Defines a type of object to be thrown by std::optional::value when accessing an optional object that does not contain a value.
All member functions ofstd::bad_optional_access are constexpr: it is possible to create and use std::bad_optional_access objects in the evaluation of a constant expression.
However, std::bad_optional_access objects generally cannot be constexpr, because any dynamically allocated storage must be released in the same evaluation of constant expression.
Inheritance diagram
[edit] Member functions constructs a newbad_optional_access object
bad_optional_access object
bad_optional_access() noexcept;
(1) (since C++17)bad_optional_access( const bad_optional_access& other ) noexcept;
(2) (since C++17)Constructs a new bad_optional_access object with an implementation-defined null-terminated byte string which is accessible through what().
1) Default constructor.
2)Copy constructor. If
*thisand
otherboth have dynamic type
std::bad_optional_access
then
std::strcmp(what(), other.what()) == 0.
Parameters other - another exception object to copy std::bad_optional_access::operator=bad_optional_access& operator=( const bad_optional_access& other ) noexcept;
(since C++17)Assigns the contents with those of other. If *this and other both have dynamic type std::bad_optional_access then std::strcmp(what(), other.what()) == 0 after assignment.
*this
std::bad_optional_access::whatvirtual const char* what() const noexcept;
(since C++17)Returns the explanatory string.
Return valuePointer 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.
The returned string is encoded with the ordinary literal encoding during constant evaluation.
(since C++26) NotesImplementations are allowed but not required to override what().
std::exception) [edit] returns an explanatory string
std::exception) [edit] [edit] Notes [edit] Example
#include <iostream>
#include <optional>
int main()
{
std::optional<int> opt; // creates an empty optional
try
{
[[maybe_unused]] auto x = opt.value(); // throws
}
catch (const std::bad_optional_access& ex)
{
std::cout << ex.what() << '\n';
}
}
Possible output:
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