std::bad_variant_access - cppreference.com (original) (raw)

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.

Contents

• 1 Member functions
• 2 std::bad_variant_access::bad_variant_access
  • 2.1 Parameters
• 3 std::bad_variant_access::operator=
  • 3.1 Parameters
  • 3.2 Return value
• 4 std::bad_variant_access::what
  • 4.1 Return value
  • 4.2 Notes
• 5 Inherited from std::exception
  • 5.1 Member functions
  • 5.2 Notes
  • 5.3 Example
  • 5.4 See also

[edit] Member functions

| | constructs a new bad_variant_access object (public member function) | | ------------------------------------------------------------------------ | | | replaces the bad_variant_access object (public member function) | | | returns the explanatory string (public member function) |

std::bad_variant_access::bad_variant_access

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

std::bad_variant_access::operator=

| bad_variant_access& operator=( const bad_variant_access& other ) noexcept; | | (since C++17) (constexpr since C++26) | | ------------------------------------------------------------------------------- | | ------------------------------------- |

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

Return value

*this

std::bad_variant_access::what

| virtual const char* what() const noexcept; | | (since C++17) (constexpr since C++26) | | ------------------------------------------- | | ------------------------------------- |

Returns the explanatory string.

Return value

Pointer 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.

Notes

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

Inherited from std::exception

Member functions

| | destroys the exception object (virtual public member function of std::exception) [edit] | | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | returns an explanatory string (virtual public member function of std::exception) [edit] |

[edit] Notes

[edit] Example

#include #include   int main() { std::variant<int, float> v; v = 12; try { std::get(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 error (function template) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | calls the provided functor with the arguments held by one or more variants (function template) [edit] | | | calls the provided functor with the argument held by the variant (public member function) [edit] | | | exception indicating checked access to an optional that doesn't contain a value (class) [edit] | | | exception indicating checked access to an expected that contains an unexpected value (class template) [edit] |