Standard library header <unordered_map>
This header is part of the containers library.
Includes |
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(C++20)
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Three-way comparison operator support |
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(C++11)
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std::initializer_list class template |
Classes |
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(C++11)
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collection of key-value pairs, hashed by keys, keys are unique (class template) |
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(C++11)
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collection of key-value pairs, hashed by keys (class template) |
Functions |
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(removed in C++20)
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compares the values in the unordered_map (function template) |
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(C++11)
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specializes the std::swap algorithm (function template) |
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(C++20)
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Erases all elements satisfying specific criteria (function template) |
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(removed in C++20)
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compares the values in the unordered_multimap (function template) |
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(C++11)
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specializes the std::swap algorithm (function template) |
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(C++20)
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Erases all elements satisfying specific criteria (function template) |
Range access |
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(C++11)(C++14)
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returns an iterator to the beginning of a container or array (function template) |
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(C++11)(C++14)
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returns an iterator to the end of a container or array (function template) |
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(C++14)
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returns a reverse iterator to the beginning of a container or array (function template) |
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(C++14)
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returns a reverse end iterator for a container or array (function template) |
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(C++17)(C++20)
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returns the size of a container or array (function template) |
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(C++17)
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checks whether the container is empty (function template) |
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(C++17)
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obtains the pointer to the underlying array (function template) |
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)));
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);
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>>>;
}
}
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 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());
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> 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) { }
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);
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<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*/<InputIte>,
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<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>;
// swap
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)));
}
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 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());
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> 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) { }
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);
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<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<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>;
// swap
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)));
}
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