Standard library header <unordered_map> (C++11)

This header is part of the containers library.

Includes
<compare> (C++20)	Three-way comparison operator support[edit]
<initializer_list> (C++11)	std::initializer_list class template[edit]
Classes
unordered_map (C++11)	collection of key-value pairs, hashed by keys, keys are unique (class template) [edit]
unordered_multimap (C++11)	collection of key-value pairs, hashed by keys (class template) [edit]
Functions
operator==operator!= (C++11)(C++11)(removed in C++20)	compares the values in the unordered_map (function template) [edit]
std::swap(std::unordered_map) (C++11)	specializes the std::swap algorithm (function template) [edit]
erase_if(std::unordered_map) (C++20)	erases all elements satisfying specific criteria (function template) [edit]
operator==operator!= (C++11)(C++11)(removed in C++20)	compares the values in the unordered_multimap (function template) [edit]
std::swap(std::unordered_multimap) (C++11)	specializes the std::swap algorithm (function template) [edit]
erase_if(std::unordered_multimap) (C++20)	erases all elements satisfying specific criteria (function template) [edit]
Range access
begincbegin (C++11)(C++14)	returns an iterator to the beginning of a container or array (function template) [edit]
endcend (C++11)(C++14)	returns an iterator to the end of a container or array (function template) [edit]
rbegincrbegin (C++14)	returns a reverse iterator to the beginning of a container or array (function template) [edit]
rendcrend (C++14)	returns a reverse end iterator for a container or array (function template) [edit]
sizessize (C++17)(C++20)	returns the size of a container or array (function template) [edit]
empty (C++17)	checks whether the container is empty (function template) [edit]
data (C++17)	obtains the pointer to the underlying array (function template) [edit]

Synopsis

#include <compare>
#include <initializer_list>

namespace std {
  // class template unordered_map
  template<class Key,
           class T,
           class Hash = hash<Key>,
           class Pred = equal_to<Key>,
           class Alloc = allocator<pair<const Key, T>>>
  class unordered_map;

  // class template unordered_multimap
  template<class Key,
           class T,
           class Hash = hash<Key>,
           class Pred = equal_to<Key>,
           class Alloc = allocator<pair<const Key, T>>>
  class unordered_multimap;

  template<class Key, class T, class Hash, class Pred, class Alloc>
  constexpr bool operator==(const unordered_map<Key, T, Hash, Pred, Alloc>& a,
                            const unordered_map<Key, T, Hash, Pred, Alloc>& b);

  template<class Key, class T, class Hash, class Pred, class Alloc>
  constexpr bool operator==(const unordered_multimap<Key, T, Hash, Pred, Alloc>& a,
                            const unordered_multimap<Key, T, Hash, Pred, Alloc>& b);

  template<class Key, class T, class Hash, class Pred, class Alloc>
  constexpr void swap(
    unordered_map<Key, T, Hash, Pred, Alloc>& x,
    unordered_map<Key, T, Hash, Pred, Alloc>& y) noexcept(noexcept(x.swap(y)));

  template<class Key, class T, class Hash, class Pred, class Alloc>
  constexpr void swap(
    unordered_multimap<Key, T, Hash, Pred, Alloc>& x,
    unordered_multimap<Key, T, Hash, Pred, Alloc>& y) noexcept(noexcept(x.swap(y)));

  // erasure for unordered_map
  template<class K, class T, class H, class P, class A, class Predicate>
  constexpr typename unordered_map<K, T, H, P, A>::size_type erase_if(
    unordered_map<K, T, H, P, A>& c, Predicate pred);

  // erasure for unordered_multimap
  template<class K, class T, class H, class P, class A, class Predicate>
  constexpr typename unordered_multimap<K, T, H, P, A>::size_type erase_if(
    unordered_multimap<K, T, H, P, A>& c, Predicate pred);

  namespace pmr {
    template<class Key, class T, class Hash = hash<Key>, class Pred = equal_to<Key>>
    using unordered_map =
      std::unordered_map<Key, T, Hash, Pred, polymorphic_allocator<pair<const Key, T>>>;
    template<class Key, class T, class Hash = hash<Key>, class Pred = equal_to<Key>>
    using unordered_multimap = std::
      unordered_multimap<Key, T, Hash, Pred, polymorphic_allocator<pair<const Key, T>>>;

