NAME

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

Synopsis

std::size_t count() const; (until C++11)
std::size_t count() const noexcept; (since C++11)
(until C++23)
constexpr std::size_t count() const noexcept; (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 <iostream>
#include <bitset>

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)