NAME

std::map - std::map

Synopsis


Defined in header <map>
template<
class Key,
class T, (1)
class Compare = std::less<Key>,
class Allocator = std::allocator<std::pair<const Key, T> >
> class map;
namespace pmr {
template <class Key, class T, class Compare = std::less<Key>>
using map = std::map<Key, T, Compare, (2) (since C++17)
std::pmr::polymorphic_allocator<std::pair<const Key,T>>>
}


std::map is a sorted associative container that contains key-value pairs with unique keys. Keys are sorted by using the comparison function Compare. Search, removal, and insertion operations have logarithmic complexity. Maps are usually implemented as red-black_trees.
Everywhere the standard library uses the Compare requirements, uniqueness is determined by using the equivalence relation. In imprecise terms, two objects a and b are considered equivalent (not unique) if neither compares less than the other: !comp(a, b) && !comp(b, a).
std::map meets the requirements of Container, AllocatorAwareContainer, AssociativeContainer and ReversibleContainer.

Member types


Member type Definition
key_type Key
mapped_type T
value_type std::pair<const Key, T>
size_type Unsigned integer type (usually std::size_t)
difference_type Signed integer type (usually std::ptrdiff_t)
key_compare Compare
allocator_type Allocator


reference Allocator::reference (until C++11)
                                value_type& (since C++11)


const_reference Allocator::const_reference (until C++11)
                                const value_type& (since C++11)


pointer Allocator::pointer (until C++11)
                                std::allocator_traits<Allocator>::pointer (since C++11)


const_pointer Allocator::const_pointer (until C++11)
                                std::allocator_traits<Allocator>::const_pointer (since C++11)


iterator LegacyBidirectionalIterator
const_iterator Constant LegacyBidirectionalIterator
reverse_iterator std::reverse_iterator<iterator>
const_reverse_iterator std::reverse_iterator<const_iterator>
node_type(since C++17) a specialization of node_handle representing a container node
                                type describing the result of inserting a node_type, a specialization of


                                  template <class Iter, class NodeType> struct /*unspecified*/ {
                                      Iter position;
insert_return_type(since C++17) bool inserted;
                                      NodeType node;
                                  };


                                instantiated with template arguments iterator and node_type.

Member classes


              compares objects of type value_type
value_compare (class)

Member functions


                 constructs the map
constructor (public member function)
                 destructs the map
destructor (public member function)
                 assigns values to the container
operator= (public member function)
                 returns the associated allocator
get_allocator (public member function)

Element access


at access specified element with bounds checking
                 (public member function)
(C++11)
                 access or insert specified element
operator[] (public member function)

Iterators


begin returns an iterator to the beginning
cbegin (public member function)


end_ returns an iterator to the end
cend (public member function)


rbegin returns a reverse iterator to the beginning
crbegin (public member function)


rend returns a reverse iterator to the end
crend (public member function)

Capacity


                 checks whether the container is empty
empty (public member function)
                 returns the number of elements
size (public member function)
                 returns the maximum possible number of elements
max_size (public member function)

Modifiers


                 clears the contents
clear (public member function)
                 inserts elements
                 or nodes
insert (since C++17)
                 (public member function)


insert_or_assign inserts an element or assigns to the current element if the key already exists
                 (public member function)
(C++17)


emplace constructs element in-place
                 (public member function)
(C++11)


emplace_hint constructs elements in-place using a hint
                 (public member function)
(C++11)


try_emplace inserts in-place if the key does not exist, does nothing if the key exists
                 (public member function)
(C++17)
                 erases elements
erase (public member function)
                 swaps the contents
swap (public member function)


extract extracts nodes from the container
                 (public member function)
(C++17)


merge splices nodes from another container
                 (public member function)
(C++17)

Lookup


                 returns the number of elements matching specific key
count (public member function)
                 finds element with specific key
find (public member function)


contains checks if the container contains element with specific key
                 (public member function)
(C++20)
                 returns range of elements matching a specific key
equal_range (public member function)
                 returns an iterator to the first element not less than the given key
lower_bound (public member function)
                 returns an iterator to the first element greater than the given key
upper_bound (public member function)

Observers


                 returns the function that compares keys
key_comp (public member function)
                 returns the function that compares keys in objects of type value_type
value_comp (public member function)

Non-member functions


operator==
operator!= lexicographically compares the values in the map
operator< (function template)
operator<=
operator>
operator>=
                    specializes the std::swap algorithm
std::swap(std::map) (function template)


erase_if(std::map) Erases all elements satisfying specific criteria
                    (function template)
(C++20)


Deduction_guides(since C++17)