std::bitset<N>::count

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

#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
(public member function)

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