c++ 各种类型字符串转换

typedef std::string u8string;

u8string To_UTF8(const std::u16string &s)
{
    std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> conv;
    return conv.to_bytes(s);
}

u8string To_UTF8(const std::u32string &s)
{
    std::wstring_convert<std::codecvt_utf8<char32_t>, char32_t> conv;
    return conv.to_bytes(s);
}

std::u16string To_UTF16(const u8string &s)
{
    std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> conv;
    return conv.from_bytes(s);
}

std::u16string To_UTF16(const std::u32string &s)
{
    std::wstring_convert<std::codecvt_utf16<char32_t>, char32_t> conv;
    std::string bytes = conv.to_bytes(s);
    return std::u16string(reinterpret_cast<const char16_t*>(bytes.c_str()), bytes.length()/sizeof(char16_t));
}

std::u32string To_UTF32(const u8string &s)
{
    std::wstring_convert<codecvt_utf8<char32_t>, char32_t> conv;
    return conv.from_bytes(s);
}

std::u32string To_UTF32(const std::u16string &s)
{
    const char16_t *pData = s.c_str();
    std::wstring_convert<std::codecvt_utf16<char32_t>, char32_t> conv;
    return conv.from_bytes(reinterpret_cast<const char*>(pData), reinterpret_cast<const char*>(pData+s.length()));
}