UTF-8/16/32 C++ library

This is the C++11 template based header only library under Windows/Linux/MacOs to convert UFT-8/16/32 symbols and strings. The library transparently support wchar_t as UTF-16 for Windows and UTF-32 for Linux and MacOs.

UTF-8 and UTF-32 (UCS-32) both support 31 bit wide code points [0‥0x7FFFFFFF]with no restriction. UTF-16 supports only unicode code points [0‥0x10FFFF], where high [0xD800‥0xDBFF] and low [0xDC00‥0xDFFF] surrogate regions are prohibited.

The maximum UTF-16 symbol size is 2 words (4 bytes, both words should be in the surrogate region). UFT-32 (UCS-32) is always 1 word (4 bytes). UTF-8 has the maximum symbol size (see conversion table for details):

4 bytes for unicode code points
6 bytes for 31bit code points

UTF-16 surrogate decoder:

High\Low	DC00	DC01	…	DFFF
D800	010000	010001	…	0103FF
D801	010400	010401	…	0107FF
⋮	⋮	⋮	⋱	⋮
DBFF	10FC00	10FC01	…	10FFFF

Supported compilers

Tested on following compilers:

Usage example

    // यूनिकोड
    static char const u8s[] = "\xE0\xA4\xAF\xE0\xA5\x82\xE0\xA4\xA8\xE0\xA4\xBF\xE0\xA4\x95\xE0\xA5\x8B\xE0\xA4\xA1";
    using namespace ww898::utf;
    std::u16string u16;
    convz<utf_selector_t<decltype(*u8s)>, utf16>(u8s, std::back_inserter(u16));
    std::u32string u32;
    conv<utf16, utf_selector_t<decltype(u32)::value_type>>(u16.begin(), u16.end(), std::back_inserter(u32));
    std::vector<char> u8;
    convz<utf32, utf8>(u32.data(), std::back_inserter(u8));
    std::wstring uw;
    conv<utf8, utfw>(u8s, u8s + sizeof(u8s), std::back_inserter(uw));
    auto u8r = conv<char>(uw);
    auto u16r = conv<char16_t>(u16);
    auto uwr = convz<wchar_t>(u8s);

    auto u32r = conv<char32_t>(std::string_view(u8r.data(), u8r.size())); // C++17 only

    static_assert(std::is_same<utf_selector<decltype(*u8s)>, utf_selector<decltype(u8)::value_type>>::value, "Fail");
    static_assert(
        std::is_same<utf_selector_t<decltype(u16)::value_type>, utf_selector_t<decltype(uw)::value_type>>::value !=
        std::is_same<utf_selector_t<decltype(u32)::value_type>, utf_selector_t<decltype(uw)::value_type>>::value, "Fail");