function
<exception>
std::unexpected
[[noreturn]] void unexpected();
Function handling unexpected exceptions
Calls the current unexpected handler.
By default, the unexpected handler calls terminate. But this behavior can be redefined by calling set_unexpected.
This function is automatically called when a function throws an exception that is not listed in its dynamic-exception-specifier (i.e., in its throw specifier).
This function is provided so that the unexpected handler can be explicitly called by a program, and works even if set_unexpected has not been used to set a custom unexpected handler (calling terminate in this case).
Compatibility
The use of dynamic-exception-specifiers is deprecated (since C++11).
Exception safety
Throws an exception if it does not terminate execution of the program.