std::bad_optional_access
<optional>
Defines a type of object to be thrown by std::optional::value when accessing an optional object that does not contain a value.
std::bad_optional_access are constexpr: it is possible to create and use std::bad_optional_access objects in the evaluation of a constant expression.However, std::bad_optional_access objects generally cannot be constexpr, because any dynamically allocated storage must be released in the same evaluation of constant expression.
Inheritance diagram
Contents
[edit] Member functions
bad_optional_access object (public member function)
bad_optional_access object (public member function)
(public member function)
std::bad_optional_access::bad_optional_access
(constexpr since C++26)
(constexpr since C++26)
Constructs a new bad_optional_access object with an implementation-defined null-terminated byte string which is accessible through what().
std::bad_optional_access then std::strcmp (what(), other.what()) == 0.Parameters
std::bad_optional_access::operator=
(constexpr since C++26)
Assigns the contents with those of other. If *this and other both have dynamic type std::bad_optional_access then std::strcmp (what(), other.what()) == 0 after assignment.
Parameters
Return value
*this
std::bad_optional_access::what
(constexpr since C++26)
Returns the explanatory string.
Return value
Pointer to an implementation-defined null-terminated string with explanatory information. The string is suitable for conversion and display as a std::wstring . The pointer is guaranteed to be valid at least until the exception object from which it is obtained is destroyed, or until a non-const member function (e.g. copy assignment operator) on the exception object is called.
The returned string is encoded with the ordinary literal encoding during constant evaluation.
(since C++26)Notes
Implementations are allowed but not required to override what().
Inherited from std::exception
Member functions
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_constexpr_exceptions |
202502L |
(C++26) | constexpr std::bad_optional_access
|
[edit] Example
#include <iostream> #include <optional> int main() { std::optional <int> opt; // creates an empty optional try { [[maybe_unused]] auto x = opt.value(); // throws } catch (const std::bad_optional_access& ex) { std::cout << ex.what() << '\n'; } }
Possible output:
bad optional access
[edit] See also
expected that contains an unexpected value (class template) [edit]