std::experimental::basic_string_view::substr
From cppreference.com
                    
                                        
                    < cpp | experimental | basic string view
                    
                                                            
                    |   constexpr basic_string_view 
substr(size_type pos = 0, size_type count = npos ) const;  | 
||
Returns a view of the substring [pos, pos + rcount), where rcount is the smaller of count and size() - pos.
Contents | 
[edit] Parameters
| pos | - | position of the first character | 
| count | - | requested length | 
[edit] Return value
View of the substring [pos, pos + rcount).
[edit] Exceptions
std::out_of_range if pos >= size()
[edit] Complexity
Constant.
[edit] See also
|    copies characters   (public member function)  | 
|
|    find characters in the view   (public member function)  |