  }
}

Class template std::unordered_map

namespace std {
  template<class Key,
           class T,
           class Hash = hash<Key>,
           class Pred = equal_to<Key>,
           class Allocator = allocator<pair<const Key, T>>>
  class unordered_map
  {
  public:
    // types
    using key_type = Key;
    using mapped_type = T;
    using value_type = pair<const Key, T>;
    using hasher = Hash;
    using key_equal = Pred;
    using allocator_type = Allocator;
    using pointer = allocator_traits<Allocator>::pointer;
    using const_pointer = allocator_traits<Allocator>::const_pointer;
    using reference = value_type&;
    using const_reference = const value_type&;
    using size_type = /* implementation-defined */;
    using difference_type = /* implementation-defined */;

    using iterator = /* implementation-defined */;
    using const_iterator = /* implementation-defined */;
    using local_iterator = /* implementation-defined */;
    using const_local_iterator = /* implementation-defined */;
    using node_type = /* unspecified */;
    using insert_return_type = /*insert-return-type*/<iterator, node_type>;

    // construct/copy/destroy
    constexpr unordered_map();
    constexpr explicit unordered_map(size_type n,
                                     const hasher& hf = hasher(),
                                     const key_equal& eql = key_equal(),
                                     const allocator_type& a = allocator_type());
    template<class InputIter>
    constexpr unordered_map(InputIter f,
                            InputIter l,
                            size_type n = /* see description */,
                            const hasher& hf = hasher(),
                            const key_equal& eql = key_equal(),
                            const allocator_type& a = allocator_type());

    template<container-compatible-range<value_type> R>
    constexpr unordered_map(from_range_t,
                            R&& rg,
                            size_type n = /* see description */,
                            const hasher& hf = hasher(),
                            const key_equal& eql = key_equal(),
                            const allocator_type& a = allocator_type());
    constexpr unordered_map(const unordered_map&);
    constexpr unordered_map(unordered_map&&);
    constexpr explicit unordered_map(const Allocator&);
    constexpr unordered_map(const unordered_map&, const type_identity_t<Allocator>&);
    constexpr unordered_map(unordered_map&&, const type_identity_t<Allocator>&);
    constexpr unordered_map(initializer_list<value_type> il,
                            size_type n = /* see description */,
                            const hasher& hf = hasher(),
                            const key_equal& eql = key_equal(),
                            const allocator_type& a = allocator_type());
    constexpr unordered_map(size_type n, const allocator_type& a)
      : unordered_map(n, hasher(), key_equal(), a)
    {
    }
    constexpr unordered_map(size_type n, const hasher& hf, const allocator_type& a)
      : unordered_map(n, hf, key_equal(), a)
    {
    }
    template<class InputIter>
    constexpr unordered_map(InputIter f,
                            InputIter l,
                            size_type n,
                            const allocator_type& a)
      : unordered_map(f, l, n, hasher(), key_equal(), a)
    {
    }
    template<class InputIter>
    constexpr unordered_map(
      InputIter f, InputIter l, size_type n, const hasher& hf, const allocator_type& a)
      : unordered_map(f, l, n, hf, key_equal(), a)
    {
    }
    template<container-compatible-range<value_type> R>
    constexpr unordered_map(from_range_t, R&& rg, size_type n, const allocator_type& a)
      : unordered_map(from_range, std::forward<R>(rg), n, hasher(), key_equal(), a)
    {
    }
    template<container-compatible-range<value_type> R>
    constexpr unordered_map(
      from_range_t, R&& rg, size_type n, const hasher& hf, const allocator_type& a)
      : unordered_map(from_range, std::forward<R>(rg), n, hf, key_equal(), a)
    {
    }
    constexpr unordered_map(initializer_list<value_type> il,
                            size_type n,
                            const allocator_type& a)
      : unordered_map(il, n, hasher(), key_equal(), a)
    {
    }
    constexpr unordered_map(initializer_list<value_type> il,
                            size_type n,
                            const hasher& hf,
                            const allocator_type& a)
      : unordered_map(il, n, hf, key_equal(), a)
    {
    }
    constexpr ~unordered_map();
    constexpr unordered_map& operator=(const unordered_map&);
    constexpr unordered_map& operator=(unordered_map&&) noexcept(
      allocator_traits<Allocator>::is_always_equal::value&&
        is_nothrow_move_assignable_v<Hash>&& is_nothrow_move_assignable_v<Pred>);
    constexpr unordered_map& operator=(initializer_list<value_type>);
    constexpr allocator_type get_allocator() const noexcept;

