NAME¶

std::countl_zero - std::countl_zero

Synopsis¶

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

Returns the number of consecutive 0 bits in the value of x, starting from the most
significant bit ("left").

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 0 bits in the value of x, starting from the most
significant bit.

Notes¶

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>

int main()
{
for (const std::uint8_t i : {0, 0b11111111, 0b11110000, 0b00011110})
std::cout << "countl_zero( " << std::bitset<8>(i) << " ) = "
<< std::countl_zero(i) << '\n';
}

Output:¶

countl_zero( 00000000 ) = 8
countl_zero( 11111111 ) = 0
countl_zero( 11110000 ) = 0
countl_zero( 00011110 ) = 3

See also¶

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