StgCreateDocfileOnILockBytes

A version of this page is also available for

Windows Embedded CE 6.0 R3

4/8/2010

This function creates and opens a new compound file storage object on top of a byte array object provided by the caller. The storage object supports the OLE-provided, compound-file implementation for the IStorage interface.

Syntax

WINOLEAPI StgCreateDocfileOnILockBytes( 
  ILockBytes* plkbyt, 
  DWORD grfMode, 
  DWORD reserved, 
  IStorage** ppstgOpen 
); 

Parameters

• plkbyt
  [in] Pointer to the ILockBytes interface on the underlying byte array object on which to create a compound file.

• grfMode
  [in] Specifies the access mode to use when opening the new compound file. For more information, see the STGM enumeration.

• reserved
  [in] Reserved for future use. Set to zero.

• ppstgOpen
  [out] Pointer to the location of the IStorage pointer on the new storage object.

Return Value

One of the values described in the following table is returned.

This function can also return any file system errors, or Win32 errors wrapped in an HRESULT, or ILockBytes interface error return values.

Remarks

The StgCreateDocfileOnILockBytes and StgOpenStorageOnILockBytes functions are not available for the non-desktop compatible implementation by means of CESYSGEN.

The StgCreateDocfileOnILockBytes function creates a storage object on top of a byte array object using the COM-provided, compound-file implementation of the IStorage interface. StgCreateDocfileOnILockBytes can be used to store a document in a relational database. The byte array that is indicated by the pLkbyt parameter, which points to the ILockBytes interface on the object is used for the underlying storage in place of a disk file.

Except for specifying a programmer-provided byte-array object, StgCreateDocfileOnILockBytes is similar to the StgCreateDocfile function.

The newly created compound file is opened according to the access modes in the grfMode parameter. For conversion purposes, the file is always considered to already exist. As a result, it is not useful to use the STGM_FAILIFTHERE value, because it always causes an error to be returned. However, STGM_CREATE and STGM_CONVERT are both still useful.

The ability to build a compound file on top of a byte array object is provided to support having the data,underneath an IStorage and IStream tree structure, live in a non-persistent space. Given this capability, there is nothing preventing a document that is stored in a file from using this facility. For example, a container might do this to minimize the impact on its file format caused by adopting COM. However, it is recommended that COM documents adopt the IStorage interface for their own outer-level storage. This has the following advantages:

• The storage structure of the document is the same as its storage structure when it is an embedded object. This reduces the number of cases the application needs to handle.
• One can write tools to access the OLE embeddings and links within the document without special knowledge of the document's file format. An example of such a tool is a copy utility that copies all the documents included in a container containing linked objects. A copy utility like this needs access to the contained links to determine the extent of files to be copied.
• The IStorage implementation addresses the problem of how to commit the changes to the file. An application using the ILockBytes interface must handle these issues itself.
• Future file systems will likely implement the IStorage and IStream interfaces as their native abstractions, rather than layer on top of a byte array as is done in compound files. Such a file system could be built so that documents using the IStorage interface as their outer level containment structure would get an automatic efficiency gain by having the layering flattened when files are saved on the new file system.

Passing into this function any invalid and, under some circumstances, NULL pointers results in unexpected termination of the application.

To determine whether the platform supports this function, see Determining Supported COM APIs.

Requirements

See Also

Reference

ILockBytes
IStorage
IStream
StgCreateDocfile