std::unordered_set - Man Page

using insert_return_type
using node_type

typedef _Hashtable::key_type key_type
Public typedefs.
typedef _Hashtable::value_type value_type
Public typedefs.
typedef _Hashtable::hasher hasher
Public typedefs.
typedef _Hashtable::key_equal key_equal
Public typedefs.
typedef _Hashtable::allocator_type allocator_type
Public typedefs.

typedef _Hashtable::pointer pointer
Iterator-related typedefs.
typedef _Hashtable::const_pointer const_pointer
Iterator-related typedefs.
typedef _Hashtable::reference reference
Iterator-related typedefs.
typedef _Hashtable::const_reference const_reference
Iterator-related typedefs.
typedef _Hashtable::iterator iterator
Iterator-related typedefs.
typedef _Hashtable::const_iterator const_iterator
Iterator-related typedefs.
typedef _Hashtable::local_iterator local_iterator
Iterator-related typedefs.
typedef _Hashtable::const_local_iterator const_local_iterator
Iterator-related typedefs.
typedef _Hashtable::size_type size_type
Iterator-related typedefs.
typedef _Hashtable::difference_type difference_type
Iterator-related typedefs.

unordered_set ()=default
Default constructor.
template<typename _InputIterator > unordered_set (_InputIterator __first, _InputIterator __last, size_type __n, const allocator_type &__a)
template<typename _InputIterator > unordered_set (_InputIterator __first, _InputIterator __last, size_type __n, const hasher &__hf, const allocator_type &__a)
template<typename _InputIterator > unordered_set (_InputIterator __first, _InputIterator __last, size_type __n=0, const hasher &__hf=hasher(), const key_equal &__eql=key_equal(), const allocator_type &__a=allocator_type())
Builds an unordered_set from a range.
unordered_set (const allocator_type &__a)
Creates an unordered_set with no elements.
unordered_set (const unordered_set &)=default
Copy constructor.
unordered_set (const unordered_set &__uset, const allocator_type &__a)
unordered_set (initializer_list< value_type > __l, size_type __n, const allocator_type &__a)
unordered_set (initializer_list< value_type > __l, size_type __n, const hasher &__hf, const allocator_type &__a)
unordered_set (initializer_list< value_type > __l, size_type __n=0, const hasher &__hf=hasher(), const key_equal &__eql=key_equal(), const allocator_type &__a=allocator_type())
Builds an unordered_set from an initializer_list.
unordered_set (size_type __n, const allocator_type &__a)
unordered_set (size_type __n, const hasher &__hf, const allocator_type &__a)
unordered_set (size_type __n, const hasher &__hf=hasher(), const key_equal &__eql=key_equal(), const allocator_type &__a=allocator_type())
Default constructor creates no elements.
unordered_set (unordered_set &&)=default
Move constructor.
unordered_set (unordered_set &&__uset, const allocator_type &__a) noexcept(noexcept(_Hashtable(std::move(__uset._M_h), __a)))
size_type bucket (const key_type &__key) const
size_type bucket_count () const noexcept
Returns the number of buckets of the unordered_set.
size_type bucket_size (size_type __n) const
const_iterator cbegin () const noexcept
const_iterator cend () const noexcept
void clear () noexcept
template<typename... _Args> std::pair< iterator, bool > emplace (_Args &&... __args)
Attempts to build and insert an element into the unordered_set.
template<typename... _Args> iterator emplace_hint (const_iterator __pos, _Args &&... __args)
Attempts to insert an element into the unordered_set.
bool empty () const noexcept
Returns true if the unordered_set is empty.
size_type erase (const key_type &__x)
Erases elements according to the provided key.
iterator erase (const_iterator __first, const_iterator __last)
Erases a [__first,__last) range of elements from an unordered_set.
node_type extract (const key_type &__key)
Extract a node.
node_type extract (const_iterator __pos)
Extract a node.
allocator_type get_allocator () const noexcept
Returns the allocator object used by the unordered_set.
hasher hash_function () const
Returns the hash functor object with which the unordered_set was constructed.
template<typename _InputIterator > void insert (_InputIterator __first, _InputIterator __last)
A template function that attempts to insert a range of elements.
iterator insert (const_iterator, node_type &&__nh)
Re-insert an extracted node.
void insert (initializer_list< value_type > __l)
Attempts to insert a list of elements into the unordered_set.
insert_return_type insert (node_type &&__nh)
Re-insert an extracted node.
key_equal key_eq () const
Returns the key comparison object with which the unordered_set was constructed.
float load_factor () const noexcept
Returns the average number of elements per bucket.
size_type max_bucket_count () const noexcept
Returns the maximum number of buckets of the unordered_set.
float max_load_factor () const noexcept
Returns a positive number that the unordered_set tries to keep the load factor less than or equal to.
void max_load_factor (float __z)
Change the unordered_set maximum load factor.
size_type max_size () const noexcept
Returns the maximum size of the unordered_set.
template<typename _H2 , typename _P2 > void merge (unordered_multiset< _Value, _H2, _P2, _Alloc > &&__source)
template<typename _H2 , typename _P2 > void merge (unordered_multiset< _Value, _H2, _P2, _Alloc > &__source)
template<typename _H2 , typename _P2 > void merge (unordered_set< _Value, _H2, _P2, _Alloc > &&__source)
template<typename _H2 , typename _P2 > void merge (unordered_set< _Value, _H2, _P2, _Alloc > &__source)
unordered_set & operator= (const unordered_set &)=default
Copy assignment operator.
unordered_set & operator= (initializer_list< value_type > __l)
Unordered_set list assignment operator.
unordered_set & operator= (unordered_set &&)=default
Move assignment operator.
void rehash (size_type __n)
May rehash the unordered_set.
void reserve (size_type __n)
Prepare the unordered_set for a specified number of elements.
size_type size () const noexcept
Returns the size of the unordered_set.
void swap (unordered_set &__x) noexcept(noexcept(_M_h.swap(__x._M_h)))
Swaps data with another unordered_set.