    // iterators
    constexpr iterator begin() noexcept;
    constexpr const_iterator begin() const noexcept;
    constexpr iterator end() noexcept;
    constexpr const_iterator end() const noexcept;
    constexpr const_iterator cbegin() const noexcept;
    constexpr const_iterator cend() const noexcept;

    // capacity
    constexpr bool empty() const noexcept;
    constexpr size_type size() const noexcept;
    constexpr size_type max_size() const noexcept;

    // modifiers
    template<class... Args> constexpr pair<iterator, bool> emplace(Args&&... args);
    template<class... Args>
    constexpr iterator emplace_hint(const_iterator position, Args&&... args);
    constexpr pair<iterator, bool> insert(const value_type& obj);
    constexpr pair<iterator, bool> insert(value_type&& obj);
    template<class P> constexpr pair<iterator, bool> insert(P&& obj);
    constexpr iterator insert(const_iterator hint, const value_type& obj);
    constexpr iterator insert(const_iterator hint, value_type&& obj);
    template<class P> constexpr iterator insert(const_iterator hint, P&& obj);
    template<class InputIter> constexpr void insert(InputIter first, InputIter last);
    template<container-compatible-range<value_type> R>
    constexpr void insert_range(R&& rg);
    constexpr void insert(initializer_list<value_type>);

    constexpr node_type extract(const_iterator position);
    constexpr node_type extract(const key_type& x);
    template<class K> constexpr node_type extract(K&& x);
    constexpr insert_return_type insert(node_type&& nh);
    constexpr iterator insert(const_iterator hint, node_type&& nh);

    template<class... Args>
    constexpr pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
    template<class... Args>
    constexpr pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
    template<class K, class... Args>
    constexpr pair<iterator, bool> try_emplace(K&& k, Args&&... args);
    template<class... Args>
    constexpr iterator try_emplace(const_iterator hint,
                                   const key_type& k,
                                   Args&&... args);
    template<class... Args>
    constexpr iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
    template<class K, class... Args>
    constexpr iterator try_emplace(const_iterator hint, K&& k, Args&&... args);
    template<class M>
    constexpr pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
    template<class M>
    constexpr pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
    template<class K, class M>
    constexpr pair<iterator, bool> insert_or_assign(K&& k, M&& obj);
    template<class M>
    constexpr iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
    template<class M>
    constexpr iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
    template<class K, class M>
    constexpr iterator insert_or_assign(const_iterator hint, K&& k, M&& obj);

    constexpr iterator erase(iterator position);
    constexpr iterator erase(const_iterator position);
    constexpr size_type erase(const key_type& k);
    template<class K> constexpr size_type erase(K&& x);
    constexpr iterator erase(const_iterator first, const_iterator last);
    constexpr void swap(unordered_map&) noexcept(
      allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_swappable_v<Hash>&&
        is_nothrow_swappable_v<Pred>);
    constexpr void clear() noexcept;

    template<class H2, class P2>
    constexpr void merge(unordered_map<Key, T, H2, P2, Allocator>& source);
    template<class H2, class P2>
    constexpr void merge(unordered_map<Key, T, H2, P2, Allocator>&& source);
    template<class H2, class P2>
    constexpr void merge(unordered_multimap<Key, T, H2, P2, Allocator>& source);
    template<class H2, class P2>
    constexpr void merge(unordered_multimap<Key, T, H2, P2, Allocator>&& source);

    // observers
    constexpr hasher hash_function() const;
    constexpr key_equal key_eq() const;

