std::bad_variant_access is the type of the exception thrown in the following situations:
std::visit called to visit a variant that is valueless_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.
bad_variant_access object
bad_variant_access object
bad_variant_access() noexcept;
(1) (since C++17)bad_variant_access( const bad_variant_access& other ) noexcept;
(2) (since C++17)Constructs a new bad_variant_access object with an implementation-defined null-terminated byte string which is accessible through what().
1) Default constructor.
2)Copy constructor. If
*thisand
otherboth have dynamic type
std::bad_variant_access
then
std::strcmp(what(), other.what()) == 0.
Parameters other - another exception object to copy std::bad_variant_access::operator=bad_variant_access& operator=( const bad_variant_access& other ) noexcept;
(since C++17)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.
*this
std::bad_variant_access::whatvirtual const char* what() const noexcept;
(since C++17)Returns the explanatory string.
Return valuePointer 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) NotesImplementations are allowed but not required to override what().
std::exception) [edit] returns an explanatory string
std::exception) [edit] [edit] Notes [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:
[edit] See also reads the value of the variant given the index or the type (if the type is unique), throws on errorvariants
variant
expected that contains an unexpected value
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