NAME¶

std::bitset::count - std::bitset::count

Synopsis¶

std::size_t count() const; (noexcept since C++11)
(constexpr since C++23)

Returns the number of bits that are set to true.

Parameters¶

(none)

Return value¶

Number of bits that are set to true.

Example¶

// Run this code

#include <bitset>
#include <iostream>

int main()
{
std::bitset<8> b("00010010");
std::cout << "Initial value: " << b << '\n';

// Find the first unset bit
std::size_t idx = 0;
while (idx < b.size() && b.test(idx))
++idx;

// Continue setting bits until half the bitset is filled
while (idx < b.size() && b.count() < b.size() / 2)
{
b.set(idx);
std::cout << "Setting bit " << idx << ": " << b << '\n';
while (idx < b.size() && b.test(idx))
++idx;
}

}

Output:¶

Initial value: 00010010
Setting bit 0: 00010011
Setting bit 2: 00010111

See also¶

size returns the number of bits that the bitset holds
(public member function)
popcount counts the number of 1 bits in an unsigned integer
(C++20) (function template)