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Difference between revisions of "cpp/header/unordered map"

From cppreference.com
< cpp‎ | header
m (updated per current draft, C++23 changes: rangification, +range functions, ctors, +DG, allocators, -swap)
(move synopsis to template)
 
Line 29: Line 29:
  
 
===Synopsis===
 
===Synopsis===
−
{{source|1=
+
{{cpp/synopsis/unordered_map}}
−
#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>
+
−
    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>
+
−
    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>
+
−
    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>
+
−
    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>
+
−
    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>
+
−
    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,
+
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                                polymorphic_allocator<pair<const Key, T>>>;
+
−
 
+
−
  }
+
−
}
+
−
}}
+
−
 
+
−
====Class template {{lc|std::unordered_map}}====
+
−
{{source|1=
+
−
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              = typename allocator_traits<Allocator>::pointer;
+
−
    using const_pointer        = typename 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
+
−
    unordered_map();
+
−
    explicit unordered_map(size_type n,
+
−
                          const hasher& hf = hasher(),
+
−
                          const key_equal& eql = key_equal(),
+
−
                          const allocator_type& a = allocator_type());
+
−
    template<class InputIt>
+
−
      unordered_map(InputIt f, InputIt 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>
+
−
      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());
+
−
    unordered_map(const unordered_map&);
+
−
    unordered_map(unordered_map&&);
+
−
    explicit unordered_map(const Allocator&);
+
−
    unordered_map(const unordered_map&, const type_identity_t<Allocator>&);
+
−
    unordered_map(unordered_map&&, const type_identity_t<Allocator>&);
+
−
    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());
+
−
    unordered_map(size_type n, const allocator_type& a)
+
−
      : unordered_map(n, hasher(), key_equal(), a) { }
+
−
    unordered_map(size_type n, const hasher& hf, const allocator_type& a)
+
−
      : unordered_map(n, hf, key_equal(), a) { }
+
−
    template<class InputIt>
+
−
      unordered_map(InputIt f, InputIt l, size_type n, const allocator_type& a)
+
−
        : unordered_map(f, l, n, hasher(), key_equal(), a) { }
+
−
    template<class InputIt>
+
−
      unordered_map(InputIt f, InputIt 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>
+
−
      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>
+
−
      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) { }
+
−
    unordered_map(initializer_list<value_type> il, size_type n, const allocator_type& a)
+
−
      : unordered_map(il, n, hasher(), key_equal(), a) { }
+
−
    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) { }
+
−
    ~unordered_map();
+
−
    unordered_map& operator=(const unordered_map&);
+
−
    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>);
+
−
    unordered_map& operator=(initializer_list<value_type>);
+
−
    allocator_type get_allocator() const noexcept;
+
−
 
+
−
    // iterators
+
−
    iterator      begin() noexcept;
+
−
    const_iterator begin() const noexcept;
+
−
    iterator      end() noexcept;
+
−
    const_iterator end() const noexcept;
+
−
    const_iterator cbegin() const noexcept;
+
−
    const_iterator cend() const noexcept;
+
−
 
+
−
    // capacity
+
−
    [[nodiscard]] bool empty() const noexcept;
+
−
    size_type size() const noexcept;
+
−
    size_type max_size() const noexcept;
+
−
 
+
−
    // modifiers
+
−
    template<class... Args> pair<iterator, bool> emplace(Args&&... args);
+
−
    template<class... Args> iterator emplace_hint(const_iterator position,
+
−
                                                  Args&&... args);
+
−
    pair<iterator, bool> insert(const value_type& obj);
+
−
    pair<iterator, bool> insert(value_type&& obj);
+
−
    template<class P> pair<iterator, bool> insert(P&& obj);
+
−
    iterator      insert(const_iterator hint, const value_type& obj);
+
−
    iterator      insert(const_iterator hint, value_type&& obj);
+
−
    template<class P> iterator insert(const_iterator hint, P&& obj);
+
−
    template<class InputIt> void insert(InputIt first, InputIt last);
+
−
    template<__container_compatible_range<value_type> R>
+
−
      void insert_range(R&& rg);
+
−
    void insert(initializer_list<value_type>);
+
−
 
