# std::set<Key,Compare,Allocator>::find

From cppreference.com
< cpp‎ | container‎ | set

iterator find( const Key& key ); | (1) |
const_iterator find( const Key& key ) const; | (2) |
template< class K > iterator find( const K& x ); | (3) | (since C++14)
template< class K > const_iterator find( const K& x ) const; | (4) | (since C++14)

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 if the qualified-id Compare::is_transparent is valid and denotes a type. It allows calling this function without constructing an instance of `Key`.

### Parameters

key | - | key value of the element to search for
x | - | 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

Logarithmic in the size of the container.

### Notes

Feature-test macro | Value | Std | Comment
--- | --- | --- | ---
`__cpp_lib_generic_associative_lookup` | 201304L | (C++14) | Heterogeneous comparison lookup in associative containers; overloads (3,4)

### Example

Run this code

    #include <iostream>
    #include <set>

    struct FatKey   { int x; int data[1000]; };
    struct LightKey { int x; };
    // Note: as detailed above, the container must use std::less<> (or other
    //   transparent Comparator) to access these overloads.
    // This includes standard overloads, such as between std::string and std::string_view.
    bool operator<(const FatKey& fk, const LightKey& lk) { return fk.x < lk.x; }
    bool operator<(const LightKey& lk, const FatKey& fk) { return lk.x < fk.x; }
    bool operator<(const FatKey& fk1, const FatKey& fk2) { return fk1.x < fk2.x; }

    int main()
    {
        // simple comparison demo
        std::set<int> example = {1, 2, 3, 4};

        if (auto search = example.find(2); search != example.end())
            std::cout << "Found " << (*search) << '\n';
        else
            std::cout << "Not found\n";

        // transparent comparison demo
        std::set<FatKey, std::less<>> example2 = {{1, {}}, {2, {}}, {3, {}}, {4, {}}};

        LightKey lk = {2};
        if (auto search = example2.find(lk); search != example2.end())
            std::cout << "Found " << search->x << '\n';
        else
            std::cout << "Not found\n";

    }

Output:

    Found 2
    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)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/container/set/find&oldid=135455"