Standard library header <unordered_map>

 

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Standard Library header files

Language Support
<cstddef> <limits> <climits> <cfloat> <cstdint> <new> <typeinfo> <exception> <ciso646>	<initializer_list> <csignal> <csetjmp> <cstdalign> <cstdarg> <cstdbool> <cstdlib> <ctime>
Diagnostics
<stdexcept> <cassert>	<cerrno> <system_error>
General utilities
<utility> <tuple> <bitset> <memory> <cstdlib> <cstring> <functional>	<type_traits> <ratio> <chrono> <ctime> <scoped_allocator> <typeindex>
Strings
<string> <cctype> <cwctype> <cstring>	<cwchar> <cstdlib> <cuchar>
Localization
<locale> <codectv> <clocale>

Containers
<array> <deque> <forward_list> <list> <vector> <map>	<set> <unordered_map> <unordered_set> <queue> <stack>
Iterators
<iterator>
Algorithms
<algorithm>	<cstdlib>
Numerics
<cfenv> <complex> <random> <valarray>	<numeric> <cmath> <ctgmath> <cstdlib>
Input/Output
<iosfwd> <iostream> <ios> <streambuf> <istream> <ostream>	<iomanip> <sstream> <fstream> <cstdio> <cinttypes>
Regular expressions
<regex>
Thread support
<thread> <mutex> <atomic>	<condition_variable> <future>

 

This header is part of the containers library.

Includes
<initializer_list> (C++11)
Classes
unordered_map (since C++11)	collection of key-value pairs, hashed by keys, keys are unique (class template)
unordered_multimap (since C++11)	collection of key-value pairs, hashed by keys (class template)
Functions
operator== operator!=	compares the values in the unordered_map (function template)
std::swap(std::unordered_map)	specializes the std::swap algorithm (function template)
operator== operator!=	compares the values in the unordered_multimap (function template)
std::swap(std::unordered_multimap)	specializes the std::swap algorithm (function template)

Synopsis

#include <initializer_list>
 
namespace std {
 
    // class template unordered_map:
    template <class Key,
        class T,
        class Hash = hash<Key>,
        class Pred = std::equal_to<Key>,
        class Alloc = std::allocator<std::pair<const Key, T> > >
    class unordered_map;
 
    // 23.5.5, class template unordered_multimap:
    template <class Key,
        class T,
        class Hash = hash<Key>,
        class Pred = std::equal_to<Key>,
        class Alloc = std::allocator<std::pair<const Key, T> > >
    class unordered_multimap;
 
    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);
    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);
 
    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_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>
    bool operator!=(const unordered_multimap<Key, T, Hash, Pred, Alloc>& a,
                        const unordered_multimap<Key, T, Hash, Pred, Alloc>& b);
 
} // namespace std

Class std::unordered_map

template <class Key,
    class T,
    class Hash = hash<Key>,
    class Pred = std::equal_to<Key>,
    class Allocator = std::allocator<std::pair<const Key, T> > >
class unordered_map
{
public:
    // types
    typedef Key                                         key_type;
    typedef Key                                         value_type;
    typedef Hash                                        hasher;
    typedef Pred                                        key_equal;
    typedef Allocator                                   allocator_type;
    typedef typename allocator_type::pointer            pointer;
    typedef typename allocator_type::const_pointer      const_pointer;
    typedef typename allocator_type::reference          reference;
    typedef typename allocator_type::const_reference    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
    explicit unordered_map(size_type n = see below,
                           const hasher& hf = hasher(),
                           const key_equal& eql = key_equal(),
                           const allocator_type& a = allocator_type());
    template <class InputIterator>
    unordered_map(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_map(const unordered_map&);
    unordered_map(unordered_map&&);
    explicit unordered_map(const Allocator&);
    unordered_map(const unordered_map&, const Allocator&);
    unordered_map(unordered_map&&, const Allocator&);
    unordered_map(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_map();
    unordered_map& operator=(const unordered_map&);
    unordered_map& operator=(unordered_map&&);
    unordered_map& 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);
    template <class P> pair<iterator, bool> insert(P&& obj);
    iterator insert(const_iterator hint, const value_type& obj);
    template <class P> iterator insert(const_iterator hint, P&& 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_map&);
 
 
    // 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;
    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);
};

Class std::unordered_multimap

template <class Key,
class T,
class Hash = hash<Key>,
class Pred = std::equal_to<Key>,
class Allocator = std::allocator<std::pair<const Key, T> > >
class unordered_multimap
{
public:
    // types
    typedef Key                                         key_type;
    typedef Key                                         value_type;
    typedef Hash                                        hasher;
    typedef Pred                                        key_equal;
    typedef Allocator                                   allocator_type;
    typedef typename allocator_type::pointer            pointer;
    typedef typename allocator_type::const_pointer      const_pointer;
    typedef typename allocator_type::reference          reference;
    typedef typename allocator_type::const_reference    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
    explicit unordered_multimap(size_type n = see below,
                                const hasher& hf = hasher(),
                                const key_equal& eql = key_equal(),
                                const allocator_type& a = allocator_type());
    template <class InputIterator>
    unordered_multimap(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_multimap(const unordered_multimap&);
    unordered_multimap(unordered_multimap&&);
    explicit unordered_multimap(const Allocator&);
    unordered_multimap(const unordered_multimap&, const Allocator&);
    unordered_multimap(unordered_multimap&&, const Allocator&);
    unordered_multimap(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_multimap();
    unordered_multimap& operator=(const unordered_multimap&);
    unordered_multimap& operator=(unordered_multimap&&);
    unordered_multimap& 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> iterator emplace(Args&&... args);
    template <class... Args> iterator emplace_hint(const_iterator position, Args&&... args);
    iterator insert(const value_type& obj);
    template <class P> iterator insert(P&& obj);
    iterator insert(const_iterator hint, const value_type& obj);
    template <class P> iterator insert(const_iterator hint, P&& 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_multimap&);
 
 
 
    // 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);
};