std::experimental::filesystem::path::root_directory
From cppreference.com
                    
                                        
                    < cpp | experimental/fs | path
                    
                                                            
                    | path root_directory() const; | (filesystem TS) | |
Returns the root directory of the path. If the path does not include root name, returns path().
| Contents | 
[edit] Parameters
(none)
[edit] Return value
The root directory of the path.
[edit] Exceptions
(none)
[edit] See also
| returns the root-name of the path, if present (public member function) | |
| returns the root path of the path, if present (public member function) | |