Defining XML Serializable Objects Using Macros

It is often necessary to make your C++ objects serializable to/from XML. It is simple to do so in Java or C#, for example, by using reflection, but not always in C++. It would be interesting to introduce some brief but portable way to describe objects' serializable properties. The prototype presented allows defining XML serializable objects using macros in an MSVC++ 7 unmanaged code attributes-like manner because each serializable object/property needs to be described only once in the class definition, for example:

class CEmployee : public CXmlSerializable
{
public:
   BEGIN_META_MAP(CEmployee)
      META_PROP(CSTLString,     Region)
   END_META_MAP
};


class COrder : public CXmlSerializable
{
   BEGIN_META_MAP(COrder)
      META_PROP(CSTLString,     ShipCity)
      META_PROP(CSTLString,     EmployeeName)
      META_OBJECTS(CEmployee,   Employees)
   END_META_MAP
};

class CCustomer : public CXmlSerializable
{
   BEGIN_META_MAP(CCustomer)
      META_PROP(CSTLString,     CustomerID)
      META_PROP(CSTLString,     ContactName)
      META_OBJECTS(COrder,      Orders)
   END_META_MAP
};

class CCustomersList : public CXmlSerializable
{
   BEGIN_META_MAP(CCustomersList)
      META_OBJECTS(CCustomer,   Customers)
   END_META_MAP
};

Microsoft SAX parser implementation is used here to read XML. The META_PROP and META_OBJECTS macros assemble mapping arrays of helper methods for the parser content handler and the bodies of the objects ToXml() methods.

One small challenge here was finding a way to assemble something like a linked list at compile time to glue properties declarations together. The solution found is to use templatized inner classes along with the __LINE__ ANSI Predefined macro (this code is a part of the META_PROP macro, back slashes at the row ends are omitted here, all the __LINE__ values are equal inside each META_PROP or META_OBJECTS macro):

template<> struct CDescriptor<__LINE__>
{
   enum
   {
      ESetDataFuncPos = CDescriptor<__LINE__-1>::ESetDataFuncPos,
      EAddObjFuncPos  = CDescriptor<__LINE__-1>::EAddObjFuncPos + 1
   };
   static void Setup(CMetaInfo* pInfo)
   {
      CDescriptor<__LINE__-1>::Setup(pInfo);
      pInfo->m_pAddObjFunc[EAddObjFuncPos].first = L#name;
      pInfo->m_pAddObjFunc[EAddObjFuncPos].second =
             ClassAddNew##name;
   }
   ...
};

ClassAddNew##name here is a static inner helper function; it has the next prototype:

typedef bool (* SET_DATA_FUNC)(CXmlSerializable*,
                               const wchar_t*, size_t);

Objects data writing to XML is implemented in the similar manner. Because the

template<typename T>
inline bool Convert(const wchar_t* pwsz, size_t nLength, T& out)

and

template<typename T>
inline void WriteField(std::wostream& s, const T& data)

data exchange functions involved are templatized, they can be customized for specific data types such as COleDateTime or std::vector<BYTE> for binary/image data.

The XS_BASE macro can be manipulated to hide implementation details in the separate data access objects library.

The sample application is intended to demonsrate the mechanism proposed. It just loads an XML document example to the data object and then makes the object write itself to the standard output stream. It's as simple as that (error handling omitted for brevity):

CComPtr<ISAXXMLReader> pSAXXMLReader;
CSAXObjectContentHandlerImpl saxObjectContentHandler;

HRESULT hr = pSAXXMLReader.CoCreateInstance(__uuidof(SAXXMLReader));

hr = pSAXXMLReader->putContentHandler(&saxObjectContentHandler);

CCustomersList customersList;
// add root objects
saxObjectContentHandler.AddRootObject(L"ROOT", &customersList);

hr = pSAXXMLReader->parse(CComVariant(g_pszXml));

std::wostringstream ostr;
customersList.ToXml(ostr);


Downloads

Comments

  • Serializing a class with setter and getter methods

    Posted by gabriel927 on 08/25/2005 12:33pm

    Is there a way to serialize the class with getter and setter methods?  If so, please show me how.

    Reply
Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • When individual departments procure cloud service for their own use, they usually don't consider the hazardous organization-wide implications. Read this paper to learn best practices for setting up an internal, IT-based cloud brokerage function that service the entire organization. Find out how this approach enables you to retain top-down visibility and control of network security and manage the impact of cloud traffic on your WAN.

  • How to give users what they want AND maintain control, visibility, and security. File sync and share is everywhere. In the past decade, cloud-based storage and syncing solutions have exploded to fill a growing need for anytime, anywhere access to everything from photos and videos to documents, spreadsheets, and PDFs. We understand that choosing any new service or tool can be a lengthy and complex process. That's why we've created this buyer's guide to help make your evaluation process a little bit easier. In …

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date