+
−
    node_type extract(const_iterator position);
+
−
    node_type extract(const key_type& x);
+
−
    template<class K> node_type extract(K&& x);
+
−
    insert_return_type insert(node_type&& nh);
+
−
    iterator          insert(const_iterator hint, node_type&& nh);
+
−
 
+
−
    template<class... Args>
+
−
      pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
+
−
    template<class... Args>
+
−
      pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
+
−
    template<class... Args>
+
−
      iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);
+
−
    template<class... Args>
+
−
      iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
+
−
    template<class M>
+
−
      pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
+
−
    template<class M>
+
−
      pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
+
−
    template<class M>
+
−
      iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
+
−
    template<class M>
+
−
      iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
+
−
 
+
−
    iterator  erase(iterator position);
+
−
    iterator  erase(const_iterator position);
+
−
    size_type erase(const key_type& k);
+
−
    template<class K> size_type erase(K&& x);
+
−
    iterator  erase(const_iterator first, const_iterator last);
+
−
    void      swap(unordered_map&)
+
−
      noexcept(allocator_traits<Allocator>::is_always_equal::value &&
+
−
              is_nothrow_swappable_v<Hash> &&
+
−
              is_nothrow_swappable_v<Pred>);
+
−
    void      clear() noexcept;
+
−
 
+
−
    template<class H2, class P2>
+
−
      void merge(unordered_map<Key, T, H2, P2, Allocator>& source);
+
−
    template<class H2, class P2>
+
−
      void merge(unordered_map<Key, T, H2, P2, Allocator>&& source);
+
−
    template<class H2, class P2>
+
−
      void merge(unordered_multimap<Key, T, H2, P2, Allocator>& source);
+
−
    template<class H2, class P2>
+
−
      void merge(unordered_multimap<Key, T, H2, P2, Allocator>&& source);
+
−
 
+
−
    // observers
+
−
    hasher hash_function() const;
+
−
    key_equal key_eq() const;
+
−
 
+
−
    // map operations
+
−
    iterator        find(const key_type& k);
+
−
    const_iterator  find(const key_type& k) const;
+
−
    template<class K>
+
−
      iterator      find(const K& k);
+
−
    template<class K>
+
−
      const_iterator find(const K& k) const;
+
−
    template<class K>
+
−
    size_type        count(const key_type& k) const;
+
−
    template<class K>
+
−
      size_type      count(const K& k) const;
+
−
    bool            contains(const key_type& k) const;
+
−
    template<class K>
+
−
      bool          contains(const K& k) const;
+
−
    pair<iterator, iterator>              equal_range(const key_type& k);
+
−
    pair<const_iterator, const_iterator>  equal_range(const key_type& k) const;
+
−
    template<class K>
+
−
      pair<iterator, iterator>            equal_range(const K& k);
+
−
    template<class K>
+
−
      pair<const_iterator, const_iterator> equal_range(const K& k) const;
+
−
 
+
−
    // element access
+
−
    mapped_type& operator[](const key_type& k);
+
−
    mapped_type& operator[](key_type&& k);
+
−
    mapped_type& at(const key_type& k);
+
−
    const mapped_type& at(const key_type& k) const;
+
−
 
+
−
    // bucket interface
+
−
    size_type bucket_count() const noexcept;
+
−
    size_type max_bucket_count() const noexcept;
+
−
    size_type bucket_size(size_type n) const;
+
−
    size_type bucket(const key_type& k) const;
+
−
    local_iterator begin(size_type n);
+
−
    const_local_iterator begin(size_type n) const;
+
−
    local_iterator end(size_type n);
+
−
    const_local_iterator end(size_type n) const;
+
−
    const_local_iterator cbegin(size_type n) const;
+
−
    const_local_iterator cend(size_type n) const;
+
−
 
