std::bitset::count - cppreference.com

##### cppreference.com

##### Search

Create account

##### Namespaces

- Page
- Discussion

##### Variants

##### Views

- View
- Edit
- History

##### Actions

# std::bitset::count

From cppreference.com
< cpp‎ | utility‎ | bitset

std::size_t count() const; |  |

Returns the number of bits that are set to true.

### [edit] Parameters

(none)

### [edit] Return value

number of bits that are set to true.

### [edit] Exceptions

(none) | (until C++11)
`noexcept` specification: noexcept | (since C++11)

### [edit] 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
        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

size | returns the size number of bits that the bitset can hold (public member function) [edit]

Retrieved from "http://en.cppreference.com/mwiki/index.php?title=cpp/utility/bitset/count&oldid=91759"
Category:

- unconditionally noexcept

Hidden categories:

- Pages with unreviewed unconditional noexcept template
- Pages with unreviewed noexcept template