`bit::vector` — Iterate over the Set Bits

We have methods that iterate over the elements in a bit-vector calling a function f(i) for every index i where the corresponding element is 1.

1constexpr void if_set_call(std::invocable<std::size_t> auto f) const;
2constexpr void reverse_if_set_call(std::invocable<std::size_t> auto f) const;

1: The iteration here is in the order vector.first_set() forward to vector.final_set().
2: The iteration here is in the order vector.final_set() backward to vector.first_set().

In these methods, the f parameter is any function taking an index as its argument. See std::invocable. For each set element index pos, these methods will be called f(pos).

Example

#include <bit/bit.h>
int main()
{
1    bit::vector<> v(11, [&](size_t k) { return (k + 1) % 2; });
    std::cout << "The set indices in " << v << " are ";
2    v.if_set_call([](std::size_t k) { std::cout << k << ' '; });
    std::cout << std::endl;
}

1: Creates a vector of size 11 by calling a lambda that sets all the even indices.
2: The trivial print to std::cout lambda is called if the corresponding element in v is set.

Output

The set indices in [1 0 1 0 1 0 1 0 1 0 1] are 0 2 4 6 8 10

See Also