std::bitset<N>::test
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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[] , it performs a bounds check.
[edit] Parameters
pos
-
position of the bit to return (counting from 0)
[edit] Return value
true if the requested bit is set, false otherwise.
[edit] Exceptions
Throws std::out_of_range if pos does not correspond to a valid bit position.
[edit] 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)
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2250 | C++98 | the behavior was undefined if pos does not correspond to a valid bit position |
always throws an exception in this case |