std::popcount

 

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popcount (C++20)

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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 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

The name popcount is a contraction for "population count".

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

Example

Run this code

#include <bit>
#include <bitset>
#include <cstdint>
#include <iostream>
 
static_assert(std::popcount(0xFULL) == 4);
 
int main()
{
    for (const std::uint8_t x : {0, 0b00011101, 0b11111111})
        std::cout << "popcount( " << std::bitset<8>(x) << " ) = "
                  << std::popcount(x) << '\n';
}

Output:

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

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)
has_single_bit (C++20)	checks if a number is an integral power of 2 (function template)
count	returns the number of bits set to true (public member function of std::bitset<N>)
allanynone	checks if all, any or none of the bits are set to true (public member function of std::bitset<N>)