std::regex_traits::value(3)

🌸 NAME 🌸

okay bestie, welcome to std::regex_traits::value(3) — the page from the C++ Standard Libary manual (yes, that's literally how it's spelled, iykyk 😭). In classic manpage fashion, the name is also std::regex_traits::value — std::regex_traits::value. It's giving "same name, main character energy" 💅✨

📜 Synopsis 📜

int value( CharT ch, int radix ) const;  (since C++11)

bestie, this one determines the value represented by the digit ch in the numeric base radix, given the currently imbued locale. No cap, 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. It's lowkey the digit detective of regex traits 🔥

💖 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. periodt. If it's not valid, it's a -1 situation and we move on 🫶

🧚 Example 🧚

okay so here's the whole code moment, bestie — run this code and watch the custom traits do their thing 💜

        // Run this code

        #include <iostream>
        #include <locale>
        #include <map>
        #include <regex>

        // 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

source: http://cppreference.com · version/date: 2024.06.10 · page: std::regex_traits::value(3) — and that's the whole manual page, bestie, slay 💖✨🎀