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

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< cpp‎ | container‎ | unordered set

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)

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