0;
}
Program Output:
All months of the year February has 28 days April has 30 days June has 30 days September has 30 days November has 30 days January has 31 days March has 31 days May has 31 days July has 31 days August has 31 days October has 31 days December has 31 days Months with 30 days April June September November
Member function templates are used in all containers included in the Standard Template Library. For example, the constructor for multimap takes two templatized iterators:
template <class InputIterator>
multimap (InputIterator, InputIterator,
const Compare& = Compare(),
const Allocator& = Allocator());
multimap 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 multimap in the following two ways:
multimap<int,int>::value_type intarray[10];
multimap<int,int> first_map(intarry, intarray + 10);
multimap<int,int> second_multimap(first_multimap.begin(),
first_multimap.end());
You cannot construct a multimap this way:
multimap<long,long> long_multimap(first_multimap.begin(),first_multimap.end());
since the long_multimap and first_multimap are not the same type.
If your compiler does not support default template parameters, you must always supply the Compare template argument and the Allocator template argument. For instance, you must write:
multimap<int, int, less<int>, allocator<int> >
instead of:
multimap<int, int>
allocator, Containers, Iterators, map
ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 23.3.1