C++ Library - <multimap>

Introduction to multimap

Multimap is dictionary like data structure. It is a sequence of (key, value) pair, where multiple values can be associate with equivalent keys. It is often referred as associative array.

In multimap key values generally used to sort the elements. For multimap data type of key and value can differ and it is represented as

typedef pair<const Key, T> value_type;

Multimaps are typically implemented as Binary Search Tree.

Zero sized multimaps are also valid. In that case multimap.begin() and multimap.end() points to same location.

Definition

Below is definition of std::multimap from <multimap> header file

template < class Key,
           class T,
           class Compare = less<Key>,
           class Alloc = allocator<pair<const Key,T> >
           > class multimap;

Parameters

Key − Type of the key.
T − Type of the mapped values.
Compare − A binary predicate that takes two element keys as arguments and returns a bool.
Alloc − Type of the allocator object.

T may be substituted by any other data type including user-defined type.

Member types

Following member types can be used as parameters or return type by member functions.

Sr.No.	Member types	Definition
1	key_type	Key (First parameter of the template)
2	mapped_type	T (Second parameter of the template)
3	key_compare	Compare (Third parameter of the template)
4	allocator_type	Alloc (Fourth parameter of the template)
5	value_type	pair<const key_type,mapped_type>
6	value_compare	Nested function class to compare elements
7	reference	allocator_type::reference
8	const_reference	allocator_type::const_reference
9	pointer	allocator_type::pointer
10	const_pointer	allocator_type::const_pointer
11	iterator	bi-directional iterator to `value_type`
12	const_iterator	bi-directional iterator to const `value_type`
13	reverse_iterator	reverse iterator
14	const_reverse_iterator	constant reverse iterator
15	difference_type	ptrdiff_t
16	size_type	size_t

Functions from <multimap>

Below is list of all methods from <multimap> header.

Constructors

Sr.No.	Method & Description
1	multimap::multimap `default constructor` Constructs an empty multimap with zero elements.
2	multimap::multimap `range constructor` Constructs a multimap with as many elements as in range of `first` to `last`.
3	multimap::multimap `copy constructor` Constructs a multimap with copy of each elements present in existing multimap.
4	multimap::multimap `move constructor` Constructs a multimap with the contents of other using move semantics.
5	multimap::multimap `initializer list constructor` Constructs a multimap from initialize list.

Destructor

Sr.No.	Method & Description
1	multimap::~multimap Destroys multimap object by deallocating it's memory.

Member functions

Sr.No.	Method & Description
1	multimap::begin Returns a iterator which refers to the first element of the multimap.
2	multimap::cbegin Returns a constant iterator which refers to the first element of the multimap.
3	multimap::cend Returns a constant iterator which points to `past-the-end` element of the multimap.
4	multimap::clear Destroys the multimap by removing all elements and sets size of multimap to zero.
5	multimap::count Returns number of multimapped values associated with key `k`.
6	multimap::crbegin Returns a constant reverse iterator which points to the last element of the container.
7	multimap::crend Returns a constant reverse iterator which points to the theoretical element preceding the first element in the container.
8	multimap::emplace Extends container by inserting new element.
9	multimap::emplace_hint `hint version` Inserts a new element in a multimap using hint as a position for element.
10	multimap::empty Tests whether multimap is empty or not.
11	multimap::end Returns an iterator which points to `past-the-end` element in the multimap.
12	multimap::equal_range Returns range of elements that matches specific key.
13	multimap::erase The erase() function is used to remove the elements from a container.
14	multimap::find Finds an element associated with key `k`.
15	multimap::get_allocator Returns an allocator associated with multimap.
16	multimap::insert The C++ insert() function is used to add elements to a multimap container.
17	multimap::key_comp Returns a function object that compares the keys, which is a copy of this container's constructor argument `comp`.
18	multimap::lower_bound Returns an iterator pointing to the first element which is not less than key `k`.
19	multimap::max_size Returns the maximum number of elements can be held by multimap.
20	multimap::operator= The operator=() function is used to assigns the contents of one multimap to another
21	multimap::rbegin Returns a reverse iterator which points to the last element of the multimap.
22	multimap::rend Returns a reverse iterator which points to the reverse end of the multimap.
23	multimap::size Returns the number of elements present in the multimap.
24	multimap::swap Exchanges the content of multimap with contents of multimap x.
25	multimap::upper_bound Returns an iterator pointing to the first element which is greater than key `k`.
26	multimap::value_comp Returns a function object that compares objects of type `std::multimap::value_type`.

Non-member overloaded functions

Sr.No.	Method & Description
1	operator== Tests whether two multimaps are equal or not.
2	operator!= Tests whether two multimaps are equal or not.
3	operator< Tests whether first multimap is less than other or not.
4	operator<= Tests whether first multimap is less than or equal to other or not.
5	operator> Tests whether first multimap is greater than other or not.
6	operator>= Tests whether first multimap is greater than or equal to other or not.

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