23 Containers library [containers]

An unordered_set is an unordered associative container that supports unique keys (an unordered_set contains at most one of each key value) and in which the elements' keys are the elements themselves. The unordered_set class supports forward iterators.

An unordered_set satisfies all of the requirements of a container, of an unordered associative container, and of an allocator-aware container (Table [tab:containers.allocatoraware]). It provides the operations described in the preceding requirements table for unique keys; that is, an unordered_set supports the a_uniq operations in that table, not the a_eq operations. For an unordered_set<Key> the key type and the value type are both Key. The iterator and const_iterator types are both const iterator types. It is unspecified whether they are the same type.

This section only describes operations on unordered_set that are not described in one of the requirement tables, or for which there is additional semantic information.

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

    typedef implementation-defined                              iterator;
    typedef implementation-defined                              const_iterator;
    typedef implementation-defined                              local_iterator;
    typedef implementation-defined                              const_local_iterator;

    // construct/destroy/copy
    unordered_set();
    explicit unordered_set(size_type n,
                           const hasher& hf = hasher(),
                           const key_equal& eql = key_equal(),
                           const allocator_type& a = allocator_type());
    template <class InputIterator>
      unordered_set(InputIterator f, InputIterator l,
                    size_type n = see below,
                    const hasher& hf = hasher(),
                    const key_equal& eql = key_equal(),
                    const allocator_type& a = allocator_type());
    unordered_set(const unordered_set&);
    unordered_set(unordered_set&&);
    explicit unordered_set(const Allocator&);
    unordered_set(const unordered_set&, const Allocator&);
    unordered_set(unordered_set&&, const Allocator&);
    unordered_set(initializer_list<value_type>,
      size_type = see below,
      const hasher& hf = hasher(),
      const key_equal& eql = key_equal(),
      const allocator_type& a = allocator_type());
    unordered_set(size_type n, const allocator_type& a)
      : unordered_set(n, hasher(), key_equal(), a) { }
    unordered_set(size_type n, const hasher& hf, const allocator_type& a)
      : unordered_set(n, hf, key_equal(), a) { }
    template <class InputIterator>
      unordered_set(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
      : unordered_set(f, l, n, hasher(), key_equal(), a) { }
    template <class InputIterator>
      unordered_set(InputIterator f, InputIterator l, size_type n, const hasher& hf,
      const allocator_type& a)
      : unordered_set(f, l, n, hf, key_equal(), a) { }
    unordered_set(initializer_list<value_type> il, size_type n, const allocator_type& a)
      : unordered_set(il, n, hasher(), key_equal(), a) { }
    unordered_set(initializer_list<value_type> il, size_type n, const hasher& hf,
    const allocator_type& a)
      : unordered_set(il, n, hf, key_equal(), a) { }
    ~unordered_set();
    unordered_set& operator=(const unordered_set&);
    unordered_set& operator=(unordered_set&&);
    unordered_set& operator=(initializer_list<value_type>);
    allocator_type get_allocator() const noexcept;

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

    // 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);
    iterator insert(const_iterator hint, const value_type& obj);
    iterator insert(const_iterator hint, value_type&& obj);
    template <class InputIterator> void insert(InputIterator first, InputIterator last);
    void insert(initializer_list<value_type>);

    iterator erase(const_iterator position);
    size_type erase(const key_type& k);
    iterator erase(const_iterator first, const_iterator last);
    void clear() noexcept;

    void swap(unordered_set&);

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

    // lookup
    iterator       find(const key_type& k);
    const_iterator find(const key_type& k) const;
    size_type count(const key_type& k) const;
    std::pair<iterator, iterator>             equal_range(const key_type& k);
    std::pair<const_iterator, const_iterator> equal_range(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 Key, class Hash, class Pred, class Alloc>
    void swap(unordered_set<Key, Hash, Pred, Alloc>& x,
              unordered_set<Key, Hash, Pred, Alloc>& y);

  template <class Key, class Hash, class Pred, class Alloc>
    bool operator==(const unordered_set<Key, Hash, Pred, Alloc>& a,
                    const unordered_set<Key, Hash, Pred, Alloc>& b);
  template <class Key, class Hash, class Pred, class Alloc>
    bool operator!=(const unordered_set<Key, Hash, Pred, Alloc>& a,
                    const unordered_set<Key, Hash, Pred, Alloc>& b);
}