If the character sequence[first, last) represents the name of a valid character class in the currently imbued locale (that is, the string between[: and:] in regular expressions), returns the implementation-defined value representing this character class. Otherwise, returns zero.

If the parametericase istrue, the character class ignores character case, e.g. the regex[:lower:] withstd::regex_constants::icase generates a call tostd::regex_traits<>::lookup_classname() with[first, last) indicating the string"lower" andicase==true. This call returns the same bitmask as the call generated by the regex[:alpha:] withicase==false.

The following narrow and wide character class names are always recognized bystd::regex_traits<char> andstd::regex_traits<wchar_t> respectively, and the classifications returned (withicase==false) correspond to the matching classifications obtained by thestd::ctype facet of the imbued locale, as follows:

The classification returned for the string"w" may be exactly the same as"alnum", in which caseisctype() adds'_' explicitly.

Additional classifications such as"jdigit" or"jkanji" may be provided by system-supplied locales (in which case they are also accessible throughstd::wctype).

[edit]Parameters

[edit]Return value

The bitmask representing the character classification determined by the given character class, orchar_class_type() if the class is unknown.

[edit]Example

#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"}

alnums: 風の谷のナウシカkatakana: ナウシカ

[edit]See also

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