std::unordered_set<Key,Hash,KeyEqual,Allocator>::count

Since C++11
  1. Returns the number of elements with key that compares equal to the specified argument key, which is either 0 or 1 since this container does not allow duplicates.

# Declarations

size_type count( const Key& key ) const;

(since C++11)

template< class K >
size_type count( const K& x ) const;

(since C++20)

# Parameters

# 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

#include <algorithm>
#include <iostream>
#include <unordered_set>
 
int main()
{
    std::unordered_set set{2, 7, 1, 8, 2, 8, 1, 8, 2, 8};
 
    std::cout << "The set is: ";
    for (int e : set)
        std::cout << e << ' ';
 
    const auto [min, max] = std::ranges::minmax(set);
 
    std::cout << "\nNumbers from " << min << " to " << max << " that are in the set: ";
    for (int i{min}; i <= max; ++i)
        if (set.count(i) == 1)
            std::cout << i << ' ';
    std::cout << '\n';
}

# See also