std::regex_traits::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 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 character classes are always recognized, in both narrow and wide character forms, 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 | std::ctype classification |
"alnum" | std::ctype_base::alnum |
"alpha" | std::ctype_base::alpha |
"blank" | std::ctype_base::blank |
"cntrl" | std::ctype_base::cntrl |
"digit" | std::ctype_base::digit |
"graph" | std::ctype_base::graph |
"lower" | std::ctype_base::lower |
"print" | std::ctype_base::print |
"punct" | std::ctype_base::punct |
"space" | std::ctype_base::space |
"upper" | std::ctype_base::upper |
"xdigit" | std::ctype_base::xdigit |
"d" | std::ctype_base::digit |
"s" | std::ctype_base::space |
"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 ForwardIterator .
|
Return value
The bitmask representing the character classification determined by the given character class, or char_class_type()
if the class is unknown.
Example
demonstraits a custom regex_traits implementation of lookup_classname/isctype
#include <iostream> #include <locale> #include <regex> #include <cwctype> // 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 kanji 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) |