+
−
    // hash policy
+
−
    float load_factor() const noexcept;
+
−
    float max_load_factor() const noexcept;
+
−
    void max_load_factor(float z);
+
−
    void rehash(size_type n);
+
−
    void reserve(size_type n);
+
−
  };
+
−
 
+
−
  template<class InputIt,
+
−
          class Hash = hash<__iter_key_type<InputIt>>,
+
−
          class Pred = equal_to<__iter_key_type<InputIt>>,
+
−
          class Allocator = allocator<__iter_to_alloc_type<InputIt>>>
+
−
    unordered_map(InputIt, InputIt,
+
−
                  typename /* see description */::size_type = /* see description */,
+
−
                  Hash = Hash(), Pred = Pred(), Allocator = Allocator())
+
−
      -> unordered_map<__iter_key_type<InputIt>, __iter_mapped_type<InputIt>, 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 InputIt, class Allocator>
+
−
    unordered_map(InputIt, InputIt, typename /* see description */::size_type, Allocator)
+
−
      -> unordered_map<__iter_key_type<InputIt>, __iter_mapped_type<InputIt>,
+
−
                      hash<__iter_key_type<InputIt>>,
+
−
                      equal_to<__iter_key_type<InputIt>>, Allocator>;
+
−
 
+
−
  template<class InputIt, class Allocator>
+
−
    unordered_map(InputIt, InputIt, Allocator)
+
−
      -> unordered_map<__iter_key_type<InputIt>, __iter_mapped_type<InputIt>,
+
−
                      hash<__iter_key_type<InputIt>>,
+
−
                      equal_to<__iter_key_type<InputIt>>, Allocator>;
+
−
 
+
−
  template<class InputIt, class Hash, class Allocator>
+
−
    unordered_map(InputIt, InputIt, typename /* see description */::size_type, Hash,
+
−
                  Allocator)
+
−
      -> unordered_map<__iter_key_type<InputIt>, __iter_mapped_type<InputIt>, Hash,
+
−
                      equal_to<__iter_key_type<InputIt>>, 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 {{lc|std::unordered_multimap}}====
+
−
{{source|1=
+
−
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              = typename allocator_traits<Allocator>::pointer;
+
−
    using const_pointer        = typename 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
+
−
    unordered_multimap();
+
−
    explicit unordered_multimap(size_type n,
+
−
                                const hasher& hf = hasher(),
+
−
                                const key_equal& eql = key_equal(),
+
−
                                const allocator_type& a = allocator_type());
+
−
    template<class InputIt>
+
−
      unordered_multimap(InputIt f, InputIt 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>
+
−
      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());
+
−
    unordered_multimap(const unordered_multimap&);
+
−
    unordered_multimap(unordered_multimap&&);
+
−
    explicit unordered_multimap(const Allocator&);
+
−
    unordered_multimap(const unordered_multimap&, const type_identity_t<Allocator>&);
+
−
    unordered_multimap(unordered_multimap&&, const type_identity_t<Allocator>&);
+
−
    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());
+
−
    unordered_multimap(size_type n, const allocator_type& a)
+
−
      : unordered_multimap(n, hasher(), key_equal(), a) { }
+
−
    unordered_multimap(size_type n, const hasher& hf, const allocator_type& a)
+
−
      : unordered_multimap(n, hf, key_equal(), a) { }
+
−
    template<class InputIt>
+
−
      unordered_multimap(InputIt f, InputIt l, size_type n, const allocator_type& a)
+
−
        : unordered_multimap(f, l, n, hasher(), key_equal(), a) { }
+
−
    template<class InputIt>
+
−
      unordered_multimap(InputIt f, InputIt 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>
+
−
    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>
+
−
    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) { }
+
−
    unordered_multimap(initializer_list<value_type> il, size_type n,
+
−
                      const allocator_type& a)
+
−
      : unordered_multimap(il, n, hasher(), key_equal(), a) { }
+
−
    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) { }
+
−
    ~unordered_multimap();
+
−
    unordered_multimap& operator=(const unordered_multimap&);
+
−
    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>);
+
−
    unordered_multimap& operator=(initializer_list<value_type>);
+
−
    allocator_type get_allocator() const noexcept;
+
−
 
