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Introduction to map
Map is dictionary like data structure. It is a sequence of (key, value) pair, where only single value is associated with each unique key. It is often referred as associative array.
In map key values generally used to sort the elements. For map data type of key and value can differ and it is represented as
typedef pair<const Key, T> value_type;
Maps are typically implemented as Binary Search Tree.
Zero sized maps are also valid. In that case map.begin() and map.end() points to same location.
Definition
Below is definition of std::map from <map> header file
template < class Key,
class T,
class Compare = less<Key>,
class Alloc = allocator<pair<const Key,T> >
> class map;
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 <map>
Below is list of all methods from <map> header.
Constructors
| Sr.No. | Method & Description |
|---|---|
| 1 | map::map default constructor
Constructs an empty map with zero elements. |
| 2 | map::map range constructor
Constructs a map with as many elements as in range of first to last. |
| 3 | map::map copy constructor
Constructs a map with copy of each elements present in existing map. |
| 4 | map::map move constructor
Constructs a map with the contents of other using move semantics. |
| 5 | map::map initializer list constructor
Constructs a map from initialize list. |
Destructor
| Sr.No. | Method & Description |
|---|---|
| 1 | map::~map
Destroys map object by deallocating it”s memory. |
Member functions
| Sr.No. | Method & Description |
|---|---|
| 1 | map::at
Returns a reference to the mapped value associated with key k. |
| 2 | map::begin
Returns a iterator which refers to the first element of the map. |
| 3 | map::cbegin
Returns a constant iterator which refers to the first element of the map. |
| 4 | map::cend
Returns a constant iterator which points to past-the-end element of the map. |
| 5 | map::clear
Destroys the map by removing all elements and sets size of map to zero. |
| 6 | map::count
Returns number of mapped values associated with key k. |
| 7 | map::crbegin
Returns a constant reverse iterator which points to the last element of the container i. |
| 8 | map::crend
Returns a constant reverse iterator which points to the theoretical element preceding the first element in the container i. |
| 9 | map::emplace
Extends container by inserting new element. |
| 10 | map::emplace_hint hint version
Inserts a new element in a map using hint as a position for element. |
| 11 | map::empty
Tests whether map is empty or not. |
| 12 | map::end
Returns an iterator which points to past-the-end element in the map. |
| 13 | map::equal_range
Returns range of elements that matches specific key. |
| 14 | map::erase position version
Removes single element of the map from position. |
| 15 | map::erase position version
Removes single element of the map from position. |
| 16 | map::erase key
Removes mapped value associated with key k. |
| 17 | map::erase range version
Removes range of element from the the map. |
| 18 | map::erase range version
Removes range of element from the the map. |
| 19 | map::find
Finds an element associated with key k. |
| 20 | map::get_allocator
Returns an allocator associated with map. |
| 21 | map::insert single element
Extends container by inserting new element in map. |
| 22 | map::insert hint version
Extends container by inserting new element in map. |
| 23 | map::insert range version
Extends container by inserting new elements in the map. |
| 24 | map::insert move hint verstion
Extends map by inserting new element. |
| 25 | map::insert initializer list version
Extends map by inserting new element from initializer list. |
| 26 | map::key_comp
Returns a function object that compares the keys, which is a copy of this container”s constructor argument comp. |
| 27 | map::lower_bound
Returns an iterator pointing to the first element which is not less than key k. |
| 28 | map::max_size
Returns the maximum number of elements can be held by map. |
| 29 | map::operator= copy version
Assign new contents to the map by replacing old ones and modifies size if necessary. |
| 30 | map::operator= move version
Move the contents of one map into another and modifies size if necessary. |
| 31 | map::operator= initializer list version
Copy elements from initializer list to map. |
| 32 | map::operator[] copy version
If key k matches an element in the container, then method returns a reference to the element. |
| 33 | map::operator[] move version
If key k matches an element in the container, then method returns a reference to the element. |
| 34 | map::rbegin
Returns a reverse iterator which points to the last element of the map. |
| 35 | map::rend
Returns a reverse iterator which points to the reverse end of the map i. |
| 36 | map::size
Returns the number of elements present in the map. |
| 37 | map::swap
Exchanges the content of map with contents of map x. |
| 38 | map::upper_bound
Returns an iterator pointing to the first element which is greater than key k. |
| 39 | map::value_comp
Returns a function object that compares objects of type std::map::value_type. |
Non-member overloaded functions
| Sr.No. | Method & Description |
|---|---|
| 1 | operator==
Tests whether two maps are equal or not. |
| 2 | operator!=
Tests whether two maps are equal or not. |
| 3 | operator<
Tests whether first map is less than other or not. |
| 4 | map::operator<=
Tests whether first map is less than or equal to other or not. |
| 5 | operator>
Tests whether first map is greater than other or not. |
| 6 | operator>=
Tests whether first map is greater than or equal to other or not. |
| 7 | swap()
Exchanges the content of map with contents of map x. |
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 position version
Removes single element of the multimap from position. |
| 14 | multimap::erase position version
Removes single element of the multimap from position. |
| 15 | multimap::erase key
Removes mapped value associated with key k. |
| 16 | multimap::erase range version
Removes range of element from the the multimap. |
| 17 | multimap::erase range version
Removes range of element from the the multimap. |
| 18 | multimap::find
Finds an element associated with key k. |
| 19 | multimap::get_allocator
Returns an allocator associated with multimap. |
| 20 | multimap::insert single element
Extends container by inserting new element in multimap. |
| 21 | multimap::insert hint version
Extends container by inserting new element in multimap. |
| 22 | multimap::insert range version
Extends container by inserting new elements in the multimap. |
| 23 | multimap::insert move hint verstion
Extends multimap by inserting new element. |
| 24 | multimap::insert initializer list version
Extends multimap by inserting new element from initializer list. |
| 25 | multimap::key_comp
Returns a function object that compares the keys, which is a copy of this container”s constructor argument comp. |
| 26 | multimap::lower_bound
Returns an iterator pointing to the first element which is not less than key k. |
| 27 | multimap::max_size
Returns the maximum number of elements can be held by multimap. |
| 28 | multimap::operator= copy version
Assign new contents to the multimap by replacing old ones and modifies size if necessary. |
| 29 | multimap::operator= move version
Move the contents of one multimap into another and modifies size if necessary. |
| 30 | multimap::operator= initializer list version
Copy elements from initializer list to multimap. |
| 31 | multimap::rbegin
Returns a reverse iterator which points to the last element of the multimap. |
| 32 | multimap::rend
Returns a reverse iterator which points to the reverse end of the multimap. |
| 33 | multimap::size
Returns the number of elements present in the multimap. |
| 34 | multimap::swap
Exchanges the content of multimap with contents of multimap x. |
| 35 | multimap::upper_bound
Returns an iterator pointing to the first element which is greater than key k. |
| 36 | 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 | multimap::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. |
| 7 | swap()
Exchanges the content of multimap with contents of multimap x. |
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