std::popcount

From cppreference.com
< cpp‎ | numeric
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 participates in overload resolution only 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 - value of unsigned integer type

Return value

The number of 1 bits in the value of x.

Notes

Feature-test macro Value Std Comment
__cpp_lib_bitops 201907L (C++20) Bit operations

Example

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

Output:

popcount( 00000000 ) = 0
popcount( 11111111 ) = 8
popcount( 00011101 ) = 4

See also

counts the number of consecutive 0 bits, starting from the most significant bit
(function template)
counts the number of consecutive 1 bits, starting from the most significant bit
(function template)
counts the number of consecutive 0 bits, starting from the least significant bit
(function template)
counts the number of consecutive 1 bits, starting from the least significant bit
(function template)
checks if a number is an integral power of two
(function template)
returns the number of bits set to true
(public member function of std::bitset<N>)
checks if all, any or none of the bits are set to true
(public member function of std::bitset<N>)