std::map - std::map


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*/ { insert_return_type(since Iter position; C++17) bool inserted;
                             NodeType node;

                         instantiated with template arguments iterator and node_type.

Member classes

value_compare compares objects of type value_type

Member functions

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

Element access

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


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)


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


clear clears the contents
                 (public member function)
                 inserts elements insert or nodes
                 (since C++17)
                 (public member function) insert_or_assign inserts an element or assigns to the current element if the key (C++17) already exists
                 (public member function) emplace constructs element in-place (C++11) (public member function) emplace_hint constructs elements in-place using a hint (C++11) (public member function) try_emplace inserts in-place if the key does not exist, does nothing if the key (C++17) exists
                 (public member function) erase erases elements
                 (public member function) swap swaps the contents
                 (public member function) extract extracts nodes from the container (C++17) (public member function) merge splices nodes from another container (C++17) (public member function)


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


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

Non-member functions

operator== operator!= operator< lexicographically compares the values in the map operator<= (function template) operator> operator>= std::swap(std::map) specializes the std::swap algorithm
                    (function template) erase_if(std::map) Erases all elements satisfying specific criteria (C++20) (function template)

  Deduction guides(since C++17)