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A serialization primer - Part 1

, 25 Nov 2002 CPOL
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This tutorial describes how to easily serialize a simple object.

This article is the first of a 3 part tutorial on serialization.

  • Part 1 introduces the basics of serialization.
  • Part 2 explains how to gracefully handle reading invalid data stores and support versioning.
  • Part 3 describes how to serialize complex objects.

Serialization is the process of writing or reading an object to or from a persistent storage medium, such as a disk file. Serializing an object requires 3 ingredients:

  • A CFile object representing the datafile
  • A CArchive object that provides the serialization context
  • The object being serialized
Serialization data flow

Step 1 - Open the datafile

To serialize an object to the file "foo.dat", open the file with the appropriate access mode. In this example, the file is opened for exclusive read/write access.
  // Open file "foo.dat"
  CFile* pFile = new CFile();
  ASSERT (pFile != NULL);
  if (!pFile->Open ("foo.dat", CFile::modeReadWrite | CFile::shareExclusive)) {
      // Handle error
      return;
  }

Step 2 - Hook up the archive

Next, a CArchive object is hooked up to the file. The archive provides an efficient conduit to persistent storage. Instead of directly reading and writing the file, you serialize data to and from the archive. The archive needs to know if you're going to be using it to read or write data. In this example, we'll assume we're writing data.
  // Create archive ...
  bool bReading = false;  // ... for writing
  CArchive* pArchive = NULL;
  try
  {
    pFile->SeekToBegin();
    UINT uMode = (bReading ? CArchive::load : CArchive::store);
    pArchive = new CArchive (pFile, uMode);
    ASSERT (pArchive != NULL);
  }
  catch (CException* pException)
  {
    // Handle error
    return;
  }

Step 3 - Serialize the object

Finally, we serialize the object by calling its serialize() method. serialize() is just a method we made up. It has nothing to with MFC's CObject::Serialize(). Also, you don't have to derive your object from CObject. Our serialize() method takes a pointer to a CArchive and returns an integer status.
  int CFoo::serialize
    (CArchive* pArchive)
  {
    int nStatus = SUCCESS;

    // Serialize the object ...
    ...
    
    return (nStatus);
  }
We'll get to the actual serialization process in a minute. Meanwhile, let's recognize a couple of important points:
  • The same method CFoo::serialize() is used to read/write the object from/to persistent storage.
  • CFoo::serialize() doesn't know anything about the datafile bring accessed.
Assume CFoo represents an employee record that contains a couple of data members.
  class CFoo
  {
    // Construction/destruction
    public:
      CFoo::CFoo();
      virtual CFoo::~CFoo();

    // Methods
    public:
      int serialize (CArchive* pArchive);

    // Data members
    public:
      CString  m_strName;  // employee name
      int      m_nId;      // employee id
  };
We use CArchive's streaming operators << and >> to read/write the data members from/to the archive. CArchive knows how to serialize simple data types like int, float, DWORD, and objects like CString. The archive also knows whether it's in read or write mode. You can query its mode by calling CArchive::IsStoring(). CFoo's serialization method can then be written as:
  int CFoo::serialize
    (CArchive* pArchive)
  {
    int nStatus = SUCCESS;

    // Serialize the object ...
    ASSERT (pArchive != NULL);
    try
    {
      if (pArchive->IsStoring()) {
         // Write employee name and id
         (*pArchive) << m_strName;
         (*pArchive) << m_nId;
      }
      else {
         // Read employee name and id
         (*pArchive) >> m_strName;
         (*pArchive) >> m_nId;
      }
    }
    catch (CException* pException)
    {
      nStatus = ERROR;
    }
    return (nStatus);
  }

Step 4 - Clean up

When you've finished serializing, you should clean up by closing the archive and datafile.
  pArchive->Close();
  delete pArchive;
  pFile->Close();
  delete pFile();

Conclusion

Well, there you have it - serialization in a (very small) nutshell. In Part 2, we'll see how to gracefully handle reading invalid data stores and support different versions of our object. In Part 3, we'll see how to serialize complex objects.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Ravi Bhavnani
Technical Lead
Canada Canada
Ravi Bhavnani is an ardent fan of Microsoft technologies who loves building Windows apps, especially PIMs, system utilities, and things that go bump on the Internet. During his career, Ravi has developed expert systems, desktop imaging apps, marketing automation software, EDA tools, a platform to help people find, analyze and understand information, trading software for institutional investors and advanced data visualization solutions. He currently works for a company that provides enterprise workforce management solutions to large clients.
 
His interests include the .NET framework, reasoning systems, financial analysis and algorithmic trading, NLP, HCI and UI design. Ravi holds a BS in Physics and Math and an MS in Computer Science and was a Microsoft MVP (C++ and C# in 2006 and 2007). He is also the co-inventor of 2 patents on software security and generating data visualization dashboards. His claim to fame is that he crafted CodeProject's "joke" forum post icon.
 
