NAME¶

std::bad_variant_access - std::bad_variant_access

Synopsis¶

Defined in header <variant>
class bad_variant_access : public std::exception (since C++17)

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::visit called to visit a variant that is valueless_by_exception

Member functions¶

constructor constructs a new bad_variant_access object
(public member function)
operator= replaces the bad_variant_access object
(public member function)
what returns the explanatory string
(public member function)

std::bad_variant_access::bad_variant_access

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 *this and other both 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 ) (since C++17)
noexcept;

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¶

other - another exception object to assign with

Return value¶

*this

std::bad_variant_access::what

virtual const char* what() const noexcept; (since C++17)

Returns the explanatory string.

Parameters¶

(none)

Return value¶

Pointer to a 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.

Notes¶

Implementations are allowed but not required to override what().

Inherited from std::exception

Member functions¶

destructor destroys the exception object
[virtual] (virtual public member function of std::exception)
what returns an explanatory string
[virtual] (virtual public member function of std::exception)

Example¶

// Run this code

#include <variant>
#include <iostream>

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

See also¶

std::get(std::variant) reads the value of the variant given the index or the type
(C++17) (if the type is unique), throws on error
(function template)
visit calls the provided functor with the arguments held by one or
(C++17) more variants
(function template)