std::unordered_map<Key,T,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 ); |
(1) | (since C++17) |
template< class P > std::pair<iterator,bool> insert( P&& 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 ); |
(3) | (since C++17) |
template< class P > iterator insert( const_iterator hint, P&& 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
. The overload (2) is equivalent to emplace(std::forward<P>(value)) and only participates in overload resolution if std::is_constructible<value_type, P&&>::value == true.value
, using hint
as a non-binding suggestion to where the search should start. The overload (4) is equivalent to emplace_hint(hint, std::forward<P>(value)) and only participates in overload resolution if std::is_constructible<value_type, P&&>::value == true.[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).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)
Contents |
[edit] 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.
|
[edit] Return value
insert_return_type
with the members initialized as follows:
- If nh is empty,
inserted
is false,position
is end(), andnode
is empty. - Otherwise if the insertion took place,
inserted
is true,position
points to the inserted element, andnode
is empty. - If the insertion failed,
inserted
is false,node
has the previous value of nh, andposition
points to an element with a key equivalent to nh.key().
[edit] Exceptions
This section is incomplete Reason: cases 5-6 |
[edit] 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())
[edit] 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.
[edit] Example
#include <string> #include <iostream> #include <unordered_map> int main () { std::unordered_map<int, std::string> dict = {{1, "one"}, {2, "two"}}; dict.insert({3, "three"}); dict.insert(std::make_pair(4, "four")); dict.insert({{4, "another four"}, {5, "five"}}); bool ok = dict.insert({1, "another one"}).second; std::cout << "inserting 1 -> \"another one\" " << (ok ? "succeeded" : "failed") << '\n'; std::cout << "contents:\n"; for(auto& p: dict) std::cout << " " << p.first << " => " << p.second << '\n'; }
Possible output:
inserting 1 -> "another one" failed contents: 5 => five 1 => one 2 => two 3 => three 4 => four
[edit] See also
(C++11) |
constructs element in-place (public member function) |
(C++11) |
constructs elements in-place using a hint (public member function) |
(C++17) |
inserts an element or assigns to the current element if the key already exists (public member function) |
creates a std::insert_iterator of type inferred from the argument (function template) |