Ravi's biggest fear is that one day he might actually get a life, although the chances of that happening seem extremely remote.
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Comments and Discussions

 
GeneralRe: About the contents of the file Pinmembercristitomi13-Feb-07 2:22 
GeneralRe: About the contents of the file PinmemberRavi Bhavnani13-Feb-07 3:25 
Generaltrouble in reading in serialized list structures Pinsussitsh1115-Dec-04 12:01 
GeneralRe: trouble in reading in serialized list structures(typo corrected) Pinmemberitsh1116-Dec-04 4:11 
GeneralReading a file using serialization Pinsusshemanth_phk9-Sep-04 11:55 
GeneralRe: Reading a file using serialization PinmemberRavi Bhavnani9-Sep-04 12:28 
GeneralRe: Reading a file using serialization PinmemberThomas Mielke11-Oct-07 14:58 
GeneralCArchive and .NET PinsussDaniel S. Horwitz12-Jul-04 6:37 
GeneralIn memory serialization Pinmemberno_reg_name7-May-04 2:59 
GeneralRe: In memory serialization PinmemberRavi Bhavnani7-May-04 6:02 
GeneralSerialization using Dialog application PinmemberHybridLlama12-Jan-04 16:57 
GeneralRe: Serialization using Dialog application PinmemberRavi Bhavnani16-Jan-04 6:37 
GeneralRe: Serialization using Dialog application PinmemberHybridLlama16-Jan-04 9:56 
GeneralRe: Serialization using Dialog application PinmemberRavi Bhavnani17-Jan-04 3:32 
GeneralRe: Serialization using Dialog application PinmemberHybridLlama17-Jan-04 8:28 
GeneralDitching.NET serialization in favor of MFC PinmemberMtnBiknGuy28-Aug-03 16:49 
GeneralRe: Ditching.NET serialization in favor of MFC PinmemberRavi Bhavnani29-Aug-03 4:33 
AnswerRe: Ditching.NET serialization in favor of MFC PinmemberGordon Brandly31-Aug-05 6:48 
GeneralProblem reading file PinmemberCount Zer021-Jul-03 9:19 
GeneralRe: Problem reading file PinsussAnonymous16-Jan-04 5:43 
Questionlibrary for XML serialization in C++ ? PinsussAnonymous17-Mar-03 1:15 
AnswerRe: library for XML serialization in C++ ? PinmemberRavi Bhavnani17-Mar-03 1:30 
AnswerRe: library for XML serialization in C++ ? PinmemberRodrigo Pinho Pereira de Souza16-Aug-05 3:22 
GeneralNewbie Question using CStdioFile PinmemberGregggggg23-Jan-03 16:55 
GeneralRe: Newbie Question using CStdioFile PinmemberRavi Bhavnani4-Mar-03 4:44 
GeneralForget MFC CArchive/CFile... PinmemberTBiker13-Jan-03 18:38 
GeneralRe: Forget MFC CArchive/CFile... PinmemberZac Howland3-Feb-03 6:18 
GeneralA General question about Serialization PinmemberNaresh25_cool23-Dec-02 1:19 
GeneralRe: A General question about Serialization PinsussAnonymous24-Dec-02 22:12 
GeneralRe: A General question about Serialization PinmemberRavi Bhavnani28-Dec-02 4:16 
GeneralRe: A General question about Serialization PinmemberZac Howland3-Feb-03 6:20 
GeneralA word of warning PinsussAnonymous18-Dec-02 21:51 
GeneralMore warnings... PinmemberPeter Weyzen8-Jan-03 11:14 
GeneralThis is good. PinmemberMarc Clifton15-Dec-02 13:58 
GeneralSerializing Multiple Object Types To Same File PinmemberMangesh Sardesai4-Dec-02 21:01 
GeneralRe: Serializing Multiple Object Types To Same File PinmemberRavi Bhavnani5-Dec-02 1:14 
GeneralRe: Serializing Multiple Object Types To Same File PinmemberMangesh Sardesai5-Dec-02 2:23 
GeneralRe: Serializing Multiple Object Types To Same File PinmemberRavi Bhavnani5-Dec-02 5:14 
Generali like Pinmemberumeflying4-Dec-02 20:25 
GeneralCObject PinmemberKarstenK27-Nov-02 0:51 
GeneralRe: CObject PinmemberRavi Bhavnani5-Dec-02 1:16 
GeneralRe: CObject PinmemberZac Howland3-Feb-03 6:24 
QuestionSmall bug? PinsussAnonymous13-Nov-02 8:24 
AnswerRe: Small bug? PinmemberRavi Bhavnani13-Nov-02 8:36 
GeneralRe: Small bug? PineditorBrian Delahunty26-Nov-02 7:53 
Generalcode Pinmembernewbie200219-Aug-02 23:59 
GeneralRe: code PinmemberRavi Bhavnani20-Aug-02 4:27 
GeneralSlight Bug PinmemberAnonymous5-Jun-02 18:42 
GeneralRe: Slight Bug PinmemberRavi Bhavnani7-Jun-02 12:16 
GeneralProper examples would be nice PinmemberAnonymous13-May-02 23:23 

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