std::bitset<N>:: test

Returns the value of the bit at the position pos (counting from 0).

Unlike operator[] , performs a bounds check and throws std::out_of_range if pos does not correspond to a valid position in the bitset.

Parameters

Return value

true if the requested bit is set, false otherwise.

Exceptions

std::out_of_range if pos does not correspond to a valid position within the bitset.

Example

#include <bit>
#include <bitset>
#include <cassert>
#include <iostream>
#include <stdexcept>
 
int main()
{
    std::bitset<10> b1("1111010000");
 
    std::size_t idx = 0;
    while (idx < b1.size() && !b1.test(idx))
        ++idx;
 
    assert(static_cast<int>(idx) == std::countr_zero(b1.to_ulong()));
 
    if (idx < b1.size())
        std::cout << "The first set bit is at index " << idx << '\n';
    else
        std::cout << "no set bits\n";
 
    try
    {
        std::bitset<0B10'1001'1010> bad;
        if (bad.test(bad.size()))
            std::cout << "Expect unexpected!\n";
    }
    catch (std::out_of_range const& ex)
    {
        std::cout << "Exception: " << ex.what() << '\n';
    }
}

The first set bit is at index 4
Exception: bitset::test: __position (which is 666) >= _Nb (which is 666)

See also