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std::bad_variant_access

Defined in header <variant>.

C++17

class bad_variant_access : public std::exception;

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

pub(constructor)constructs a new bad_variant_access object
(public member function)
puboperator=replaces the bad_variant_access object
(public member function)
pubwhatreturns 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.
    1. 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

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

Example

#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 Result
bad_variant_access

std::bad_variant_access

Defined in header <variant>.

C++17

class bad_variant_access : public std::exception;

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

pub(constructor)constructs a new bad_variant_access object
(public member function)
puboperator=replaces the bad_variant_access object
(public member function)
pubwhatreturns 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.
    1. 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

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

Example

#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 Result
bad_variant_access