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Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.
NAME
multimap
- 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.
SYNOPSIS
#include <map>
template <class Key, class T, class Compare = less<Key>,
class Allocator = allocator<pair<const Key, T>> >
class multimap;
DESCRIPTION
multimap_<Key_,T,_Compare,_Allocator> 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 defini-
tion 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.
INTERFACE
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 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 ();
multimap<Key, T, Compare, Allocator>& 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;
};
// Non-member 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>&;
CONSTRUCTORS
explicit multimap(const Compare& comp = Compare(),
const Allocator& alloc = Allocator());
Constructs an empty multimap that uses the optional rela-
tion comp to order keys and the allocator alloc for all
storage management.
template <class InputIterator>
multimap(InputIterator first,
InputIterator last,
const Compare& comp = Compare()
const Allocator& alloc = Allocator());
Constructs a multimap containing values in the range
[first, last). Creation of the new multimap is only
guaranteed to succeed if the iterators first and last
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.
DESTRUCTORS
~multimap();
Releases any allocated memory for this multimap.
ASSIGNMENT OPERATORS
multimap<Key, T, Compare, Allocator>&
operator=(const multimap<Key, T, Compare, Allocator>& x);
Replaces the contents of *this with a copy of the mul-
timap x.
ALLOCATORS
allocator_type
get_allocator() const;
Returns a copy of the allocator used by self for storage
management.
ITERATORS
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.
MEMBER FUNCTIONS
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 first, iterator last);
If the iterators first and last point to the same mul-
timap and last is reachable from first, all elements in
the range (first, last) are deleted from the multimap.
Returns an iterator pointing to the element following the
last deleted element or end(), if there were no elements
after the deleted range.
void
erase(iterator position);
Deletes the multimap 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.
size_type
erase(const key_type& x);
Deletes the elements with the key value x from the map,
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 sup-
plied 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 first, InputIterator last);
Copies of each element in the range [first, last) are
inserted into the multimap. 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
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 opera-
tion, Compare, of the current multimap.
NON-MEMBER OPERATORS
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. Oth-
erwise, 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).
SPECIALIZED ALGORITHMS
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.
EXAMPLE
//
// multimap.cpp
//
#include <string>
#include <map>
#include <iostream>
using namespace std;
typedef multimap<int, string, less<int> > months_type;
// Print out a pair
template <class First, class Second>
ostream& operator<<(ostream& out,
const pair<First,Second>& p)
{
cout << p.second << " has " << p.first << " days";
return out;
}
// Print out a multimap
ostream& operator<<(ostream& out, months_type l)
{
copy(l.begin(),l.end(), ostream_iterator
<months_type::value_type,char>(cout,"\n"));
return out;
}
int main(void)
{
// 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
months.insert(value_type(31, string("January")));
months.insert(value_type(28, string("February")));
months.insert(value_type(31, string("March")));
months.insert(value_type(30, string("April")));
months.insert(value_type(31, string("May")));
months.insert(value_type(30, string("June")));
months.insert(value_type(31, string("July")));
months.insert(value_type(31, string("August")));
months.insert(value_type(30, string("September")));
months.insert(value_type(31, string("October")));
months.insert(value_type(30, string("November")));
months.insert(value_type(31, string("December")));
// print out the months
cout << "All months of the year" << endl << months
<< endl;
// Find the Months with 30 days
pair<months_type::iterator,months_type::iterator> p =
months.equal_range(30);
// print out the 30 day months
cout << endl << "Months with 30 days" << endl;
copy(p.first,p.second,
ostream_iterator<months_type::value_type,char>
(cout,"\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 has 30 days
June has 30 days
September has 30 days
November 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
multimap<Key,T,Compare,Allocator> that 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 func-
tion templates, you can construct a multimap in the follow-
ing 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());
but not 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.
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:
multimap<int, int, less<int>, allocator<int> >
instead of:
multimap<int, int>
If your compiler does not support namespaces, then you do
not need the using declaration for std.
SEE ALSO
allocator, Containers, Iterators, map
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