std::error_condition::category
From cppreference.com
                    
                                        
                    < cpp | error | error condition
                    
                                                            
                    | const error_category& category() const; | (since C++11) | |
Returns the stored error category.
Parameters
(none)
Return value
The stored error category.
Exceptions
noexcept specification:  
noexcept