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std::bad_expected_access

Defined in header `<expected>`
template< class E > class bad_expected_access : public std::bad_expected_access<void>	(1)	(since C++23)
template<> class bad_expected_access<void> : public std::exception	(2)	(since C++23)

1) Defines a type of object to be thrown by std::expected::value when accessing an expected object that contains an unexpected value. bad_expected_access<E> stores a copy of the unexpected value.

2) bad_expected_access<void> is the base class of all other bad_expected_access specializations.

Members of the primary template

(constructor)	constructs a `bad_expected_access` object (public member function)
error	returns the stored value (public member function)
what	returns the explanatory string (public member function)

std::bad_expected_access::bad_expected_access

explicit bad_expected_access( E e );

Constructs a new bad_expected_access<E> object. Initializes the stored value with std::move(e).

std::bad_expected_access::error

const E& error() const & noexcept;
E& error() & noexcept;
const E&& error() const && noexcept;
E&& error() && noexcept;

Returns a reference to the stored value.

std::bad_expected_access::what

const char* what() const noexcept override;

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().

Members of the `bad_expected_access<void>` specialization

(constructor)	constructs a `bad_expected_access<void>` object (protected member function)
(destructor)	destroys the `bad_expected_access<void>` object (protected member function)
operator=	replaces the `bad_expected_access<void>` object (protected member function)
what	returns the explanatory string (public member function)

Special member functions of bad_expected_access<void> are protected. They can only be called by derived classes.

Example

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