+
−
    // iterators
+
−
    iterator      begin() noexcept;
+
−
    const_iterator begin() const noexcept;
+
−
    iterator      end() noexcept;
+
−
    const_iterator end() const noexcept;
+
−
    const_iterator cbegin() const noexcept;
+
−
    const_iterator cend() const noexcept;
+
−
 
+
−
    // capacity
+
−
    [[nodiscard]] bool empty() const noexcept;
+
−
    size_type size() const noexcept;
+
−
    size_type max_size() const noexcept;
+
−
 
+
−
    // modifiers
+
−
    template<class... Args> iterator emplace(Args&&... args);
+
−
    template<class... Args> iterator emplace_hint(const_iterator position,
+
−
                                                  Args&&... args);
+
−
    iterator insert(const value_type& obj);
+
−
    iterator insert(value_type&& obj);
+
−
    template<class P> iterator insert(P&& obj);
+
−
    iterator insert(const_iterator hint, const value_type& obj);
+
−
    iterator insert(const_iterator hint, value_type&& obj);
+
−
    template<class P> iterator insert(const_iterator hint, P&& obj);
+
−
    template<class InputIt> void insert(InputIt first, InputIt last);
+
−
    template<__container_compatible_range<value_type> R>
+
−
      void insert_range(R&& rg);
+
−
    void insert(initializer_list<value_type>);
+
−
 
+
−
    node_type extract(const_iterator position);
+
−
    node_type extract(const key_type& x);
+
−
    template<class K> node_type extract(K&& x);
+
−
    iterator insert(node_type&& nh);
+
−
    iterator insert(const_iterator hint, node_type&& nh);
+
−
 
+
−
    iterator  erase(iterator position);
+
−
    iterator  erase(const_iterator position);
+
−
    size_type erase(const key_type& k);
+
−
    template<class K> size_type erase(K&& x);
+
−
    iterator  erase(const_iterator first, const_iterator last);
+
−
    void      swap(unordered_multimap&)
+
−
      noexcept(allocator_traits<Allocator>::is_always_equal::value &&
+
−
              is_nothrow_swappable_v<Hash> &&
+
−
              is_nothrow_swappable_v<Pred>);
+
−
    void      clear() noexcept;
+
−
 
+
−
    template<class H2, class P2>
+
−
      void merge(unordered_multimap<Key, T, H2, P2, Allocator>& source);
+
−
    template<class H2, class P2>
+
−
      void merge(unordered_multimap<Key, T, H2, P2, Allocator>&& source);
+
−
    template<class H2, class P2>
+
−
      void merge(unordered_map<Key, T, H2, P2, Allocator>& source);
+
−
    template<class H2, class P2>
+
−
      void merge(unordered_map<Key, T, H2, P2, Allocator>&& source);
+
−
 
+
−
    // observers
+
−
    hasher hash_function() const;
+
−
    key_equal key_eq() const;
+
−
 
+
−
    // map operations
+
−
    iterator        find(const key_type& k);
+
−
    const_iterator  find(const key_type& k) const;
+
−
    template<class K>
+
−
      iterator      find(const K& k);
+
−
    template<class K>
+
−
      const_iterator find(const K& k) const;
+
−
    size_type        count(const key_type& k) const;
+
−
    template<class K>
+
−
      size_type      count(const K& k) const;
+
−
    bool            contains(const key_type& k) const;
+
−
    template<class K>
+
−
      bool          contains(const K& k) const;
+
−
    pair<iterator, iterator>              equal_range(const key_type& k);
+
−
    pair<const_iterator, const_iterator>  equal_range(const key_type& k) const;
+
−
    template<class K>
+
−
      pair<iterator, iterator>            equal_range(const K& k);
+
−
    template<class K>
+
−
      pair<const_iterator, const_iterator> equal_range(const K& k) const;
+
−
 
