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) |
Inserts element(s) into the container, if the container doesn't already contain an element with an equivalent key.
value
.
value
, using
hint
as a non-binding suggestion to where the search should start.
[first, last)
. If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending
LWG2844).
ilist
. If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending
LWG2844).
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()
.
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. The element is inserted as close as possible to
hint
. The behavior is undefined if
nh
is not empty and
get_allocator() != nh.get_allocator()
.
If rehashing occurs due to the insertion, all iterators are invalidated. Otherwise iterators are not affected. References are not invalidated. Rehashing occurs only if the new number of elements is greater than max_load_factor()*bucket_count()
. 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 |
Type requirements | ||
-InputIt must meet the requirements of LegacyInputIterator. |
Return value
bool
denoting whether the insertion took place.
insert_return_type
with the members initialized as follows:
- If
nh
is empty,inserted
isfalse
,position
isend()
, andnode
is empty. - Otherwise if the insertion took place,
inserted
istrue
,position
points to the inserted element, andnode
is empty. - If the insertion failed,
inserted
isfalse
,node
has the previous value ofnh
, andposition
points to an element with a key equivalent tonh.key()
.
nh
was empty, iterator pointing to the inserted element if insertion took place, and iterator pointing to an element with a key equivalent to
nh.key()
if it failed.
Exceptions
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.
Example
#include <unordered_set> #include <iostream> #include <array> 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 << "Initially: " << nums; auto p = nums.insert (1); // insert element std::cout << "'1' was inserted: " << std::boolalpha << p.second << '\n'; std::cout << "After insertion: " << nums; nums.insert (p.first, 0); // insert with hint std::cout << "After insertion: " << nums; std::array<int, 4> a = {10, 11, 12, 13}; nums.insert (a.begin (), a.end ()); // insert range std::cout << "After insertion: " << nums; nums.insert ({20, 21, 22, 23}); // insert initializer_list std::cout << "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 std::cout << "After insertion: " << nums; node = other_nums.extract (other_nums.find (43)); nums.insert (nums.begin (), std::move (node)); // insert node with hint std::cout << "After insertion: " << nums; }
Possible output:
Initially: [3] { 4 3 2 } '1' was inserted: true After insertion: [4] { 1 2 3 4 } After insertion: [5] { 0 1 2 3 4 } After insertion: [9] { 13 12 11 10 4 3 2 1 0 } After insertion: [13] { 23 22 13 12 11 10 21 4 20 3 2 1 0 } After insertion: [14] { 42 23 22 13 12 11 10 21 4 20 3 2 1 0 } After insertion: [15] { 43 42 23 22 13 12 11 10 21 4 20 3 2 1 0 }
See also
(C++11)
|
constructs element in-place (public member function) |
(C++11)
|
constructs elements in-place using a hint (public member function) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/container/unordered_set/insert