NAME¶

std::countr_one - std::countr_one

Synopsis¶

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

Returns the number of consecutive 1 bits in the value of x, starting from the least
significant bit ("right").

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 consecutive 1 bits in the value of x, starting from the least
significant bit.

Notes¶

Feature-test macro: __cpp_lib_bitops

Example¶

// Run this code

#include <bit>
#include <bitset>
#include <cstdint>
#include <iostream>

int main()
{
for (const std::uint8_t i : { 0, 0b11111111, 0b11111110, 0b11100011 }) {
std::cout << "countr_one( " << std::bitset<8>(i) << " ) = "
<< std::countr_one(i) << '\n';
}
}

Output:¶

countr_one( 00000000 ) = 0
countr_one( 11111111 ) = 8
countr_one( 11111110 ) = 0
countr_one( 11100011 ) = 2

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)
popcount counts the number of 1 bits in an unsigned integer
(C++20) (function template)
has_single_bit checks if a number is an integral power of two
(C++20) (function template)
count returns the number of bits set to true
(public member function of std::bitset<N>)
all
any checks if all, any or none of the bits are set to true
none (public member function of std::bitset<N>)
(C++11)