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)
pub	operator=	replaces the bad_variant_access object (public member function)
pub	what	returns the explanatory string (public member function)

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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

pub	(destructor) [virtual]	destroys the exception object (virtual public member function of std::exception)
pub	what [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