iterator begin () noexcept
const_iterator begin () const noexcept

iterator end () noexcept
const_iterator end () const noexcept

std::pair< iterator, bool > insert (const value_type &__x)
Attempts to insert an element into the unordered_set.
std::pair< iterator, bool > insert (value_type &&__x)
Attempts to insert an element into the unordered_set.

iterator insert (const_iterator __hint, const value_type &__x)
Attempts to insert an element into the unordered_set.
iterator insert (const_iterator __hint, value_type &&__x)
Attempts to insert an element into the unordered_set.

iterator erase (const_iterator __position)
Erases an element from an unordered_set.
iterator erase (iterator __position)
Erases an element from an unordered_set.

iterator find (const key_type &__x)
Tries to locate an element in an unordered_set.
template<typename _Kt > auto find (const _Kt &__k) -> decltype(_M_h._M_find_tr(__k))
Tries to locate an element in an unordered_set.
const_iterator find (const key_type &__x) const
Tries to locate an element in an unordered_set.
template<typename _Kt > auto find (const _Kt &__k) const -> decltype(_M_h._M_find_tr(__k))
Tries to locate an element in an unordered_set.

size_type count (const key_type &__x) const
Finds the number of elements.
template<typename _Kt > auto count (const _Kt &__k) const -> decltype(_M_h._M_count_tr(__k))
Finds the number of elements.

bool contains (const key_type &__x) const
Finds whether an element with the given key exists.
template<typename _Kt > auto contains (const _Kt &__k) const -> decltype(_M_h._M_find_tr(__k), void(), true)
Finds whether an element with the given key exists.

