std::bitset<N>::test

 

C++

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Named requirements

Feature test macros (C++20)

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Concepts library (C++20)

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Diagnostics library

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Filesystem library (C++17)

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Technical specifications

Symbols index

External libraries

 

Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison (C++20) three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)    is_eqis_neqis_ltis_lteqis_gtis_gteq (C++20)(C++20)(C++20)(C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20) bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator> rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)    cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17)

 

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;		(until C++23)
constexpr bool test( std::size_t pos ) const;		(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 << "first set bit 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:

first set bit 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 two (function template)