cpp/regex/regex traits/isctype

Determines whether the character belongs to the character class identified by, which, in turn, is a value returned by lookup_classname or a bitwise OR of several such values.

The version of this function provided in the standard library specializations of std does the following:

@1@ First converts to some temporary value  of type std in implementation-defined manner

@2@ Then attempts to classify the character in the imbued locale by calling. If that returned, is returned by.

@3@ Otherwise, checks whether equals  and the bitmask  includes  the result of calling lookup_classname for the character class, in which case  is returned.

@4@ Otherwise, is returned.

Return value
if is classified by,  otherwise.