std::unordered_set find() method
- since C++20
- since C++11
// (1) Non const version
iterator find( const Key& key );
// (2) Const version
const_iterator find( const Key& key ) const;
// (3) Non const version
template< class K >
iterator find( const K& x );
// (4) Const version
template< class K >
const_iterator find( const K& x ) const;
// (1) Non const version
iterator find( const Key& key );
// (2) Const version
const_iterator find( const Key& key ) const;
- (1-2) Finds an element with key equivalent to
key
. - (3-4) Finds an element with key that compares equivalent to the value
x
. This overload participates in overload resolution only ifHash::is_transparent
andKeyEqual::is_transparent
are valid and each denotes a type. This assumes that suchHash
is callable with bothK
andKey
type, and that theKeyEqual
is transparent, which, together, allows calling this function without constructing an instance ofKey
.
Parameters
key
- key value of the elements to countx
- a value of any type that can be transparently compared with a key
Return value
Iterator to an element with key equivalent to key
. If no such element is found, past-the-end (see end()
) iterator is returned.
Complexity
Average case, constant - O(1).
Worst case, linear in the size of the container - O(size()).
Exceptions
(none)
Notes
Feature testing macro: __cpp_lib_generic_unordered_lookup
(for overload (3-4)).
Example
Main.cpp
#include <unordered_set>
#include <iostream>
int main()
{
// simple comparison demo
std::unordered_set<int> example = {1, 2, 3, 4};
auto search = example.find(2);
if (search != example.end()) {
std::cout << "Found " << (*search) << '\n';
} else {
std::cout << "Not found\n";
}
}
Possible output
Found 2 b
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