std::bitset<N>::test

 

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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)

 

bool test( std::size_t pos ) const;		(constexpr since C++23)

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

pos

-

position of the bit to return (counting from 0)

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

Run this code

#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';
    }
}

Possible output:

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

See also

operator[]	accesses specific bit (public member function)
popcount (C++20)	counts the number of 1 bits in an unsigned integer (function template)
has_single_bit (C++20)	checks if a number is an integral power of 2 (function template)