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std::unordered_set<Key,Hash,KeyEqual,Allocator>::insert

From cppreference.com
 
C++
 
Containers library
 
std::unordered_set
Member types
Member functions
Non-member functions
(until C++20)
Deduction guides (C++17)
 
std::pair<iterator,bool> insert( const value_type& value );
 (1) (since C++11)
std::pair<iterator,bool> insert( value_type&& value );
 (2) (since C++11)
iterator insert( const_iterator hint, const value_type& value );
 (3) (since C++11)
iterator insert( const_iterator hint, value_type&& value );
 (4) (since C++11)
template< class InputIt >
void insert( InputIt first, InputIt last );
 (5) (since C++11)
void insert( std::initializer_list<value_type> ilist );
 (6) (since C++11)
insert_return_type insert( node_type&& nh );
 (7) (since C++17)
iterator insert( const_iterator hint, node_type&& nh );
 (8) (since C++17)
template< class K >
std::pair<iterator, bool> insert( K&& obj );
 (9) (since C++23)
template< class K >
iterator insert( const_iterator hint, K&& obj );
 (10) (since C++23)

Inserts element(s) into the container, if the container does not already contain an element with an equivalent key.

1,2) Inserts value.
3,4) Inserts value, using hint as a non-binding suggestion to where the search should start.
5) Inserts elements from range [first, last). If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844).
6) Inserts elements from initializer list ilist. If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844).
7) If nh is an empty node handle, does nothing. Otherwise, inserts the element owned by nh into the container , if the container doesn't already contain an element with a key equivalent to nh.key(). The behavior is undefined if nh is not empty and get_allocator() != nh.get_allocator().
8) If nh is an empty node handle, does nothing and returns the end iterator. Otherwise, inserts the element owned by nh into the container, if the container doesn't already contain an element with a key equivalent to nh.key(), and returns the iterator pointing to the element with key equivalent to nh.key()(regardless of whether the insert succeeded or failed). If the insertion succeeds, nh is moved from, otherwise it retains ownership of the element. hint is used as a non-binding suggestion to where the search should start. The behavior is undefined if nh is not empty and get_allocator() != nh.get_allocator().
9) If *this already contains an element which transparently compares equivalent to obj, does nothing. Otherwise, constructs an object u of value_type with std::forward<K>(obj) and then inserts u into *this. If equal_range(u) != hash_function()(obj) || contains(u) is true, the behavior is undefined. The value_type must be EmplaceConstructible into unordered_set from std::forward<K>(obj). This overload participates in overload resolution only if Hash and KeyEqual are both transparent. This assumes that such Hash is callable with both K and Key type, and that the KeyEqual is transparent, which, together, allows calling this function without constructing an instance of Key.
10) If *this already contains an element which transparently compares equivalent to obj, does nothing.

Otherwise, constructs an object u of value_type with std::forward<K>(obj) and then inserts u into *this. Template:hint is used as a non-binding suggestion to where the search should start. If equal_range(u) != hash_function()(obj) || contains(u) is true, the behavior is undefined. The value_type must be EmplaceConstructible into unordered_set from std::forward<K>(obj). This overload participates in overload resolution only if:

  • std::is_convertible_v<K&&, const_iterator> and std::is_convertible_v<K&&, iterator> are both false, and
  • Hash::is_transparent and KeyEqual::is_transparent are valid and each denotes a type. This assumes that such Hash is callable with both K and Key type, and that the KeyEqual is transparent,
which, together, allows calling this function without constructing an instance of Key.

If after the operation the new number of elements is greater than old max_load_factor() * bucket_count() a rehashing takes place.
If rehashing occurs (due to the insertion), all iterators are invalidated. Otherwise (no rehashing), iterators are not invalidated. If the insertion is successful, pointers and references to the element obtained while it is held in the node handle are invalidated, and pointers and references obtained to that element before it was extracted become valid.(since C++17)

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