std::system_error::what
From cppreference.com
                    
                                        
                    < cpp | error | system error
                    
                                                            
                    | virtual const char* what() const; | (since C++11) | |
Returns the explanatory string.
| Contents | 
[edit] Parameters
(none)
[edit] Return value
Pointer to a null-terminated string with explanatory information.
[edit] Exceptions
noexcept specification:  
noexcept
  [edit] See also
| returns error code (public member function) | 


