# std::multimap<Key,T,Compare,Allocator>::find

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< cpp‎ | container‎ | multimap

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`. If there are several elements with `key` in the container, any of them may be returned.
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 <map>

    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::multimap<int,char> example = {{1,'a'}, {2,'b'}};

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

        // transparent comparison demo
        std::multimap<FatKey, char, std::less<>> example2 = {{{1, {}}, 'a'}, {{2, {}}, 'b'}};

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

        // Obtaining const iterators.
        // Compiler decides whether to return iterator of (non) const type by way of accessing
        // map; to prevent modification on purpose, one of easiest choices is to access map by
        // const reference.
        const auto& example2ref = example2;
        if (auto search = example2ref.find(lk); search != example2.end())
        {
            std::cout << "Found " << search->first.x << ' ' << search->second << '\n';
        //  search->second = 'c'; // error: assignment of member
                                  // 'std::pair<const FatKey, char>::second'
                                  // in read-only object
        }
    }

Output:

    Found 2 b
    Found 2 b
    Found 2 b

### 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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