+
−
    // bucket interface
+
−
    size_type bucket_count() const noexcept;
+
−
    size_type max_bucket_count() const noexcept;
+
−
    size_type bucket_size(size_type n) const;
+
−
    size_type bucket(const key_type& k) const;
+
−
    local_iterator begin(size_type n);
+
−
    const_local_iterator begin(size_type n) const;
+
−
    local_iterator end(size_type n);
+
−
    const_local_iterator end(size_type n) const;
+
−
    const_local_iterator cbegin(size_type n) const;
+
−
    const_local_iterator cend(size_type n) const;
+
−
 
+
−
    // hash policy
+
−
    float load_factor() const noexcept;
+
−
    float max_load_factor() const noexcept;
+
−
    void max_load_factor(float z);
+
−
    void rehash(size_type n);
+
−
    void reserve(size_type n);
+
−
  };
+
−
 
+
−
  template<class InputIt,
+
−
          class Hash = hash<__iter_key_type<InputIt>>,
+
−
          class Pred = equal_to<__iter_key_type<InputIt>>,
+
−
          class Allocator = allocator<__iter_to_alloc_type<InputIt>>>
+
−
    unordered_multimap(InputIt, InputIt,
+
−
                      typename /* see description */::size_type = /* see description */,
+
−
                      Hash = Hash(), Pred = Pred(), Allocator = Allocator())
+
−
      -> unordered_multimap<__iter_key_type<InputIt>, __iter_mapped_type<InputIt>,
+
−
                            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 InputIt, class Allocator>
+
−
    unordered_multimap(InputIt, InputIt, typename /* see description */::size_type,
+
−
                      Allocator)
+
−
      -> unordered_multimap<__iter_key_type<InputIt>, __iter_mapped_type<InputIt>,
+
−
                            hash<__iter_key_type<InputIt>>,
+
−
                            equal_to<__iter_key_type<InputIt>>, Allocator>;
+
−
 
+
−
  template<class InputIt, class Allocator>
+
−
    unordered_multimap(InputIt, InputIt, Allocator)
+
−
      -> unordered_multimap<__iter_key_type<InputIt>, __iter_mapped_type<InputIt>,
+
−
                            hash<__iter_key_type<InputIt>>,
+
−
                            equal_to<__iter_key_type<InputIt>>, Allocator>;
+
−
 
+
−
  template<class InputIt, class Hash, class Allocator>
+
−
    unordered_multimap(InputIt, InputIt, typename /* see description */::size_type, Hash,
+
−
                      Allocator)
+
−
      -> unordered_multimap<__iter_key_type<InputIt>, __iter_mapped_type<InputIt>, Hash,
+
−
                            equal_to<__iter_key_type<InputIt>>, 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>;
+
−
}
+
−
}}
+
  
 
{{langlinks|de|es|ja|ru|zh}}
 
{{langlinks|de|es|ja|ru|zh}}

Latest revision as of 07:06, 27 November 2023

 
C++
 
Standard library headers
General utilities
<any> (C++17)
<bitset>
<bit> (C++20)
<charconv> (C++17)
<expected> (C++23)
<format> (C++20)
<functional>
<optional> (C++17)
<tuple> (C++11)
<typeindex> (C++11)
<utility>
<variant> (C++17)
Containers
<array> (C++11)
<deque>
<flat_map> (C++23)
<flat_set> (C++23)
<forward_list> (C++11)
<inplace_vector> (C++26)   
<list>
<map>
<mdspan> (C++23)
<queue>
<set>
<span> (C++20)
<stack>
<unordered_map> (C++11)
<unordered_set> (C++11)
<vector>
Iterators
<iterator>
Ranges
<generator> (C++23)
<ranges> (C++20)
 

This header is part of the containers library.