std::pair< iterator, iterator > equal_range (const key_type &__x)
Finds a subsequence matching given key.
template<typename _Kt > auto equal_range (const _Kt &__k) -> decltype(_M_h._M_equal_range_tr(__k))
Finds a subsequence matching given key.
std::pair< const_iterator, const_iterator > equal_range (const key_type &__x) const
Finds a subsequence matching given key.
template<typename _Kt > auto equal_range (const _Kt &__k) const -> decltype(_M_h._M_equal_range_tr(__k))
Finds a subsequence matching given key.

local_iterator begin (size_type __n)
Returns a read-only (constant) iterator pointing to the first bucket element.
const_local_iterator begin (size_type __n) const
Returns a read-only (constant) iterator pointing to the first bucket element.
const_local_iterator cbegin (size_type __n) const
Returns a read-only (constant) iterator pointing to the first bucket element.

local_iterator end (size_type __n)
Returns a read-only (constant) iterator pointing to one past the last bucket elements.
const_local_iterator end (size_type __n) const
Returns a read-only (constant) iterator pointing to one past the last bucket elements.
const_local_iterator cend (size_type __n) const
Returns a read-only (constant) iterator pointing to one past the last bucket elements.

template<typename _Value1 , typename _Hash1 , typename _Pred1 , typename _Alloc1 > bool operator== (const unordered_set< _Value1, _Hash1, _Pred1, _Alloc1 > &, const unordered_set< _Value1, _Hash1, _Pred1, _Alloc1 > &)
template<typename , typename , typename > class std::_Hash_merge_helper

class std::unordered_set< _Value, _Hash, _Pred, _Alloc >"A standard container composed of unique keys (containing at most one of each key value) in which the elements' keys are the elements themselves.

Since

C++11

Template Parameters

Meets the requirements of a container, and unordered associative container

Base is _Hashtable, dispatched at compile time via template alias __uset_hashtable.

Public typedefs.

Iterator-related typedefs.

Iterator-related typedefs.

Iterator-related typedefs.

Iterator-related typedefs.

Iterator-related typedefs.

Public typedefs.

Iterator-related typedefs.

Public typedefs.

Public typedefs.

Iterator-related typedefs.

Iterator-related typedefs.

Iterator-related typedefs.

Iterator-related typedefs.

Public typedefs.

Default constructor.

Default constructor creates no elements.

Parameters

Builds an unordered_set from a range.

Parameters

Create an unordered_set consisting of copies of the elements from [__first,__last). This is linear in N (where N is distance(__first,__last)).

Copy constructor.

Move constructor.

Creates an unordered_set with no elements.

Parameters

Builds an unordered_set from an initializer_list.

Parameters

Create an unordered_set consisting of copies of the elements in the list. This is linear in N (where N is __l.size()).

Returns a read-only (constant) iterator that points to the first element in the unordered_set.

Returns a read-only (constant) iterator that points to the first element in the unordered_set.

Returns a read-only (constant) iterator pointing to the first bucket element.

Parameters

Returns

A read-only local iterator.

Returns a read-only (constant) iterator pointing to the first bucket element.

Parameters

Returns

A read-only local iterator.

Returns the number of buckets of the unordered_set.

Returns a read-only (constant) iterator that points to the first element in the unordered_set.

Returns a read-only (constant) iterator pointing to the first bucket element.

Parameters

Returns

A read-only local iterator.

Returns a read-only (constant) iterator that points one past the last element in the unordered_set.

Returns a read-only (constant) iterator pointing to one past the last bucket elements.

Parameters

Returns

A read-only local iterator.

Erases all elements in an unordered_set. Note that this function only erases the elements, and that if the elements themselves are pointers, the pointed-to memory is not touched in any way. Managing the pointer is the user's responsibility.

[inline]"

Finds whether an element with the given key exists.

Parameters

Returns

True if there is any element with the specified key.

Finds whether an element with the given key exists.

Parameters

Returns

True if there is any element with the specified key.

[inline]"

Finds the number of elements.

Parameters

Returns

Number of elements with specified key.

This function only makes sense for unordered_multisets; for unordered_set the result will either be 0 (not present) or 1 (present).

Finds the number of elements.

