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)  | 
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