Encoding conversion in C++

string-conversion.cpp

// Convert a UTF-16 string to an ANSI string.
std::string utf16ToAnsi(const std::wstring &wstr) {
   int length = static_cast<int>(wstr.length());
   if (!length) return std::string();

   DWORD flags = WC_NO_BEST_FIT_CHARS;
   int bufSize = WideCharToMultiByte(CP_ACP, flags, &wstr[0], length, NULL, 0, NULL, NULL);
   if (bufSize > 0) {
      std::string strTo(bufSize, 0);
      WideCharToMultiByte(CP_ACP, flags, &wstr[0], length, &strTo[0], bufSize, NULL, NULL);
      return strTo;
   }
   return std::string();
}

// Convert a UTF-16 string to an UTF-8 string.
std::string utf16ToUtf8(const std::wstring &wstr) {
   int length = static_cast<int>(wstr.length());
   if (!length) return std::string();

   DWORD flags = WC_ERR_INVALID_CHARS;
   int bufSize = WideCharToMultiByte(CP_UTF8, flags, &wstr[0], length, NULL, 0, NULL, NULL);
   if (bufSize > 0) {
      std::string strTo(bufSize, 0);
      WideCharToMultiByte(CP_UTF8, flags, &wstr[0], length, &strTo[0], bufSize, NULL, NULL);
      return strTo;
   }
   return std::string();
}

// Convert a UTF-8 string to a UTF-16 string.
std::wstring utf8ToUtf16(const std::string &str) {
   int length = static_cast<int>(str.length());
   if (!length) return std::wstring();

   DWORD flags = MB_ERR_INVALID_CHARS;
   int bufSize = MultiByteToWideChar(CP_UTF8, flags, &str[0], length, NULL, 0);
   if (bufSize > 0) {
      std::wstring wstrTo(bufSize, 0);
      MultiByteToWideChar(CP_UTF8, flags, &str[0], length, &wstrTo[0], bufSize);
      return wstrTo;
   }
   return std::wstring();
}

// Convert a UTF-8 string to an ANSI string.
std::string utf8ToAnsi(const std::string &str) {
   return utf16ToAnsi(utf8ToUtf16(str));
}

// Convert an ANSI string to a UTF-16 string.
std::wstring ansiToUtf16(const std::string &str) {
   int length = static_cast<int>(str.length());
   if (!length) return std::wstring();

   DWORD flags = MB_ERR_INVALID_CHARS;
   int bufSize = MultiByteToWideChar(CP_ACP, flags, &str[0], length, NULL, 0);
   if (bufSize > 0) {
      std::wstring wstrTo(bufSize, 0);
      MultiByteToWideChar(CP_ACP, flags, &str[0], length, &wstrTo[0], bufSize);
      return wstrTo;
   }
   return std::wstring();
}

// Convert an ANSI string to a UTF-8 string.
std::string ansiToUtf8(const std::string &str) {
   return utf16ToUtf8(ansiToUtf16(str));
}