std::regex_traits::value
From cppreference.com
< cpp | regex | regex traits
| int value( CharT ch, int radix ) const; |
(since C++11) | |
Determines the value represented by the digit ch in the numeric base radix, given the currently imbued locale. This function is called by std::regex when processing Quantifiers such as {1} or {2,5}, Backreferences such as \1, and hexadecimal and Unicode character escapes.
Parameters
| ch | - | the character that may represent a digit |
| radix | - | either 8, 10, or 16 |
Return value
The numeric value if ch indeed represents a digit in the currently imbued locale that is valid for the numeric base radix, or -1 on error.
Example
Run this code
#include <iostream> #include <locale> #include <regex> #include <map> // This custom regex traits allows japanese numerals struct jnum_traits : std::regex_traits<wchar_t> { static std::map<wchar_t, int> data; int value(wchar_t ch, int radix ) const { wchar_t up = std::toupper(ch, getloc()); return data.count(up) ? data[up] : regex_traits::value(ch, radix); } }; std::map<wchar_t, int> jnum_traits::data = {{L'〇',0}, {L'一',1}, {L'二',2}, {L'三',3}, {L'四',4}, {L'五',5}, {L'六',6}, {L'七',7}, {L'八',8}, {L'九',9}, {L'Ａ',10}, {L'Ｂ',11}, {L'Ｃ',12}, {L'Ｄ',13}, {L'Ｅ',14}, {L'Ｆ',15}}; int main() { std::locale::global(std::locale("ja_JP.utf8")); std::wcout.sync_with_stdio(false); std::wcout.imbue(std::locale()); std::wstring in = L"風"; if(std::regex_match(in, std::wregex(L"\\u98a8"))) std::wcout << "\\u98a8 matched " << in << '\n'; if(std::regex_match(in, std::basic_regex<wchar_t, jnum_traits>(L"\\u九八ａ八"))) std::wcout << L"\\u九八ａ八 with custom traits matched " << in << '\n'; }
Output:
\u98a8 matched 風 \u九八ａ八 with custom traits matched 風