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Category: containers | | Component type: type |
Description
Multimap
is a SortedAssociativeContainer that associates objects of type Key
with objects of type Data
. multimap
is a PairAssociativeContainer, meaning that its value type is pair<const Key, Data>
. It is also a MultipleAssociativeContainer, meaning that there is no limit on the number of elements with the same key.
Multimap
has the important property that inserting a new element into a multimap
does not invalidate iterators that point to existing elements. Erasing an element from a multimap
also does not invalidate any iterators, except, of course, for iterators that actually point to the element that is being erased.
Example
struct ltstr
{
bool operator()(const char* s1, const char* s2) const
{
}
};
int main()
{
multimap<const char*, int, ltstr> m;
m.insert(pair<const char* const, int>("a", 1));
m.insert(pair<const char* const, int>("c", 2));
m.insert(pair<const char* const, int>("b", 3));
m.insert(pair<const char* const, int>("b", 4));
m.insert(pair<const char* const, int>("a", 5));
m.insert(pair<const char* const, int>("b", 6));
cout << "Number of elements with key a: " << m.count("a") << endl;
cout << "Number of elements with key b: " << m.count("b") << endl;
cout << "Number of elements with key c: " << m.count("c") << endl;
cout << "Elements in m: " << endl;
for (multimap<const char*, int, ltstr>::iterator it = m.begin();
it != m.end();
++it)
cout << " [" << (*it).first << ", " << (*it).second << "]" << endl;
}
Definition
Defined in the standard header map, and in the nonstandard backward-compatibility header multimap.h.
Template parameters
Parameter | Description | Default |
Key | The multimap's key type. This is also defined as multimap::key_type . | |
Data | The multimap's data type. This is also defined as multimap::data_type . | |
Compare | The key comparison function, a StrictWeakOrdering whose argument type is key_type ; it returns true if its first argument is less than its second argument, and false otherwise. This is also defined as multimap::key_compare . | less<Key> |
Alloc | The multimap 's allocator, used for all internal memory management. | Allocators |
Model of
MultipleSortedAssociativeContainer, PairAssociativeContainer
Type requirements
Public base classes
None.
Members
Member | Where defined | Description |
key_type | AssociativeContainer | The multimap 's key type, Key . |
data_type | PairAssociativeContainer | The type of object associated with the keys. |
value_type | PairAssociativeContainer | The type of object, pair<const key_type, data_type> , stored in the multimap. |
key_compare | SortedAssociativeContainer | functors that compares two keys for ordering. |
value_compare | SortedAssociativeContainer | functors that compares two values for ordering. |
pointer | Container | Pointer to T . |
reference | Container | Reference to T |
const_reference | Container | Const reference to T |
size_type | Container | An unsigned integral type. |
difference_type | Container | A signed integral type. |
iterator | Container | Iterator used to iterate through a multimap . [1] |
const_iterator | Container | Const iterator used to iterate through a multimap . |
reverse_iterator | ReversibleContainer | Iterator used to iterate backwards through a multimap . [1] |
const_reverse_iterator | ReversibleContainer | Const iterator used to iterate backwards through a multimap . |
iterator begin() | Container | Returns an iterator pointing to the beginning of the multimap . |
iterator end() | Container | Returns an iterator pointing to the end of the multimap . |
const_iterator begin() const | Container | Returns a const_iterator pointing to the beginning of the multimap . |
const_iterator end() const | Container | Returns a const_iterator pointing to the end of the multimap . |
reverse_iterator rbegin() | ReversibleContainer | Returns a reverse_iterator pointing to the beginning of the reversed multimap. |
reverse_iterator rend() | ReversibleContainer | Returns a reverse_iterator pointing to the end of the reversed multimap. |
const_reverse_iterator rbegin() const | ReversibleContainer | Returns a const_reverse_iterator pointing to the beginning of the reversed multimap. |
const_reverse_iterator rend() const | ReversibleContainer | Returns a const_reverse_iterator pointing to the end of the reversed multimap. |
size_type size() const | Container | Returns the size of the multimap . |
