#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';}

true truetrue falsefalse false

#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