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std::unordered_map::count

From cppreference.com
 
 
 
 
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, which is either 1 or 0 since this container does not allow duplicates.
2) Returns the number of elements with key that compares equivalent to the specified argument 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.

Contents

[edit] Parameters

key - key value of the elements to count

[edit] Return value

Number of elements with key key, that is either 1 or 0.

[edit] Complexity

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

[edit] See also

finds element with specific key
(public member function) [edit]
returns range of elements matching a specific key
(public member function) [edit]