    // map operations
    constexpr iterator find(const key_type& k);
    constexpr const_iterator find(const key_type& k) const;
    template<class K> constexpr iterator find(const K& k);
    template<class K> constexpr const_iterator find(const K& k) const;
    constexpr size_type count(const key_type& k) const;
    template<class K> constexpr size_type count(const K& k) const;
    constexpr bool contains(const key_type& k) const;
    template<class K> constexpr bool contains(const K& k) const;
    constexpr pair<iterator, iterator> equal_range(const key_type& k);
    constexpr pair<const_iterator, const_iterator> equal_range(const key_type& k) const;
    template<class K> constexpr pair<iterator, iterator> equal_range(const K& k);
    template<class K>
    constexpr pair<const_iterator, const_iterator> equal_range(const K& k) const;

    // element access
    constexpr mapped_type& operator[](const key_type& k);
    constexpr mapped_type& operator[](key_type&& k);
    template<class K> constexpr mapped_type& operator[](K&& k);
    constexpr mapped_type& at(const key_type& k);
    constexpr const mapped_type& at(const key_type& k) const;
    template<class K> constexpr mapped_type& at(const K& k);
    template<class K> constexpr const mapped_type& at(const K& k) const;

    // bucket interface
    constexpr size_type bucket_count() const noexcept;
    constexpr size_type max_bucket_count() const noexcept;
    constexpr size_type bucket_size(size_type n) const;
    constexpr size_type bucket(const key_type& k) const;
    template<class K> constexpr size_type bucket(const K& k) const;
    constexpr local_iterator begin(size_type n);
    constexpr const_local_iterator begin(size_type n) const;
    constexpr local_iterator end(size_type n);
    constexpr const_local_iterator end(size_type n) const;
    constexpr const_local_iterator cbegin(size_type n) const;
    constexpr const_local_iterator cend(size_type n) const;

    // hash policy
    constexpr float load_factor() const noexcept;
    constexpr float max_load_factor() const noexcept;
    constexpr void max_load_factor(float z);
    constexpr void rehash(size_type n);
    constexpr void reserve(size_type n);
  };

  template<class InputIter,
           class Hash = hash</*iter-key-type*/<InputIter>>,
           class Pred = equal_to</*iter-key-type*/<InputIter>>,
           class Allocator = allocator</*iter-to-alloc-type*/<InputIter>>>
  unordered_map(InputIter,
                InputIter,
                typename /* see description */ ::size_type = /* see description */,
                Hash = Hash(),
                Pred = Pred(),
                Allocator = Allocator()) -> unordered_map</*iter-key-type*/<InputIter>,
                                                          /*iter-mapped-type*/<InputIter>,
                                                          Hash,
                                                          Pred,
                                                          Allocator>;

  template<ranges::input_range R,
           class Hash = hash</*range-key-type*/<R>>,
           class Pred = equal_to</*range-key-type*/<R>>,
           class Allocator = allocator</*range-to-alloc-type*/<R>>>
  unordered_map(from_range_t,
                R&&,
                typename /* see description */ ::size_type = /* see description */,
                Hash = Hash(),
                Pred = Pred(),
                Allocator = Allocator()) -> unordered_map</*range-key-type*/<R>,
                                                          /*range-mapped-type*/<R>,
                                                          Hash,
                                                          Pred,
                                                          Allocator>;

  template<class Key,
           class T,
           class Hash = hash<Key>,
           class Pred = equal_to<Key>,
           class Allocator = allocator<pair<const Key, T>>>
  unordered_map(initializer_list<pair<Key, T>>,
                typename /* see description */ ::size_type = /* see description */,
                Hash = Hash(),
                Pred = Pred(),
                Allocator = Allocator()) -> unordered_map<Key, T, Hash, Pred, Allocator>;

  template<class InputIter, class Allocator>
  unordered_map(InputIter,
                InputIter,
                typename /* see description */ ::size_type,
                Allocator) -> unordered_map</*iter-key-type*/<InputIter>,
                                            /*iter-mapped-type*/<InputIter>,
                                            hash</*iter-key-type*/<InputIter>>,
                                            equal_to</*iter-key-type*/<InputIter>>,
                                            Allocator>;

