Structured Storage - The DocFile
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Feb 17, 2000
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A wrapper class for easy use of OLE structured storage.
Introduction
Structured storage is something which, when done using the plain Windows API, seems overly complicated; much more so than is needed. The aim of this article is to briefly introduce you to the concepts behind structured storage, and then provide a helper class to simplify its usage.
The idea behind structured storage is that a single file can itself contain a basic filing system. Its main reason for existence was to help with OLE documents: embedded objects are simply save as separate 'streams' within the single file. Here is a diagram which illustrates this concept:
| STRUCTURED STORAGE FILE |
|
Although this technology is primarily for use in OLE, it can be put to other uses. In order to help you access the functionality of this powerful tool easily, I have created a helper class, namely CSSFile, to aid in the creation, and modification of structured storage files.
Updates
If you have used this class previously, you will most likely wish to update your code to use the latest version. Here are the main differences (note that the interface remains the same):
- The use of const references for faster parameter passing
- Quicker operation as a result of reduced 'waste' code
- Removal of un-needed variables and code from the class
- Better arrangement of source and header files.
- Integration of help into the article rather than as a HTML Help download.
- Proper UNICODE awareness
Usage of the class
Whilst the class is fairly straightforward, I have listed the functions and their interfaces below to aid your usage of the class:
Function: CreateSSFile(...)
Parameters
filename - the name of the file to be created
mode - the mode of access for the file
Return value
'true' if the file was successfully created
Function: OpenSSFile(...)
Parameters
filename - the name of the file to open
mode - the mode of access for the file
Return value
'true' if the file was successfully opened
Function: Attach(...)
Parameters
pNews - the storage this object should hook
Return value
The previous storage being managed by the object
Function: Detach(...)
No Parameters
Return value
The previous storage being managed by the object
Function: Close()
No Parameters
No Return value
Function: CreateStorage(...)
Parameters
name - the name of the storage to create (will be created within the current path inside the root storage)
enter - enter the storage after creation?
mode - the mode of access for the storage
Return value
'true' if the storage was successfully created
Function: EnterStorage(...)
Parameters
name - the name of the storage to open
mode - the mode of access for the storage
Return value
'true' if the storage was successfully opened
Function: ExitStorage(...)
No Parameters
Return value
'true' if the storage path was moved up a level
Function: CreateStream(...)
Parameters
name - the name of the stream to create
sf - a COleStreamFile into which the stream is opened
mode - the mode of access for the stream
Return value
'true' if the stream was successfully created
Function: OpenStream(...)
Parameters
name - the name of the stream to open
sf - a COleStreamFile into which the stream is opened
mode - the mode of access for the stream
Return value
'true' if the stream was successfully opened
Function: DestroyElement(...)
Parameters
name - the name of the element to destroy
Return value
'true' if the element was successfully destroyed
Function: GetRootStorage()
No Parameters
Return value
The root of the currently open storage
Function: GetCurrentStorage()
No Parameters
Return value
The currently open storage
Function: IsOpen()
No Parameters
Return value
Whether a file is currently being managed by the object
Function: GetFilename()
No Parameters
Return value
The filename of the root storage
Function: GetPath(...)
Parameters
SepChar - the character to be used to separate the paths in the storages (i.e. Windows uses '\' for standard file system paths).
Return value
The current path within the storage (including the filename of the root storage).