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Structured Storage Class for ATL & MFC

, 20 Jul 2000
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A wrapper class for most common IStorage methods and API calls.
  • Download demo project - 12 Kb
  • Download source - 8 Kb
  • <!-- STEP 3. Add the article text.-->

    Structured storage is a useful tool in the software development. It allows us to open a single binary file and section it into several storages (which may be nested). Each storage may have one or more streams, which are used to write and retrieve the program specific information.

    All this functionality is built around COM objects that MS provides with the Windows OS. We access it via IStorage and IStream interfaces and a few API function calls. This, however, is a tedious job and I decided to write a thin wrapper around these interfaces and API calls.

    A Brief Example

    The following code snapshot shows the class in action ...
    StructuredStorage ss;
    //
    // Let's create a file. This also creates the root storage.
    //
    ss.CreateFile(L"SSTest.bin");
    //
    // Let's create a storage on the root one.
    //
    ss.CreateStorage(L"FirstLevel");
    //
    // Create a stream and write to it
    //
    CComPtr<IStream> spIStr;
    ss.CreateStream(&spIStr, L"A stream");
    CComBSTR bs(L"Some text to be written into the stream!");
    bs.WriteToStream(spIStr);
    //
    // ...
    

    Background Information

    At this point I must say that the structure of the class was inspired by the article and code of Andrew Peace. His solution suited me perfectly, but unfortunately, I find it useless (for my specific case, of course) due to following reasons:
    • Andrew's solution uses CString and CList and is therefore bound with MFC library. We need the structured storage functionality in a COM control and therefore the linkage to MFC is not desired.
    • A better look at his code shows that he uses several redundant variables, which complicate the code, unnecessarily.
    • Sometimes (though rarely) we need to know why an interface call or a function call failed.

    Although my solution eliminates the shortcomings above, it adds some new:

    • I am using a STL vector container. Some people try to avoid using STL containers in their COM objects.
    • If the solution is used inside a standard MFC project, a support for CComBSTR class is required (defined in "ATLBase.h"). Again, some people dislike this header in MFC code.
    • Advance features of structured storage management are still not provided.

    Implementation Information

    The class is build around a vector of IStorage objects. (IStorage object == storage, vector of storages == container) The first element of vector represents the root storage and subsequent elements represent sub storages. We can say that the vector of storages represents a path from the root storage to the last storage (the current one). Example:
    • [0] = root storage (level 0, not neceserally the root of the file).
    • [1] = storage inside the root (level 1).
    • [2] = storage inside the level 1 storage (level2)
    • [n] = current storage at level n (the last element of container).

    If the root storage is also the root of the structured file, say "C:\test\StructFile.bin", level 1 is "Level 1", level 2 is "Level 2", ... then the path to the current storage is:

    "C:\test\StructFile.bin|Level1|Level2|...|LevelN"

    Vertical char | is used to emphasize the borderline between the storages. Note, that the part of the path "Level1|Level2|...|LevelN" is hidden inside the "StructFile.bin" file.

    The front and the back of the vector are the most important storages. The former presents the root storage, while the later presents the current storage.

    Related Documentation

    Please refer to MSDN library and search for IStorage, IStream, StgCreateDocfile, StgOpenStorage, ... for more details.

    Final Remarks

    Those who look into the StructuredStorage.h file, will notice a lot of commented text and funny commands. They are required by the Doxygen documentation system. It is a free documentation utility that is able to generate HTML, HTML help, LaTeX, RTF, ... documents.

    I hope you will find the class useful!

    License

    This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

    A list of licenses authors might use can be found here

    About the Author

    Ales Krajnc
    Web Developer
    Slovenia Slovenia
    No Biography provided

    Comments and Discussions

     
    GeneralAlternative way for .NET PinmemberJan Gex23-Aug-06 4:48 
    QuestionHow to save HTMLs into single? PinmemberAlick Xiong16-Jun-04 21:06 
    GeneralFix for memory leak PinmemberPhil J Pearson26-Mar-04 5:57 
    GeneralRe: Fix for memory leak PinmemberPortatofe2-Oct-08 5:14 
    GeneralSTGM_SWMR PinmemberShashidhar Kamath26-Sep-03 6:58 
    GeneralSolution PinmemberShashidhar Kamath18-Sep-03 7:23 
    GeneralRe: Solution Pinmembermedhamp25-Sep-03 23:46 
    GeneralRe: Solution + Multi-Threads PinmemberKayuchkin Alexander12-Nov-03 19:58 
    Generalstructured file storage PinmemberShashidhar Kamath8-Apr-03 20:01 
    GeneralRe: structured file storage PinmemberMedhamp18-Sep-03 0:49 
    GeneralCloseFile method PinmemberSancho5-Jan-03 1:49 
    GeneralRe: CloseFile method PinmemberAles Krajnc5-Jan-03 6:06 
    GeneralRe: CloseFile method PinmemberAles Krajnc5-Jan-03 6:15 
    QuestionIStream ? Pinmemberswinefeaster11-May-02 17:02 
    AnswerRe: IStream ? PinsussHakan16-Aug-02 11:44 
    GeneralRe: IStream ? PinmemberSwinefeaster16-Aug-02 12:16 
    GeneralUNC paths PinmemberSerge Gommers22-Aug-01 9:59 

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