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