std::unordered_set<Key,Hash,KeyEqual,Allocator>::insert
| 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 doesn't already contain an element with an equivalent key.
[first, last). If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844).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::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.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
Hashis callable with bothKandKeytype, and that theKeyEqualis transparent,
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)
Parameters
| hint | - | iterator, used as a suggestion as to where to insert the content |
| value | - | element value to insert |
| first, last | - | range of elements to insert |
| ilist | - | initializer list to insert the values from |
| nh | - | a compatible node handle |
| obj | - | a value of any type that can be transparently compared with a key |
| Type requirements | ||
-InputIt must meet the requirements of LegacyInputIterator.
| ||
Return value
insert_return_type with the members initialized as follows:
- If nh is empty,
insertedis false,positionis end(), andnodeis empty. - Otherwise if the insertion took place,
insertedis true,positionpoints to the inserted element, andnodeis empty. - If the insertion failed,
insertedis false,nodehas the previous value of nh, andpositionpoints to an element with a key equivalent to nh.key().
Exceptions
| This section is incomplete Reason: cases 5-10 |
Complexity
O(1), worst case O(size()).O(N), where N is the number of elements to insert. Worst case: O(N * size() + N).O(1), worst case O(size()).Notes
The hinted insert (3,4) does not return a boolean in order to be signature-compatible with positional insert on sequential containers, such as std::vector::insert. This makes it possible to create generic inserters such as std::inserter. One way to check success of a hinted insert is to compare size() before and after.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_associative_heterogeneous_insertion |
202311L |
(C++26) | Heterogeneous overloads for the remaining member functions in ordered and unordered associative containers. (9,10) |
Example
#include <array> #include <iostream> #include <unordered_set> std::ostream& operator<<(std::ostream& os, std::unordered_set<int> const& s) { for (os << '[' << s.size() << "] { "; int i : s) os << i << ' '; return os << "}\n"; } int main () { std::unordered_set<int> nums{2, 3, 4}; std::cout << "1) Initially: " << nums << std::boolalpha; auto p = nums.insert(1); // insert element, overload (1) std::cout << "2) '1' was inserted: " << p.second << '\n'; std::cout << "3) After insertion: " << nums; nums.insert(p.first, 0); // insert with hint, overload (3) std::cout << "4) After insertion: " << nums; std::array<int, 4> a = {10, 11, 12, 13}; nums.insert(a.begin(), a.end()); // insert range, overload (5) std::cout << "5) After insertion: " << nums; nums.insert({20, 21, 22, 23}); // insert initializer_list, (6) std::cout << "6) After insertion: " << nums; std::unordered_set<int> other_nums = {42, 43}; auto node = other_nums.extract(other_nums.find(42)); nums.insert(std::move(node)); // insert node, overload (7) std::cout << "7) After insertion: " << nums; node = other_nums.extract(other_nums.find(43)); nums.insert(nums.begin(), std::move(node)); // insert node with hint, (8) std::cout << "8) After insertion: " << nums; }
Possible output:
1) Initially: [3] { 4 3 2 }
2) '1' was inserted: true
3) After insertion: [4] { 1 2 3 4 }
4) After insertion: [5] { 0 1 2 3 4 }
5) After insertion: [9] { 13 12 11 10 4 3 2 1 0 }
6) After insertion: [13] { 23 22 13 12 11 10 21 4 20 3 2 1 0 }
7) After insertion: [14] { 42 23 22 13 12 11 10 21 4 20 3 2 1 0 }
8) After insertion: [15] { 43 42 23 22 13 12 11 10 21 4 20 3 2 1 0 }See also
| constructs element in-place (public member function) | |
| constructs elements in-place using a hint (public member function) | |
| creates a std::insert_iterator of type inferred from the argument (function template) |