Parameters

Returns

Number of elements with specified key.

This function only makes sense for unordered_multisets; for unordered_set the result will either be 0 (not present) or 1 (present).

Attempts to build and insert an element into the unordered_set.

Parameters

Returns

A pair, of which the first element is an iterator that points to the possibly inserted element, and the second is a bool that is true if the element was actually inserted.

This function attempts to build and insert an element into the unordered_set. An unordered_set relies on unique keys and thus an element is only inserted if it is not already present in the unordered_set.

Insertion requires amortized constant time.

References std::forward().

Attempts to insert an element into the unordered_set.

Parameters

Returns

An iterator that points to the element with key equivalent to the one generated from __args (may or may not be the element itself).

This function is not concerned about whether the insertion took place, and thus does not return a boolean like the single-argument emplace() does. Note that the first parameter is only a hint and can potentially improve the performance of the insertion process. A bad hint would cause no gains in efficiency.

For more on hinting, see: https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

Insertion requires amortized constant time.

References std::forward().

Returns true if the unordered_set is empty.

Returns a read-only (constant) iterator that points one past the last element in the unordered_set.

Returns a read-only (constant) iterator that points one past the last element in the unordered_set.

Referenced by std::unordered_set< _Value, _Hash, _Pred, _Alloc >::extract().

Returns a read-only (constant) iterator pointing to one past the last bucket elements.

Parameters

Returns

A read-only local iterator.

Returns a read-only (constant) iterator pointing to one past the last bucket elements.

Parameters

Returns

A read-only local iterator.

[inline]"

Finds a subsequence matching given key.

Parameters

Returns

Pair of iterators that possibly points to the subsequence matching given key.

This function probably only makes sense for multisets.

[inline]"

Finds a subsequence matching given key.

Parameters

Returns

Pair of iterators that possibly points to the subsequence matching given key.

This function probably only makes sense for multisets.

Finds a subsequence matching given key.

Parameters

Returns

Pair of iterators that possibly points to the subsequence matching given key.

This function probably only makes sense for multisets.

Finds a subsequence matching given key.

Parameters

Returns

Pair of iterators that possibly points to the subsequence matching given key.

This function probably only makes sense for multisets.

Erases elements according to the provided key.

Parameters

Returns

The number of elements erased.

This function erases all the elements located by the given key from an unordered_set. For an unordered_set the result of this function can only be 0 (not present) or 1 (present). Note that this function only erases the element, and that if the element is itself a pointer, the pointed-to memory is not touched in any way. Managing the pointer is the user's responsibility.

Erases a [__first,__last) range of elements from an unordered_set.

Parameters

Returns

The iterator __last.

This function erases a sequence of elements from an unordered_set. Note that this function only erases the element, and that if the element is itself a pointer, the pointed-to memory is not touched in any way. Managing the pointer is the user's responsibility.

Erases an element from an unordered_set.

Parameters

Returns

An iterator pointing to the element immediately following __position prior to the element being erased. If no such element exists, end() is returned.

This function erases an element, pointed to by the given iterator, from an unordered_set. Note that this function only erases the element, and that if the element is itself a pointer, the pointed-to memory is not touched in any way. Managing the pointer is the user's responsibility.

Erases an element from an unordered_set.

Parameters

Returns

An iterator pointing to the element immediately following __position prior to the element being erased. If no such element exists, end() is returned.

This function erases an element, pointed to by the given iterator, from an unordered_set. Note that this function only erases the element, and that if the element is itself a pointer, the pointed-to memory is not touched in any way. Managing the pointer is the user's responsibility.

Extract a node.

Extract a node.

References std::unordered_set< _Value, _Hash, _Pred, _Alloc >::end().

[inline]"

Tries to locate an element in an unordered_set.

Parameters

Returns

Iterator pointing to sought-after element, or end() if not found.

This function takes a key and tries to locate the element with which the key matches. If successful the function returns an iterator pointing to the sought after element. If unsuccessful it returns the past-the-end ( end() ) iterator.

