std::map<Key,T,Compare,Allocator>::count
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std::map (C++17)
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map::count
(C++20)
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
size_type count( const Key& key ) const;
(1)
(constexpr since C++26)
template< class K >
size_type count( const K& x ) const;
(2)
(since C++14) size_type count( const K& x ) const;
(constexpr since C++26)
Returns the number of elements with key that compares equivalent to the specified argument.
1) Returns the number of elements with key key.This is either 1 or 0 since keys are always unique.
2) Returns the number of elements with key that compares equivalent to x.
This overload participates in overload resolution only if
Compare is transparent. It allows calling this function without constructing an instance of Key.[edit] Parameters
key
-
key value of the elements to count
x
-
alternative value to compare to the keys
[edit] Return value
Number of elements with key that compares equivalent to key or x.
[edit] Complexity
Logarithmic in the size of the container plus linear in the number of elements found.
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_generic_associative_lookup |
201304L |
(C++14) | Heterogeneous comparison lookup in associative containers; overload (2) |
[edit] Example
This section is incomplete
Reason: no example
Reason: no example