std::bitset::count - cppreference.com (original) (raw)

| | (noexcept since C++11) (constexpr since C++23) | | ------------------------------------------------- |

Returns the number of bits that are set to true.

[edit] Return value

Number of bits that are set to true.

[edit] Example

#include #include   constexpr auto popcount(unsigned x) noexcept { unsigned num{}; for (; x; ++num, x &= (x - 1)); return num; } static_assert(popcount(0b101010) == std::bitset<8>{0b101010}.count());   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

[edit] See also

| | returns the number of bits that the bitset holds (public member function) [edit] | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | counts the number of 1 bits in an unsigned integer (function template) [edit] |