std::unordered_map

 

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unordered_map (C++11)

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std::unordered_map

Member types
Member functions
unordered_map::unordered_map unordered_map::~unordered_map unordered_map::operator= unordered_map::get_allocator Iterators unordered_map::beginunordered_map::cbegin unordered_map::endunordered_map::cend Capacity unordered_map::size unordered_map::max_size unordered_map::empty Modifiers unordered_map::clear unordered_map::erase unordered_map::swap unordered_map::extract (C++17) unordered_map::merge (C++17) unordered_map::insert unordered_map::insert_range (C++23) unordered_map::insert_or_assign (C++17)   unordered_map::emplace unordered_map::emplace_hint unordered_map::try_emplace (C++17)	Lookup unordered_map::at unordered_map::operator[] unordered_map::count unordered_map::find unordered_map::contains (C++20) unordered_map::equal_range Bucket interface unordered_map::begin(size_type)unordered_map::cbegin(size_type) unordered_map::end(size_type)unordered_map::cend(size_type) unordered_map::bucket_count unordered_map::max_bucket_count unordered_map::bucket_size unordered_map::bucket Hash policy unordered_map::load_factor unordered_map::max_load_factor unordered_map::rehash unordered_map::reserve Observers unordered_map::hash_function unordered_map::key_eq
Non-member functions
operator==operator!= (until C++20)	std::swap(std::unordered_map) erase_if(std::unordered_map) (C++20)
Deduction guides(C++17)

 

Defined in header <unordered_map>
template<     class Key,     class T,     class Hash = std::hash<Key>,     class KeyEqual = std::equal_to<Key>,     class Allocator = std::allocator< std::pair<const Key, T> > > class unordered_map;		(since C++11)

Unordered map is an associative container that contains key-value pairs with unique keys. Search, insertion, and removal have average constant-time complexity.

std::unordered_map meets the requirements of Template:concept, Template:concept, Template:concept.

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)
hasher	Hash
key_equal	KeyEqual
allocator_type	Allocator
reference	value_type&
const_reference	const value_type&
pointer	std::allocator_traits<Allocator>::pointer
const_pointer	std::allocator_traits<Allocator>::const_pointer
iterator	LegacyForwardIterator to value_type
const_iterator	LegacyForwardIterator to const value_type
local_iterator	An iterator type whose category, value, difference, pointer and reference types are the same as iterator. This iterator can be used to iterate through a single bucket but not across buckets
const_local_iterator	An iterator type whose category, value, difference, pointer and reference types are the same as const_iterator. This iterator can be used to iterate through a single bucket but not across buckets

Member functions

(constructor)	constructs the unordered_map (public member function)
(destructor)	destructs the unordered_map (public member function)
operator=	assigns values to the container (public member function)
get_allocator	returns the associated allocator (public member function)
Iterators
begincbegin	returns an iterator to the beginning (public member function)
endcend	returns an iterator to the end (public member function)
Capacity
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)
Modifiers
clear	clears the contents (public member function)
insert	inserts elements or nodes(since C++17) (public member function)
emplace	constructs element in-place (public member function)
emplace_hint	constructs elements in-place using a hint (public member function)
erase	erases elements (public member function)
swap	swaps the contents (public member function)
Lookup
at	access specified element with bounds checking (public member function)
operator[]	access or insert specified element (public member function)
count	returns the number of elements matching specific key (public member function)
find	finds element with specific key (public member function)
equal_range	returns range of elements matching a specific key (public member function)
Bucket interface
begin(size_type)cbegin(size_type)	returns an iterator to the beginning of the specified bucket (public member function)
end(size_type)cend(size_type)	returns an iterator to the end of the specified bucket (public member function)
bucket_count	returns the number of buckets (public member function)
max_bucket_count	returns the maximum number of buckets (public member function)
bucket_size	returns the number of elements in specific bucket (public member function)
bucket	returns the bucket for specific key (public member function)
Hash policy
load_factor	returns average number of elements per bucket (public member function)
max_load_factor	manages maximum average number of elements per bucket (public member function)
rehash	reserves at least the specified number of buckets and regenerates the hash table (public member function)
reserve	reserves space for at least the specified number of elements and regenerates the hash table (public member function)
Observers
hash_function	returns function used to hash the keys (public member function)
key_eq	returns the function used to compare keys for equality (public member function)

Non-member functions

operator==operator!= (C++11)(C++11)(removed in C++20)	compares the values in the unordered_map (function template)
std::swap(std::unordered_map) (C++11)	specializes the std::swap algorithm (function template)