std::regex_traits<CharT>::lookup_classname
| template< class ForwardIt > char_class_type lookup_classname( ForwardIt first, |
||
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 parameter icase is true, the character class ignores character case, e.g. the regex [:lower:] with std::regex_constants::icase generates a call to std::regex_traits<>::lookup_classname() with [first, last) indicating the string "lower" and icase == true. This call returns the same bitmask as the call generated by the regex [:alpha:] with icase == false.
The following narrow and wide character class names are always recognized by std::regex_traits<char> and std::regex_traits<wchar_t> respectively, and the classifications returned (with icase == false) correspond to the matching classifications obtained by the std::ctype facet of the imbued locale, as follows:
| Character class name | std::ctype classification | |
|---|---|---|
| Narrow | Wide | |
| "alnum" | L"alnum" | std::ctype_base::alnum |
| "alpha" | L"alpha" | std::ctype_base::alpha |
| "blank" | L"blank" | std::ctype_base::blank |
| "cntrl" | L"cntrl" | std::ctype_base::cntrl |
| "digit" | L"digit" | std::ctype_base::digit |
| "graph" | L"graph" | std::ctype_base::graph |
| "lower" | L"lower" | std::ctype_base::lower |
| "print" | L"print" | std::ctype_base::print |
| "punct" | L"punct" | std::ctype_base::punct |
| "space" | L"space" | std::ctype_base::space |
| "upper" | L"upper" | std::ctype_base::upper |
| "xdigit" | L"xdigit" | std::ctype_base::xdigit |
| "d" | L"d" | std::ctype_base::digit |
| "s" | L"s" | std::ctype_base::space |
| "w" | L"w" | std::ctype_base::alnum with '_' optionally added |
The classification returned for the string "w" may be exactly the same as "alnum", in which case isctype() adds '_' explicitly.
Additional classifications such as "jdigit" or "jkanji" may be provided by system-supplied locales (in which case they are also accessible through std::wctype).
Parameters
| first, last | - | a pair of iterators which determines the sequence of characters that represents a name of a character class |
| icase | - | if true, ignores the upper/lower case distinction in the character classification |
| Type requirements | ||
-ForwardIt must meet the requirements of LegacyForwardIterator.
| ||
Return value
The bitmask representing the character classification determined by the given character class, or char_class_type() if the class is unknown.
Example
Demonstrates a custom regex traits implementation of lookup_classname() / isctype():
#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
See also
| indicates membership in a character class (public member function) | |
| looks up a character classification category in the current C locale (function) |