std::bitset<N>::operator[]
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bool operator[]( std::size_t pos ) const;
(1)
(constexpr since C++11)
reference operator[]( std::size_t pos );
(2)
(constexpr since C++23)
Accesses the bit at position pos.
1) Returns the value of the bit.
2) Returns an object of type std::bitset::reference that allows modification of the value.
If pos < size() is false, the behavior is undefined.
(until C++26)If pos < size() is false:
- If the implementation is hardened, a contract violation occurs. Moreover, if the contract-violation handler returns under "observe" evaluation semantic, the behavior is undefined.
- If the implementation is not hardened, the behavior is undefined.
[edit] Parameters
pos
-
position of the bit to return
[edit] Return value
1) The value of the requested bit.
2) An object of type std::bitset::reference , which allows writing to the requested bit.
[edit] Exceptions
Throws nothing.
[edit] Example
Run this code
#include <bitset> #include <cstddef> #include <iostream> int main() { std::bitset <8> b1{0b00101010}; // binary literal for 42 for (std::size_t i = 0; i < b1.size(); ++i) std::cout << "b1[" << i << "]: " << b1[i] << '\n'; b1[0] = true; // modifies the first bit through bitset::reference std::cout << "After setting bit 0, b1 holds " << b1 << '\n'; }
Output:
b1[0]: 0 b1[1]: 1 b1[2]: 0 b1[3]: 1 b1[4]: 0 b1[5]: 1 b1[6]: 0 b1[7]: 0 After setting bit 0, b1 holds 00101011
[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 11 | C++98 | 1. the description was missing in the C++ standard 2. there was only the non-const overload |
1. description added 2. added the const overload |
| LWG 907 | C++98 | the behavior of reading the bit at pos was equivalent to that of test(pos), but test() may throw exceptions
|
avoids mentioning test()
|