std::char_traits::eq, std::char_traits::lt
From cppreference.com
                    
                                        
                    < cpp | string | char traits
                    
                                                            
                    | (1) | ||
|   static bool eq( char_type a, char_type b );  | 
(until C++11) | |
|   static constexpr bool eq( char_type a, char_type b );  | 
(since C++11) | |
| (2) | ||
|   static bool lt( char_type a, char_type b );  | 
(until C++11) | |
|   static constexpr bool lt( char_type a, char_type b );  | 
(since C++11) | |
Compares two characters.
1) Compares 
a and b for equality.2) Compares 
a and b in such a way that they are totally ordered.Contents | 
[edit] Parameters
| a, b | - | character values to compare | 
[edit] Return value
1) true if 
a and b are equal, false otherwise.2) true if 
a is less than b, false otherwise.[edit] Exceptions
| (since C++11) | 
[edit] Complexity
Constant.