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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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