Contents

Includes

(C++20)
 Three-way comparison operator support[edit]
(C++11)
 std::initializer_list class template[edit]

Classes

(C++11)
 collection of key-value pairs, hashed by keys, keys are unique
(class template) [edit]
(C++11)
 collection of key-value pairs, hashed by keys
(class template) [edit]

Functions

(C++11)(C++11)(removed in C++20)
 compares the values in the unordered_map
(function template) [edit]
(C++11)
 specializes the std::swap algorithm
(function template) [edit]
(C++20)
 erases all elements satisfying specific criteria
(function template) [edit]
(C++11)(C++11)(removed in C++20)
 compares the values in the unordered_multimap
(function template) [edit]
(C++11)
 specializes the std::swap algorithm
(function template) [edit]
(C++20)
 erases all elements satisfying specific criteria
(function template) [edit]
Range access
(C++11)(C++14)
 returns an iterator to the beginning of a container or array
(function template) [edit]
(C++11)(C++14)
 returns an iterator to the end of a container or array
(function template) [edit]
(C++14)
 returns a reverse iterator to the beginning of a container or array
(function template) [edit]
(C++14)
 returns a reverse end iterator for a container or array
(function template) [edit]
(C++17)(C++20)
 returns the size of a container or array
(function template) [edit]
(C++17)
 checks whether the container is empty
(function template) [edit]
(C++17)
 obtains the pointer to the underlying array
(function template) [edit]

[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>
  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>
  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>
  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>
  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>
  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>
  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>>>;
 
  }
}

[edit] 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              = typename allocator_traits<Allocator>::pointer;
    using const_pointer        = typename 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
    unordered_map();
    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>
    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>
    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());
    unordered_map(const unordered_map&);
    unordered_map(unordered_map&&);
    explicit unordered_map(const Allocator&);
    unordered_map(const unordered_map&, const type_identity_t<Allocator>&);
    unordered_map(unordered_map&&, const type_identity_t<Allocator>&);
    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());
    unordered_map(size_type n, const allocator_type& a)
      : unordered_map(n, hasher(), key_equal(), a)
    {
    }
    unordered_map(size_type n, const hasher& hf, const allocator_type& a)
      : unordered_map(n, hf, key_equal(), a)
    {
    }
    template<class InputIter>
    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>
    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>
    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>
    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)
    {
    }
    unordered_map(initializer_list<value_type> il, size_type n, const allocator_type& a)
      : unordered_map(il, n, hasher(), key_equal(), a)
    {
    }
    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)
    {
    }
    ~unordered_map();
    unordered_map& operator=(const unordered_map&);
    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>);
    unordered_map& operator=(initializer_list<value_type>);
    allocator_type get_allocator() const noexcept;
 
    // iterators
    iterator begin() noexcept;
    const_iterator begin() const noexcept;
    iterator end() noexcept;
    const_iterator end() const noexcept;
    const_iterator cbegin() const noexcept;
    const_iterator cend() const noexcept;
 
    // capacity
    bool empty() const noexcept;
    size_type size() const noexcept;
    size_type max_size() const noexcept;
 
    // modifiers
    template<class... Args>
    pair<iterator, bool> emplace(Args&&... args);
    template<class... Args>
    iterator emplace_hint(const_iterator position, Args&&... args);
    pair<iterator, bool> insert(const value_type& obj);
    pair<iterator, bool> insert(value_type&& obj);
    template<class P>
    pair<iterator, bool> insert(P&& obj);
    iterator insert(const_iterator hint, const value_type& obj);
    iterator insert(const_iterator hint, value_type&& obj);
    template<class P>
    iterator insert(const_iterator hint, P&& obj);
    template<class InputIter>
    void insert(InputIter first, InputIter last);
    template<container-compatible-range<value_type> R>
    void insert_range(R&& rg);
    void insert(initializer_list<value_type>);
 
    node_type extract(const_iterator position);
    node_type extract(const key_type& x);
    template<class K>
    node_type extract(K&& x);
    insert_return_type insert(node_type&& nh);
    iterator insert(const_iterator hint, node_type&& nh);
 
    template<class... Args>
    pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
    template<class... Args>
    pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
    template<class K, class... Args>
    pair<iterator, bool> try_emplace(K&& k, Args&&... args);
    template<class... Args>
    iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);
    template<class... Args>
    iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
    template<class K, class... Args>
    iterator try_emplace(const_iterator hint, K&& k, Args&&... args);
    template<class M>
    pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
    template<class M>
    pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
    template<class K, class M>
    pair<iterator, bool> insert_or_assign(K&& k, M&& obj);
    template<class M>
    iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
    template<class M>
    iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
    template<class K, class M>
    iterator insert_or_assign(const_iterator hint, K&& k, M&& obj);
 