  template<class InputIter, class Allocator>
  unordered_map(InputIter, InputIter, Allocator)
    -> unordered_map</*iter-key-type*/<InputIter>,
                     /*iter-mapped-type*/<InputIter>,
                     hash</*iter-key-type*/<InputIter>>,
                     equal_to</*iter-key-type*/<InputIter>>,
                     Allocator>;

  template<class InputIter, class Hash, class Allocator>
  unordered_map(
    InputIter, InputIter, typename /* see description */ ::size_type, Hash, Allocator)
    -> unordered_map</*iter-key-type*/<InputIter>,
                     /*iter-mapped-type*/<InputIter>,
                     Hash,
                     equal_to</*iter-key-type*/<InputIter>>,
                     Allocator>;

  template<ranges::input_range R, class Allocator>
  unordered_map(from_range_t, R&&, typename /* see description */ ::size_type, Allocator)
    -> unordered_map</*range-key-type*/<R>,
                     /*range-mapped-type*/<R>,
                     hash</*range-key-type*/<R>>,
                     equal_to</*range-key-type*/<R>>,
                     Allocator>;

  template<ranges::input_range R, class Allocator>
  unordered_map(from_range_t, R&&, Allocator)
    -> unordered_map</*range-key-type*/<R>,
                     /*range-mapped-type*/<R>,
                     hash</*range-key-type*/<R>>,
                     equal_to</*range-key-type*/<R>>,
                     Allocator>;

  template<ranges::input_range R, class Hash, class Allocator>
  unordered_map(
    from_range_t, R&&, typename /* see description */ ::size_type, Hash, Allocator)
    -> unordered_map</*range-key-type*/<R>,
                     /*range-mapped-type*/<R>,
                     Hash,
                     equal_to</*range-key-type*/<R>>,
                     Allocator>;

  template<class Key, class T, class Allocator>
  unordered_map(initializer_list<pair<Key, T>>,
                typename /* see description */ ::size_type,
                Allocator) -> unordered_map<Key, T, hash<Key>, equal_to<Key>, Allocator>;

  template<class Key, class T, class Allocator>
  unordered_map(initializer_list<pair<Key, T>>, Allocator)
    -> unordered_map<Key, T, hash<Key>, equal_to<Key>, Allocator>;

  template<class Key, class T, class Hash, class Allocator>
  unordered_map(initializer_list<pair<Key, T>>,
                typename /* see description */ ::size_type,
                Hash,
                Allocator) -> unordered_map<Key, T, Hash, equal_to<Key>, Allocator>;
}

Class template std::unordered_multimap

namespace std {
  template<class Key,
           class T,
           class Hash = hash<Key>,
           class Pred = equal_to<Key>,
           class Allocator = allocator<pair<const Key, T>>>
  class unordered_multimap
  {
  public:
    // types
    using key_type = Key;
    using mapped_type = T;
    using value_type = pair<const Key, T>;
    using hasher = Hash;
    using key_equal = Pred;
    using allocator_type = Allocator;
    using pointer = allocator_traits<Allocator>::pointer;
    using const_pointer = allocator_traits<Allocator>::const_pointer;
    using reference = value_type&;
    using const_reference = const value_type&;
    using size_type = /* implementation-defined */;
    using difference_type = /* implementation-defined */;

    using iterator = /* implementation-defined */;
    using const_iterator = /* implementation-defined */;
    using local_iterator = /* implementation-defined */;
    using const_local_iterator = /* implementation-defined */;
    using node_type = /* unspecified */;

