std::nested_exception::nested_ptr
From cppreference.com
                    
                                        
                    < cpp | error | nested exception
                    
                                                            
                    |   std::exception_ptr nested_ptr() const noexcept;  | 
(since C++11) | |
Returns a pointer to the stored exception, if any.
Parameters
(none)
Return value
A std::exception_ptr to the stored exception if one is stored, default-initialized std::exception_ptr otherwise.