[inline]"

Tries to locate an element in an unordered_set.

Parameters

Returns

Iterator pointing to sought-after element, or end() if not found.

This function takes a key and tries to locate the element with which the key matches. If successful the function returns an iterator pointing to the sought after element. If unsuccessful it returns the past-the-end ( end() ) iterator.

Tries to locate an element in an unordered_set.

Parameters

Returns

Iterator pointing to sought-after element, or end() if not found.

This function takes a key and tries to locate the element with which the key matches. If successful the function returns an iterator pointing to the sought after element. If unsuccessful it returns the past-the-end ( end() ) iterator.

Tries to locate an element in an unordered_set.

Parameters

Returns

Iterator pointing to sought-after element, or end() if not found.

This function takes a key and tries to locate the element with which the key matches. If successful the function returns an iterator pointing to the sought after element. If unsuccessful it returns the past-the-end ( end() ) iterator.

Returns the allocator object used by the unordered_set.

Returns the hash functor object with which the unordered_set was constructed.

A template function that attempts to insert a range of elements.

Parameters

Complexity similar to that of the range constructor.

Attempts to insert an element into the unordered_set.

Parameters

Returns

A pair, of which the first element is an iterator that points to the possibly inserted element, and the second is a bool that is true if the element was actually inserted.

This function attempts to insert an element into the unordered_set. An unordered_set relies on unique keys and thus an element is only inserted if it is not already present in the unordered_set.

Insertion requires amortized constant time.

Attempts to insert an element into the unordered_set.

Parameters

Returns

An iterator that points to the element with key of __x (may or may not be the element passed in).

This function is not concerned about whether the insertion took place, and thus does not return a boolean like the single-argument insert() does. Note that the first parameter is only a hint and can potentially improve the performance of the insertion process. A bad hint would cause no gains in efficiency.

For more on hinting, see: https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

Insertion requires amortized constant.

Attempts to insert an element into the unordered_set.

Parameters

Returns

An iterator that points to the element with key of __x (may or may not be the element passed in).

This function is not concerned about whether the insertion took place, and thus does not return a boolean like the single-argument insert() does. Note that the first parameter is only a hint and can potentially improve the performance of the insertion process. A bad hint would cause no gains in efficiency.

For more on hinting, see: https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

Insertion requires amortized constant.

References std::move().

Re-insert an extracted node.

References std::move().

Attempts to insert a list of elements into the unordered_set.

Parameters

Complexity similar to that of the range constructor.

Re-insert an extracted node.

References std::move().

Attempts to insert an element into the unordered_set.

Parameters

Returns

A pair, of which the first element is an iterator that points to the possibly inserted element, and the second is a bool that is true if the element was actually inserted.

This function attempts to insert an element into the unordered_set. An unordered_set relies on unique keys and thus an element is only inserted if it is not already present in the unordered_set.

Insertion requires amortized constant time.

References std::move().

Returns the key comparison object with which the unordered_set was constructed.

Returns the average number of elements per bucket.

Returns the maximum number of buckets of the unordered_set.

Returns a positive number that the unordered_set tries to keep the load factor less than or equal to.

Change the unordered_set maximum load factor.

Parameters

Returns the maximum size of the unordered_set.

Copy assignment operator.

Unordered_set list assignment operator.

Parameters

This function fills an unordered_set with copies of the elements in the initializer list __l.

Note that the assignment completely changes the unordered_set and that the resulting unordered_set's size is the same as the number of elements assigned.

Move assignment operator.

May rehash the unordered_set.

Parameters

Rehash will occur only if the new number of buckets respect the unordered_set maximum load factor.

Prepare the unordered_set for a specified number of elements.

Parameters

Same as rehash(ceil(n / max_load_factor())).

Returns the size of the unordered_set.

Swaps data with another unordered_set.

Parameters

This exchanges the elements between two sets in constant time. Note that the global std::swap() function is specialized such that std::swap(s1,s2) will feed to this function.