std::bitset<N>::count

 

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std::bitset

Member types
bitset::reference
Member functions
bitset::bitset
bitset::operator==bitset::operator!= (until C++20)
Element access
bitset::operator[]
bitset::test
bitset::allbitset::anybitset::none (C++11)
bitset::count
Capacity
bitset::size
Modifiers
bitset::operator&=bitset::operator|=bitset::operator^=bitset::operator~
bitset::operator<<=bitset::operator>>=bitset::operator<<bitset::operator>>
bitset::set
bitset::reset
bitset::flip
Conversions
bitset::to_string
bitset::to_ulong
bitset::to_ullong (C++11)
Non-member functions
operator&operator|operator^	operator<<operator>>
Helper classes
std::hash (C++11)

 

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 (C++20)	counts the number of 1 bits in an unsigned integer (function template)