std::bitset<N>:: count

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C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
std::bitset
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

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