    // construct/copy/destroy
    constexpr unordered_multimap();
    constexpr explicit unordered_multimap(size_type n,
                                          const hasher& hf = hasher(),
                                          const key_equal& eql = key_equal(),
                                          const allocator_type& a = allocator_type());
    template<class InputIter>
    constexpr unordered_multimap(InputIter f,
                                 InputIter l,
                                 size_type n = /* see description */,
                                 const hasher& hf = hasher(),
                                 const key_equal& eql = key_equal(),
                                 const allocator_type& a = allocator_type());
    template<container-compatible-range<value_type> R>
    constexpr unordered_multimap(from_range_t,
                                 R&& rg,
                                 size_type n = /* see description */,
                                 const hasher& hf = hasher(),
                                 const key_equal& eql = key_equal(),
                                 const allocator_type& a = allocator_type());
    constexpr unordered_multimap(const unordered_multimap&);
    constexpr unordered_multimap(unordered_multimap&&);
    constexpr explicit unordered_multimap(const Allocator&);
    constexpr unordered_multimap(const unordered_multimap&,
                                 const type_identity_t<Allocator>&);
    constexpr unordered_multimap(unordered_multimap&&, const type_identity_t<Allocator>&);
    constexpr unordered_multimap(initializer_list<value_type> il,
                                 size_type n = /* see description */,
                                 const hasher& hf = hasher(),
                                 const key_equal& eql = key_equal(),
                                 const allocator_type& a = allocator_type());
    constexpr unordered_multimap(size_type n, const allocator_type& a)
      : unordered_multimap(n, hasher(), key_equal(), a)
    {
    }
    constexpr unordered_multimap(size_type n, const hasher& hf, const allocator_type& a)
      : unordered_multimap(n, hf, key_equal(), a)
    {
    }
    template<class InputIter>
    constexpr unordered_multimap(InputIter f,
                                 InputIter l,
                                 size_type n,
                                 const allocator_type& a)
      : unordered_multimap(f, l, n, hasher(), key_equal(), a)
    {
    }
    template<class InputIter>
    constexpr unordered_multimap(
      InputIter f, InputIter l, size_type n, const hasher& hf, const allocator_type& a)
      : unordered_multimap(f, l, n, hf, key_equal(), a)
    {
    }
    template<container-compatible-range<value_type> R>
    constexpr unordered_multimap(from_range_t,
                                 R&& rg,
                                 size_type n,
                                 const allocator_type& a)
      : unordered_multimap(from_range, std::forward<R>(rg), n, hasher(), key_equal(), a)
    {
    }
    template<container-compatible-range<value_type> R>
    constexpr unordered_multimap(
      from_range_t, R&& rg, size_type n, const hasher& hf, const allocator_type& a)
      : unordered_multimap(from_range, std::forward<R>(rg), n, hf, key_equal(), a)
    {
    }
    constexpr unordered_multimap(initializer_list<value_type> il,
                                 size_type n,
                                 const allocator_type& a)
      : unordered_multimap(il, n, hasher(), key_equal(), a)
    {
    }
    constexpr unordered_multimap(initializer_list<value_type> il,
                                 size_type n,
                                 const hasher& hf,
                                 const allocator_type& a)
      : unordered_multimap(il, n, hf, key_equal(), a)
    {
    }
    constexpr ~unordered_multimap();
    constexpr unordered_multimap& operator=(const unordered_multimap&);
    constexpr unordered_multimap& operator=(unordered_multimap&&) noexcept(
      allocator_traits<Allocator>::is_always_equal::value&&
        is_nothrow_move_assignable_v<Hash>&& is_nothrow_move_assignable_v<Pred>);
    constexpr unordered_multimap& operator=(initializer_list<value_type>);
    constexpr allocator_type get_allocator() const noexcept;

    // iterators
    constexpr iterator begin() noexcept;
    constexpr const_iterator begin() const noexcept;
    constexpr iterator end() noexcept;
    constexpr const_iterator end() const noexcept;
    constexpr const_iterator cbegin() const noexcept;
    constexpr const_iterator cend() const noexcept;

    // capacity
    constexpr bool empty() const noexcept;
    constexpr size_type size() const noexcept;
    constexpr size_type max_size() const noexcept;

