std::exception::what
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | virtual const char* what() const throw(); | (until C++11) | |
| virtual const char* what() const noexcept; | (since C++11) | |
Returns the explanatory string.
Parameters
(none)
Return value
Pointer to a null-terminated string with explanatory information. 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 on the exception object is called.