    iterator erase(iterator position);
    iterator erase(const_iterator position);
    size_type erase(const key_type& k);
    template<class K>
    size_type erase(K&& x);
    iterator erase(const_iterator first, const_iterator last);
    void swap(unordered_map&) noexcept(
      allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_swappable_v<Hash>&&
        is_nothrow_swappable_v<Pred>);
    void clear() noexcept;
 
    template<class H2, class P2>
    void merge(unordered_map<Key, T, H2, P2, Allocator>& source);
    template<class H2, class P2>
    void merge(unordered_map<Key, T, H2, P2, Allocator>&& source);
    template<class H2, class P2>
    void merge(unordered_multimap<Key, T, H2, P2, Allocator>& source);
    template<class H2, class P2>
    void merge(unordered_multimap<Key, T, H2, P2, Allocator>&& source);
 
    // observers
    hasher hash_function() const;
    key_equal key_eq() const;
 
    // map operations
    iterator find(const key_type& k);
    const_iterator find(const key_type& k) const;
    template<class K>
    iterator find(const K& k);
    template<class K>
    const_iterator find(const K& k) const;
    size_type count(const key_type& k) const;
    template<class K>
    size_type count(const K& k) const;
    bool contains(const key_type& k) const;
    template<class K>
    bool contains(const K& k) const;
    pair<iterator, iterator> equal_range(const key_type& k);
    pair<const_iterator, const_iterator> equal_range(const key_type& k) const;
    template<class K>
    pair<iterator, iterator> equal_range(const K& k);
    template<class K>
    pair<const_iterator, const_iterator> equal_range(const K& k) const;
 
    // element access
    mapped_type& operator[](const key_type& k);
    mapped_type& operator[](key_type&& k);
    template<class K>
    mapped_type& operator[](K&& k);
    mapped_type& at(const key_type& k);
    const mapped_type& at(const key_type& k) const;
    template<class K>
    mapped_type& at(const K& k);
    template<class K>
    const mapped_type& at(const K& k) const;
 
    // bucket interface
    size_type bucket_count() const noexcept;
    size_type max_bucket_count() const noexcept;
    size_type bucket_size(size_type n) const;
    size_type bucket(const key_type& k) const;
    template<class K>
    size_type bucket(const K& k) const;
    local_iterator begin(size_type n);
    const_local_iterator begin(size_type n) const;
    local_iterator end(size_type n);
    const_local_iterator end(size_type n) const;
    const_local_iterator cbegin(size_type n) const;
    const_local_iterator cend(size_type n) const;
 
    // hash policy
    float load_factor() const noexcept;
    float max_load_factor() const noexcept;
    void max_load_factor(float z);
    void rehash(size_type n);
    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>;
}

[edit] 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              = typename allocator_traits<Allocator>::pointer;
    using const_pointer        = typename 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
    unordered_multimap();
    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>
    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>
    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());
    unordered_multimap(const unordered_multimap&);
    unordered_multimap(unordered_multimap&&);
    explicit unordered_multimap(const Allocator&);
    unordered_multimap(const unordered_multimap&, const type_identity_t<Allocator>&);
    unordered_multimap(unordered_multimap&&, const type_identity_t<Allocator>&);
    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());
    unordered_multimap(size_type n, const allocator_type& a)
      : unordered_multimap(n, hasher(), key_equal(), a)
    {
    }
    unordered_multimap(size_type n, const hasher& hf, const allocator_type& a)
      : unordered_multimap(n, hf, key_equal(), a)
    {
    }
    template<class InputIter>
    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>
    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>
    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>
    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)
    {
    }
    unordered_multimap(initializer_list<value_type> il,
                       size_type n,
                       const allocator_type& a)
      : unordered_multimap(il, n, hasher(), key_equal(), a)
    {
    }
    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)
    {
    }
    ~unordered_multimap();
    unordered_multimap& operator=(const unordered_multimap&);
    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>);
    unordered_multimap& operator=(initializer_list<value_type>);
    allocator_type get_allocator() const noexcept;
 
