std::unordered_set insert() method
- since C++17
- until C++17
// (1) Non const version only
std::pair<iterator, bool> insert( const value_type& value );
// (2) Non const version only
std::pair<iterator, bool> insert( value_type&& value );
// (3) Non const version only
iterator insert( const_iterator hint, const value_type& value );
// (4) Non const version only
iterator insert( const_iterator hint, value_type&& value );
// (5) Non const version only
template< class InputIt >
void insert( InputIt first, InputIt last );
// (6) Non const version only
void insert( std::initializer_list<value_type> ilist );
// (7) Non const version only
insert_return_type insert( node_type&& nh );
// (8) Non const version only
iterator insert( const_iterator hint, node_type&& nh );
// (1) Non const version only
std::pair<iterator, bool> insert( const value_type& value );
// (2) Non const version only
std::pair<iterator, bool> insert( value_type&& value );
// (3) Non const version only
iterator insert( const_iterator hint, const value_type& value );
// (4) Non const version only
iterator insert( const_iterator hint, value_type&& value );
// (5) Non const version only
template< class InputIt >
void insert( InputIt first, InputIt last );
// (6) Non const version only
void insert( std::initializer_list<value_type> ilist );
Inserts element(s) into the container, if the container doesn't 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 tonh.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 tonh.key()
, and returns the iterator pointing to the element with key equivalent tonh.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 tohint
.
The behavior is undefined if nh
is not empty and get_allocator() != nh.get_allocator()
.
- since C++17
- until C++17
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.
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()
.
Parameters
hint
- iterator, used as a suggestion as to where to insert the contentvalue
- element value to insertfirst, last
- range of elements to insertilist
- initializer list to insert the values fromnh
- a compatible node handle
Type requirements
- (5) -
InputIt
must meet the requirements ofLegacyInputIterator
.
Return value
- (1-2) - Returns a pair consisting of an iterator to the inserted element (or to the element that prevented the insertion) and a
bool
denoting whether the insertion took place (true
if insertion happened,false
if it did not). - (3-4) - Returns an iterator to the inserted element, or to the element that prevented the insertion.
- (5-6) - (none)
- (7) - Returns an
insert_return_type
with the members initialized as follows:- If
nh
is empty,inserted
isfalse
,position
isend()
, andnode
isempty
. - Otherwise if the insertion took place,
inserted
istrue
,position
points to the inserted element, andnode
isempty
. - If the insertion failed,
inserted
isfalse
,node
has the previous value of nh, andposition
points to an element with a key equivalent tonh.key()
.
- If
- (8) - End iterator if
nh
was empty, iterator pointing to the inserted element if insertion took place, and iterator pointing to an element with a key equivalent tonh.key()
if it failed.
Complexity
-
(1-4)
Average case: O(1).
Worst case: O(size()). -
(5-6)
Average case: O(N) (where N is the number of elements to insert).
Worst case: O(N * size()+N). -
(7-8)
Average case: O(1).
Worst case: O(size()).
Exceptions
- (1-4) If an exception is thrown by any operation, the insertion has no effect.
This section requires improvement. You can help by editing this doc page.
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;
}::cout << " " << p.first << " => " << p.second << '\n';
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 }
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