utf8 utf16 convert

utf8_16cvt.cc

std::string utf16_to_utf8(std::u16string const &s) {
  std::wstring_convert<
      std::codecvt_utf8_utf16<char16_t, 0x10ffff,
                              std::codecvt_mode::little_endian>,
      char16_t>
      cnv;
  std::string utf8 = cnv.to_bytes(s);
  if (cnv.converted() < s.size())
    throw std::runtime_error("incomplete conversion");
  return utf8;
}

std::u16string utf8_to_utf16(std::string const &utf8) {
  std::wstring_convert<
      std::codecvt_utf8_utf16<char16_t, 0x10ffff,
                              std::codecvt_mode::little_endian>,
      char16_t>
      cnv;
  std::u16string s = cnv.from_bytes(utf8);
  if (cnv.converted() < utf8.size())
    throw std::runtime_error("incomplete conversion");
  return s;
}
// windows only
// include <windows.h>
std::u16string utf8_to_utf16_windows(std::string const &utf8) {
  int count = MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS, utf8.c_str(),
                                  -1, NULL, 0);
  std::u16string res;
  res.resize(count);
  int flag = MultiByteToWideChar(CP_UTF8, MB_ERR_INVALID_CHARS, utf8.c_str(),
                                 -1, (wchar_t *)(res.data()), count);
  if (!flag) {
    std::cerr << "converted u8 to utf16 failed" << std::endl;
    return u"";
  }
  return res;
}
std::string utf16_to_utf8_windows(std::u16string const &utf16s) {
  int count = WideCharToMultiByte(CP_UTF8, 0, (wchar_t *)(utf16s.c_str()), -1,
                                  NULL, 0, NULL, NULL);
  std::string res;
  res.resize(count);
  int flag = WideCharToMultiByte(CP_UTF8, 0, (wchar_t *)utf16s.c_str(), -1,
                                 res.data(), count, NULL, NULL);
  if (!flag) {
    std::cerr << "converted u16 to utf8 failed" << std::endl;
    return "";
  }
  return res;
}