std::bad_variant_access

 

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std::variant

Member functions

variant::variant

variant::~variant

variant::operator=

Observers

variant::index

variant::valueless_by_exception

Modifiers

variant::emplace

variant::swap

Non-member functions

visit

holds_alternative

get

get_if

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)

swap

Helper classes

monostate

bad_variant_access

variant_size

variant_alternative

hash

Helper objects

variant_npos

 

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 ) 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.

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) [virtual]	destroys the exception object (virtual public member function of std::exception)
what [virtual]	returns an explanatory string (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) (C++17)	reads the value of the variant given the index or the type (if the type is unique), throws on error (function template)
visit (C++17)	calls the provided functor with the arguments held by one or more variants (function template)