std::exception::what
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | virtual const char* what() const; | ||
Returns the explanatory string.
[edit] Parameters
(none)
[edit] 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.
[edit] Exceptions
| (none) | (until C++11) | 
| noexcept specification:   noexcept | (since C++11) | 


