std::popcount

 

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Defined in header <bit>
template<class T> constexpr int popcount(T x) noexcept;		(since C++20)

Returns the number of 1 bits in the value of x.

This overload only participates in overload resolution if T is an unsigned integer type (that is, unsigned char, unsigned short, unsigned int, unsigned long, unsigned long long, or an extended unsigned integer type).

Parameters

x

-

values of unsigned integer type

Return value

The number of 1 bits in the value of x.

Example

Run this code

#include <bit>
#include <bitset>
#include <cstdint>
#include <initializer_list>
#include <iostream>
 
int main()
{
    for (std::uint8_t i : { 0, 0b11111111, 0b00011101 }) {
        std::cout << "popcount(0b" << std::bitset<8>(i) << ") = "
                  << std::popcount(i) << '\n';
    }
}

Output:

popcount(0b00000000) = 0
popcount(0b11111111) = 8
popcount(0b00011101) = 4

See also

countl_zero (C++20)	counts the number of consecutive 0 bits, starting from the most significant bit (function template)
countl_one (C++20)	counts the number of consecutive 1 bits, starting from the most significant bit (function template)
countr_zero (C++20)	counts the number of consecutive 0 bits, starting from the least significant bit (function template)
countr_one (C++20)	counts the number of consecutive 1 bits, starting from the least significant bit (function template)