    // modifiers
    template<class... Args> constexpr iterator emplace(Args&&... args);
    template<class... Args>
    constexpr iterator emplace_hint(const_iterator position, Args&&... args);
    constexpr iterator insert(const value_type& obj);
    constexpr iterator insert(value_type&& obj);
    template<class P> constexpr iterator insert(P&& obj);
    constexpr iterator insert(const_iterator hint, const value_type& obj);
    constexpr iterator insert(const_iterator hint, value_type&& obj);
    template<class P> constexpr iterator insert(const_iterator hint, P&& obj);
    template<class InputIter> constexpr void insert(InputIter first, InputIter last);
    template<container-compatible-range<value_type> R>
    constexpr void insert_range(R&& rg);
    constexpr void insert(initializer_list<value_type>);

    constexpr node_type extract(const_iterator position);
    constexpr node_type extract(const key_type& x);
    template<class K> constexpr node_type extract(K&& x);
    constexpr iterator insert(node_type&& nh);
    constexpr iterator insert(const_iterator hint, node_type&& nh);

    constexpr iterator erase(iterator position);
    constexpr iterator erase(const_iterator position);
    constexpr size_type erase(const key_type& k);
    template<class K> constexpr size_type erase(K&& x);
    constexpr iterator erase(const_iterator first, const_iterator last);
    constexpr void swap(unordered_multimap&) noexcept(
      allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_swappable_v<Hash>&&
        is_nothrow_swappable_v<Pred>);
    constexpr void clear() noexcept;

    template<class H2, class P2>
    constexpr void merge(unordered_multimap<Key, T, H2, P2, Allocator>& source);
    template<class H2, class P2>
    constexpr void merge(unordered_multimap<Key, T, H2, P2, Allocator>&& source);
    template<class H2, class P2>
    constexpr void merge(unordered_map<Key, T, H2, P2, Allocator>& source);
    template<class H2, class P2>
    constexpr void merge(unordered_map<Key, T, H2, P2, Allocator>&& source);

    // observers
    constexpr hasher hash_function() const;
    constexpr key_equal key_eq() const;

    // map operations
    constexpr iterator find(const key_type& k);
    constexpr const_iterator find(const key_type& k) const;
    template<class K> constexpr iterator find(const K& k);
    template<class K> constexpr const_iterator find(const K& k) const;
    constexpr size_type count(const key_type& k) const;
    template<class K> constexpr size_type count(const K& k) const;
    constexpr bool contains(const key_type& k) const;
    template<class K> constexpr bool contains(const K& k) const;
    constexpr pair<iterator, iterator> equal_range(const key_type& k);
    constexpr pair<const_iterator, const_iterator> equal_range(const key_type& k) const;
    template<class K> constexpr pair<iterator, iterator> equal_range(const K& k);
    template<class K>
    constexpr pair<const_iterator, const_iterator> equal_range(const K& k) const;

    // bucket interface
    constexpr size_type bucket_count() const noexcept;
    constexpr size_type max_bucket_count() const noexcept;
    constexpr size_type bucket_size(size_type n) const;
    constexpr size_type bucket(const key_type& k) const;
    template<class K> constexpr size_type bucket(const K& k) const;
    constexpr local_iterator begin(size_type n);
    constexpr const_local_iterator begin(size_type n) const;
    constexpr local_iterator end(size_type n);
    constexpr const_local_iterator end(size_type n) const;
    constexpr const_local_iterator cbegin(size_type n) const;
    constexpr const_local_iterator cend(size_type n) const;

    // hash policy
    constexpr float load_factor() const noexcept;
    constexpr float max_load_factor() const noexcept;
    constexpr void max_load_factor(float z);
    constexpr void rehash(size_type n);
    constexpr void reserve(size_type n);
  };

  template<class InputIter,
           class Hash = hash</*iter-key-type*/<InputIter>>,
           class Pred = equal_to</*iter-key-type*/<InputIter>>,
           class Allocator = allocator</*iter-to-alloc-type*/<InputIter>>>
  unordered_multimap(InputIter,
                     InputIter,
                     typename /* see description */ ::size_type = /* see description */,
                     Hash = Hash(),
                     Pred = Pred(),
                     Allocator = Allocator())
    -> unordered_multimap</*iter-key-type*/<InputIter>,
                          /*iter-mapped-type*/<InputIter>,
                          Hash,
                          Pred,
                          Allocator>;