    // iterators
    iterator begin() noexcept;
    const_iterator begin() const noexcept;
    iterator end() noexcept;
    const_iterator end() const noexcept;
    const_iterator cbegin() const noexcept;
    const_iterator cend() const noexcept;
 
    // capacity
    bool empty() const noexcept;
    size_type size() const noexcept;
    size_type max_size() const noexcept;
 
    // modifiers
    template<class... Args>
    iterator emplace(Args&&... args);
    template<class... Args>
    iterator emplace_hint(const_iterator position, Args&&... args);
    iterator insert(const value_type& obj);
    iterator insert(value_type&& obj);
    template<class P>
    iterator insert(P&& obj);
    iterator insert(const_iterator hint, const value_type& obj);
    iterator insert(const_iterator hint, value_type&& obj);
    template<class P>
    iterator insert(const_iterator hint, P&& obj);
    template<class InputIter>
    void insert(InputIter first, InputIter last);
    template<container-compatible-range<value_type> R>
    void insert_range(R&& rg);
    void insert(initializer_list<value_type>);
 
    node_type extract(const_iterator position);
    node_type extract(const key_type& x);
    template<class K>
    node_type extract(K&& x);
    iterator insert(node_type&& nh);
    iterator insert(const_iterator hint, node_type&& nh);
 
    iterator erase(iterator position);
    iterator erase(const_iterator position);
    size_type erase(const key_type& k);
    template<class K>
    size_type erase(K&& x);
    iterator erase(const_iterator first, const_iterator last);
    void swap(unordered_multimap&) noexcept(
      allocator_traits<Allocator>::is_always_equal::value&& is_nothrow_swappable_v<Hash>&&
        is_nothrow_swappable_v<Pred>);
    void clear() noexcept;
 
    template<class H2, class P2>
    void merge(unordered_multimap<Key, T, H2, P2, Allocator>& source);
    template<class H2, class P2>
    void merge(unordered_multimap<Key, T, H2, P2, Allocator>&& source);
    template<class H2, class P2>
    void merge(unordered_map<Key, T, H2, P2, Allocator>& source);
    template<class H2, class P2>
    void merge(unordered_map<Key, T, H2, P2, Allocator>&& source);
 
    // observers
    hasher hash_function() const;
    key_equal key_eq() const;
 
    // map operations
    iterator find(const key_type& k);
    const_iterator find(const key_type& k) const;
    template<class K>
    iterator find(const K& k);
    template<class K>
    const_iterator find(const K& k) const;
    size_type count(const key_type& k) const;
    template<class K>
    size_type count(const K& k) const;
    bool contains(const key_type& k) const;
    template<class K>
    bool contains(const K& k) const;
    pair<iterator, iterator> equal_range(const key_type& k);
    pair<const_iterator, const_iterator> equal_range(const key_type& k) const;
    template<class K>
    pair<iterator, iterator> equal_range(const K& k);
    template<class K>
    pair<const_iterator, const_iterator> equal_range(const K& k) const;
 
    // bucket interface
    size_type bucket_count() const noexcept;
    size_type max_bucket_count() const noexcept;
    size_type bucket_size(size_type n) const;
    size_type bucket(const key_type& k) const;
    template<class K>
    size_type bucket(const K& k) const;
    local_iterator begin(size_type n);
    const_local_iterator begin(size_type n) const;
    local_iterator end(size_type n);
    const_local_iterator end(size_type n) const;
    const_local_iterator cbegin(size_type n) const;
    const_local_iterator cend(size_type n) const;
 
    // hash policy
    float load_factor() const noexcept;
    float max_load_factor() const noexcept;
    void max_load_factor(float z);
    void rehash(size_type n);
    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>;
}
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