std::regex_traits<CharT>::isctype
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< cpp | regex | regex traits
| 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.
2) 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.
Contents |
[edit] Parameters
| c | - | the character to classify |
| f | - | the bitmask obtained from one or several calls to lookup_classname() |
[edit] Return value
true if c is classified by f, false otherwise.
[edit] Example
Run this code
#include <iostream> #include <regex> #include <string> 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
Demonstrates a custom regex traits implementation of lookup_classname() / isctype():
Run this code
#include <cwctype> #include <iostream> #include <locale> #include <regex> // This custom regex traits uses wctype/iswctype to implement lookup_classname/isctype. struct wctype_traits : std::regex_traits<wchar_t> { using char_class_type = std::wctype_t; template<class It> 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.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2018 | C++11 | the value of m was unspecified | matches lookup_classname()'s minimal support |
[edit] See also
| gets a character class by name (public member function) | |
| [virtual] |
classifies a character or a character sequence (virtual protected member function of std::ctype<CharT>)
|
classifies a wide character according to the specified LC_CTYPE category (function) |
