std::match_results<BidirIt,Alloc>::empty
From cppreference.com
                    
                                        
                    < cpp | regex | match results
                    
                                                            
                    |   bool empty() const;  | 
 (since C++11)  (until C++20)  | 
|
|   [[nodiscard]] bool empty() const;  | 
(since C++20) | |
Checks whether the match was successful.
Parameters
(none)
Return value
size() == 0 (false if *this represents the result of a successful match, true otherwise)
Exceptions
(none)
Complexity
Constant.
See also
|    returns the number of matches in a fully-established result state  (public member function)  |