NAME¶

std::popcount - std::popcount

Synopsis¶

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

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 counts the number of consecutive 0 bits, starting from the most
(C++20) significant bit
(function template)
countl_one counts the number of consecutive 1 bits, starting from the most
(C++20) significant bit
(function template)
countr_zero counts the number of consecutive 0 bits, starting from the least
(C++20) significant bit
(function template)
countr_one counts the number of consecutive 1 bits, starting from the least
(C++20) significant bit
(function template)
has_single_bit checks if a number is an integral power of 2
(C++20) (function template)
count returns the number of bits set to true
(public member function of std::bitset<N>)
all checks if all, any or none of the bits are set to true
any (public member function of std::bitset<N>)
none