std::regex_traits::isctype - cppreference.com (original) (raw)

| bool isctype( CharT c, char_class_type f ) const; | | | | --------------------------------------------------- | | |

Determines whether the character c belongs to the character class identified by f, 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::regex_traits does the following:

For each std::ctype category listed in the table in the page lookup_classname(), if the bits in f corresponding to the category are set, the corresponding bits in m will also be set.

1. Then attempts to classify the character in the imbued locale by calling std::use_facet<std::ctype<CharT>>(getloc()).is(m, c).

• If that returns true, isctype() will also return true.
• Otherwise, if c equals '_', and f includes the result of calling lookup_classname() for the character class [:w:], true is returned, otherwise false is returned.

[edit] Parameters

[edit] Return value

true if c is classified by f, false otherwise.

[edit] Example

#include #include #include   int main() { std::regex_traits 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

Demonstrates a custom regex traits implementation of lookup_classname() / isctype():

#include #include #include #include   // This custom regex traits uses wctype/iswctype to implement lookup_classname/isctype. struct wctype_traits : std::regex_traits { using char_class_type = std::wctype_t;   template char_class_type lookup_classname(It first, It last, bool = false) const { return std::wctype(std::string(first, last).c_str()); }   bool isctype(wchar_t c, char_class_type f) const { return std::iswctype(c, f); } };   int main() { std::locale::global(std::locale("ja_JP.utf8")); std::wcout.sync_with_stdio(false); std::wcout.imbue(std::locale());   std::wsmatch m; std::wstring in = L"風の谷のナウシカ"; // matches all characters (they are classified as alnum) std::regex_search(in, m, std::wregex(L"([[:alnum:]]+)")); std::wcout << "alnums: " << m[1] << '\n'; // prints "風の谷のナウシカ" // matches only the katakana std::regex_search(in, m, std::basic_regex<wchar_t, wctype_traits>(L"([[:jkata:]]+)")); std::wcout << "katakana: " << m[1] << '\n'; // prints "ナウシカ" }

Output:

alnums: 風の谷のナウシカ katakana: ナウシカ

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also

| | gets a character class by name (public member function) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | classifies a character or a character sequence (virtual protected member function of std::ctype) [edit] | | | classifies a wide character according to the specified LC_CTYPE category (function) [edit] |