std::ctype<char>::is
From cppreference.com
                    
                                        
                    < cpp | locale | ctype char
                    
                                                            
                    |   Defined in header  <locale>
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|   bool is(mask m, char c) const;  | 
(1) | |
|   const char* is(const char* low, const char* high, mask* vec) const;  | 
(2) | |
1) Checks if the character 
c is classified by the mask m according to the classification table returned by the member function table(). Effectively calculates table()[(unsigned char)c] & m2) For every character in the character array 
[low, high), reads its full classification mask from the classification table returned by the member function table() (that is, evaluates table()[ (unsigned char)*p] and stores it in the corresponding element of the array pointed to by vecIf (unsigned char)c >= std::ctype<char>::table_size, then an implementation-defined value is substituted instead of table()[(unsigned char)c], possibly different for different values of c.
Parameters
| c | - | character to classify | 
| m | - | mask to use for classifying a single character | 
| low | - | pointer to the first character in an array of characters to classify | 
| high | - | one past the end pointer for the array of characters to classify | 
| vec | - | pointer to the first element of the array of masks to fill | 
Return value
1) true if 
c is classified by m in table()2) 
highNotes
Unlike the primary template std::ctype, this specialization does not perform a virtual function call when classifying characters. To customize the behavior, a derived class may provide a non-default classification table to the base class constructor.
Example
| This section is incomplete Reason: no example  | 
See also
|    [virtual]  | 
   classifies a character or a character sequence   (virtual protected member function of std::ctype<CharT>)  |