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
true if *this represents the result of a failed match, false otherwise, i.e. size() == 0.
Exceptions
May throw implementation-defined exceptions.
Complexity
Constant.
See also
| returns the number of matches in a fully-established result state (public member function) |