std::bitset::count (3) Linux Manual Page

std::bitset<N>::count – std::bitset<N>::count

Synopsis

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

     returns the size number of bits that the bitset can hold
size (public member function)