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{returnstd::wctype(std::string(first, last).c_str());} bool isctype(wchar_t c, char_class_type f)const{returnstd::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 katakanastd::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) |