  template<ranges::input_range R,
           class Hash = hash</*range-key-type*/<R>>,
           class Pred = equal_to</*range-key-type*/<R>>,
           class Allocator = allocator</*range-to-alloc-type*/<R>>>
  unordered_multimap(from_range_t,
                     R&&,
                     typename /* see description */ ::size_type = /* see description */,
                     Hash = Hash(),
                     Pred = Pred(),
                     Allocator = Allocator())
    -> unordered_multimap</*range-key-type*/<R>,
                          /*range-mapped-type*/<R>,
                          Hash,
                          Pred,
                          Allocator>;

  template<class Key,
           class T,
           class Hash = hash<Key>,
           class Pred = equal_to<Key>,
           class Allocator = allocator<pair<const Key, T>>>
  unordered_multimap(initializer_list<pair<Key, T>>,
                     typename /* see description */ ::size_type = /* see description */,
                     Hash = Hash(),
                     Pred = Pred(),
                     Allocator = Allocator())
    -> unordered_multimap<Key, T, Hash, Pred, Allocator>;

  template<class InputIter, class Allocator>
  unordered_multimap(InputIter,
                     InputIter,
                     typename /* see description */ ::size_type,
                     Allocator)
    -> unordered_multimap</*iter-key-type*/<InputIter>,
                          /*iter-mapped-type*/<InputIter>,
                          hash</*iter-key-type*/<InputIter>>,
                          equal_to</*iter-key-type*/<InputIter>>,
                          Allocator>;

  template<class InputIter, class Allocator>
  unordered_multimap(InputIter, InputIter, Allocator)
    -> unordered_multimap</*iter-key-type*/<InputIter>,
                          /*iter-mapped-type*/<InputIter>,
                          hash</*iter-key-type*/<InputIter>>,
                          equal_to</*iter-key-type*/<InputIter>>,
                          Allocator>;

  template<class InputIter, class Hash, class Allocator>
  unordered_multimap(
    InputIter, InputIter, typename /* see description */ ::size_type, Hash, Allocator)
    -> unordered_multimap</*iter-key-type*/<InputIter>,
                          /*iter-mapped-type*/<InputIter>,
                          Hash,
                          equal_to</*iter-key-type*/<InputIter>>,
                          Allocator>;

  template<ranges::input_range R, class Allocator>
  unordered_multimap(from_range_t,
                     R&&,
                     typename /* see description */ ::size_type,
                     Allocator) -> unordered_multimap</*range-key-type*/<R>,
                                                      /*range-mapped-type*/<R>,
                                                      hash</*range-key-type*/<R>>,
                                                      equal_to</*range-key-type*/<R>>,
                                                      Allocator>;

  template<ranges::input_range R, class Allocator>
  unordered_multimap(from_range_t, R&&, Allocator)
    -> unordered_multimap</*range-key-type*/<R>,
                          /*range-mapped-type*/<R>,
                          hash</*range-key-type*/<R>>,
                          equal_to</*range-key-type*/<R>>,
                          Allocator>;

  template<ranges::input_range R, class Hash, class Allocator>
  unordered_multimap(
    from_range_t, R&&, typename /* see description */ ::size_type, Hash, Allocator)
    -> unordered_multimap</*range-key-type*/<R>,
                          /*range-mapped-type*/<R>,
                          Hash,
                          equal_to</*range-key-type*/<R>>,
                          Allocator>;

  template<class Key, class T, class Allocator>
  unordered_multimap(initializer_list<pair<Key, T>>,
                     typename /* see description */ ::size_type,
                     Allocator)
    -> unordered_multimap<Key, T, hash<Key>, equal_to<Key>, Allocator>;

  template<class Key, class T, class Allocator>
  unordered_multimap(initializer_list<pair<Key, T>>, Allocator)
    -> unordered_multimap<Key, T, hash<Key>, equal_to<Key>, Allocator>;

  template<class Key, class T, class Hash, class Allocator>
  unordered_multimap(initializer_list<pair<Key, T>>,
                     typename /* see description */ ::size_type,
                     Hash,
                     Allocator)
    -> unordered_multimap<Key, T, Hash, equal_to<Key>, Allocator>;
}

Standard library header <unordered_map> (C++11)

Includes

Classes

Functions

Range access

Synopsis

Class template std::unordered_map

Class template std::unordered_multimap