std::regex_traits::isctype
bool isctype( CharT c, char_class_type f ) const;
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Determines whether the character c
belongs to the character class identified by f
, which, in turn, is a value returned by lookup_classname()
.
The version of this function provided in the standard library specializations of std::regex_traits, first converts f
to some temporary value m
of type std::ctype_base::mask in implementation-defined manner, then attempts to classify the character in the imbued locale by calling std::use_facet<std::ctype<CharT>>(getloc()).is(m, c). If that returned true, true is returned by isctype()
. Otherwise, checks whether c
equals '_'
and the bitmask f
corresponds to the character class [:w:]
, in which case true is returned. Otherwise, false
is returned.
Note: the published standard is phrased incorrectly, requiring this function to return true for '_'
in all cases. This is LWG issue 2018.
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[edit] Parameters
c | - | the character to classify |
f | - | the bitmask obtained from lookup_classname() |
[edit] Return value
true if c
is classified by f
, false otherwise.
[edit] Example
#include <iostream> #include <string> #include <regex> int main() { std::regex_traits<char> t; std::string str_alnum = "alnum"; auto a = t.lookup_classname(str_alnum.begin(), str_alnum.end()); std::string str_w = "w"; // [:w:] is [:alnum:] plus '_' auto w = t.lookup_classname(str_w.begin(), str_w.end()); std::cout << std::boolalpha << t.isctype('A', w) << ' ' << t.isctype('A', a) << '\n' << t.isctype('_', w) << ' ' << t.isctype('_', a) << '\n' << t.isctype(' ', w) << ' ' << t.isctype(' ', a) << '\n'; }
Output:
true true true false false false
[edit] See also
gets a character class by name (public member function) |
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[virtual]
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classifies a character or a character sequence (virtual protected member function of std::ctype )
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