# std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::count

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< cpp‎ | container‎ | unordered multimap

size_type count( const Key& key ) const; | (1) | (since C++11)
template< class K > size_type count( const K& x ) const; | (2) | (since C++20)

1) Returns the number of elements with key that compares equal to the specified argument key.
2) Returns the number of elements with key that compares equivalent to the specified argument x. This overload participates in overload resolution only if Hash::is_transparent and KeyEqual::is_transparent are valid and each denotes a type. This assumes that such `Hash` is callable with both `K` and `Key` type, and that the `KeyEqual` is transparent, which, together, allows calling this function without constructing an instance of `Key`.

### Parameters

key | - | key value of the elements to count
x | - | a value of any type that can be transparently compared with a key

### Return value

1) Number of elements with key key.
2) Number of elements with key that compares equivalent to x.

### Complexity

linear in the number of elements with key key on average, worst case linear in the size of the container.

### Notes

Feature-test macro | Value | Std | Feature
--- | --- | --- | ---
`__cpp_lib_generic_unordered_lookup` | `201811L` | (C++20) | Heterogeneous comparison lookup in unordered associative containers, overload (2)

### Example

Run this code

    #include <iostream>
    #include <string>
    #include <unordered_map>

    int main()
    {
        std::unordered_multimap<int, std::string> dict = {
            {1, "one"}, {6, "six"}, {3, "three"}
        };
        dict.insert({4, "four"});
        dict.insert({5, "five"});
        dict.insert({6, "six"});

        std::cout << "dict: { ";
        for (auto const& [key, value] : dict)
            std::cout << '[' << key << "]=" << value << ' ';
        std::cout << "}\n\n";

        for (int i{1}; i != 8; ++i)
            std::cout << "dict.count(" << i << ") = " << dict.count(i) << '\n';
    }

Possible output:

    dict: { [5]=five [4]=four [1]=one [6]=six [6]=six [3]=three }

    dict.count(1) = 1
    dict.count(2) = 0
    dict.count(3) = 1
    dict.count(4) = 1
    dict.count(5) = 1
    dict.count(6) = 2
    dict.count(7) = 0

### See also

find | finds element with specific key (public member function)
contains (C++20) | checks if the container contains element with specific key (public member function)
equal_range | returns range of elements matching a specific key (public member function)

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