std::unordered_set<Key,Hash,KeyEqual,Allocator>::find

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Containers library

array (C++11)

vector

deque

forward_list (C++11)

list

set

multiset

map

multimap

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

stack

queue

priority_queue

span (C++20)

 

std::unordered_set

Member functions

unordered_set::unordered_set

unordered_set::~unordered_set

unordered_set::operator=

unordered_set::get_allocator

Iterators

unordered_set::beginunordered_set::cbegin

unordered_set::endunordered_set::cend

Capacity

unordered_set::empty

unordered_set::size

unordered_set::max_size

Modifiers

unordered_set::clear

unordered_set::insert

unordered_set::emplace

unordered_set::emplace_hint

unordered_set::erase

unordered_set::swap

unordered_set::extract (C++17)

unordered_set::merge (C++17)

Lookup

unordered_set::count

unordered_set::find

unordered_set::contains (C++20)

unordered_set::equal_range

Bucket interface

unordered_set::begin(size_type)unordered_set::cbegin(size_type)

unordered_set::end(size_type)unordered_set::cend(size_type)

unordered_set::bucket_count

unordered_set::max_bucket_count

unordered_set::bucket_size

unordered_set::bucket

Hash policy

unordered_set::load_factor

unordered_set::max_load_factor

unordered_set::rehash

unordered_set::reserve

Observers

unordered_set::hash_function

unordered_set::key_eq

Deduction guides(C++17)

 

iterator find( const Key& key );	(1)
iterator find( const Key& key, size_t hash );	(1)	(since C++20)
const_iterator find( const Key& key ) const;	(2)
const_iterator find( const Key& key, size_t hash ) const;	(2)	(since C++20)
template< class K > iterator find( const K& x );	(3)	(since C++20)
template< class K > iterator find( const K& x, size_t hash );	(3)	(since C++20)
template< class K > const_iterator find( const K& x ) const;	(4)	(since C++20)
template< class K > const_iterator find( const K& x, size_t hash ) const;	(4)	(since C++20)

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 only participates in overload resolution if the qualified-id Hash::transparent_key_equal is valid and denotes a type. This assumes that such Hash is callable with both K and Key type, and that its key_equal is transparent, which, together, allows calling this function without constructing an instance of Key.

If present, the hash parameter may be used to pass a pre-computed hash value as an optimization. The behavior is undefined if invoking hash_function() on the key passed do not produce the same value as hash.

(since C++20)

Parameters

key	-	key value of the element to search for
x	-	a value of any type that can be transparently compared with a key
hash	-	the hash value of the 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

Constant on average, worst case linear in the size of the container.

Example

Run this code

#include <iostream>
#include <unordered_set>
 
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";
    }
 
 
}

Output:

Found 2

See also

count	returns the number of elements matching specific key (public member function)
equal_range	returns range of elements matching a specific key (public member function)