std::bad_variant_access
<variant>
std::bad_variant_access is the type of the exception thrown in the following situations:
- std::get(std::variant) called with an index or type that does not match the currently active alternative.
-
std::visitcalled to visit avariantthat isvalueless_by_exception.
-
std::variant::visitcalled to visit avariantthat isvalueless_by_exception.
std::bad_variant_access are constexpr: it is possible to create and use std::bad_variant_access objects in the evaluation of a constant expression.However, std::bad_variant_access objects generally cannot be constexpr, because any dynamically allocated storage must be released in the same evaluation of constant expression.
Contents
[edit] Member functions
bad_variant_access object (public member function)
bad_variant_access object (public member function)
(public member function)
std::bad_variant_access::bad_variant_access
(constexpr since C++26)
(constexpr since C++26)
Constructs a new bad_variant_access object with an implementation-defined null-terminated byte string which is accessible through what().
std::bad_variant_access then std::strcmp (what(), other.what()) == 0.Parameters
std::bad_variant_access::operator=
(constexpr since C++26)
Assigns the contents with those of other. If *this and other both have dynamic type std::bad_variant_access then std::strcmp (what(), other.what()) == 0 after assignment.
Parameters
Return value
*this
std::bad_variant_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_variant_access
|
[edit] Example
#include <iostream> #include <variant> int main() { std::variant <int, float> v; v = 12; try { std::get<float>(v); } catch (const std::bad_variant_access& e) { std::cout << e.what() << '\n'; } }
Possible output:
bad_variant_access
[edit] See also
(function template) [edit]
variants (function template) [edit]
variant (public member function) [edit]
(class) [edit]
expected that contains an unexpected value (class template) [edit]