size_type max_size() const | Container | Returns the largest possible size of the multimap . |
bool empty() const | Container | true if the multimap 's size is 0 . |
key_compare key_comp() const | SortedAssociativeContainer | Returns the key_compare object used by the multimap . |
value_compare value_comp() const | SortedAssociativeContainer | Returns the value_compare object used by the multimap . |
multimap() | Container | Creates an empty multimap . |
multimap(const key_compare& comp) | SortedAssociativeContainer | Creates an empty multimap , using comp as the key_compare object. |
template <class InputIterator>
multimap(InputIterator f, InputIterator l)
[2] | MultipleSortedAssociativeContainer | Creates a multimap with a copy of a range. |
template <class InputIterator>
multimap(InputIterator f, InputIterator l,
const key_compare& comp)
[2] | MultipleSortedAssociativeContainer | Creates a multimap with a copy of a range, using comp as the key_compare object. |
multimap(const multimap&) | Container | The copy constructor. |
multimap& operator=(const multimap&) | Container | The assignment operator |
void swap(multimap&) | Container | Swaps the contents of two multimaps. |
iterator insert(const value_type& x) | MultipleAssociativeContainer | Inserts x into the multimap . |
iterator insert(iterator pos,
const value_type& x)
| MultipleSortedAssociativeContainer | Inserts x into the multimap , using pos as a hint to where it will be inserted. |
template <class InputIterator>
void insert(InputIterator, InputIterator)
[2] | MultipleSortedAssociativeContainer | Inserts a range into the multimap . |
void erase(iterator pos) | AssociativeContainer | Erases the element pointed to by pos . |
size_type erase(const key_type& k) | AssociativeContainer | Erases the element whose key is k . |
void erase(iterator first, iterator last) | AssociativeContainer | Erases all elements in a range. |
void clear() | AssociativeContainer | Erases all of the elements. |
iterator find(const key_type& k) | AssociativeContainer | Finds an element whose key is k . |
const_iterator find(const key_type& k) const | AssociativeContainer | Finds an element whose key is k . |
size_type count(const key_type& k) | AssociativeContainer | Counts the number of elements whose key is k . |
iterator lower_bound(const key_type& k) | SortedAssociativeContainer | Finds the first element whose key is not less than k . |
const_iterator lower_bound(const key_type& k) const | SortedAssociativeContainer | Finds the first element whose key is not less than k . |
iterator upper_bound(const key_type& k) | SortedAssociativeContainer | Finds the first element whose key greater than k . |
const_iterator upper_bound(const key_type& k) const | SortedAssociativeContainer | Finds the first element whose key greater than k . |
| SortedAssociativeContainer | Finds a range containing all elements whose key is k . |
pair<const_iterator, const_iterator>
| SortedAssociativeContainer | Finds a range containing all elements whose key is k . |
| ForwardContainer | Tests two multimaps for equality. This is a global function, not a member function. |
| ForwardContainer | Lexicographical comparison. This is a global function, not a member function. |
New members
All of multimap
's members are defined in the MultipleSortedAssociativeContainer and PairAssociativeContainer requirements. Multimap
does not introduce any new members.
Notes
[1] Multimap::iterator
is not a mutable iterator, because multimap::value_type
is not Assignable. That is, if i
is of type multimap::iterator
and p
is of type multimap::value_type
, then *i = p
is not a valid expression. However, multimap::iterator
isn't a constant iterator either, because it can be used to modify the object that it points to. Using the same notation as above, (*i).second = p
is a valid expression. The same point applies to multimap::reverse_iterator
.
[2] This member function relies on member template functions, which at present (early 1998) are not supported by all compilers. If your compiler supports member templates, you can call this function with any type of InputIterator. If your compiler does not yet support member templates, though, then the arguments must either be of type const value_type*
or of type multimap::const_iterator
.
See also
AssociativeContainer, SortedAssociativeContainer, PairAssociativeContainer, MultipleSortedAssociativeContainer, set
, Map
multiset
, hash_set
, hash_map
, hash_multiset
, hash_multimap