The ILockBytes interface is implemented on a byte array object that is backed by some physical storage, such as a disk file, global memory, or a database. It is used by a COM compound file storage object to give its root storage access to the physical device, while isolating the root storage from the details of accessing the physical storage.

When To Implement

Most applications will not implement the ILockBytes interface because COM provides implementations for the two most common situations:

• File-based implementation

  If you call StgCreateDocfile function to create a compound file storage object, it contains an implementation of ILockBytes that is associated with a byte array stored in a physical disk file. The compound file storage object calls the ILockBytes methods — you do not call them directly in this implementation.

• Memory-based implementation

  COM also provides a byte array object based on global memory that supports an implementation of ILockBytes. You can get a pointer through a call to the CreateILockBytesOnHGlobal function). Then, to create a compound file storage object on top of that byte array object, call the StgCreateDocfileOnILockBytes function. The compound file storage object calls the ILockBytes methods — you do not call them directly in this implementation.

There are situations in which it would be useful for an application to provide its own ILockBytes implementation. For example, a database application could implement ILockBytes to create a byte array object backed by the storage of its relational tables. However, it is strongly recommended that you use the COM-provided implementations. For a discussion of the advantages of using the COM implementations rather than creating your own, see the StgCreateDocfileOnILockBytes API function, which creates a compound file storage object on top of a caller-provided byte array object.

If you choose to implement your own ILockBytes interface, you should consider providing custom marshaling by implementing the IMarshal interface as part of your byte array object. The reason for this is that when the COM-provided implementations of IStorage and IStream are marshaled to another process, their ILockBytes interface pointers are also marshaled to the other process. The default marshaling mechanism creates a proxy byte array object (on which is the ILockBytes interface) that transmits method calls back to the original byte array object. Custom marshaling can improve efficiency by creating a remote byte array object that can access the byte array directly.

When To Use

The ILockBytes methods are called by the COM implementations of IStorage and IStream on the compound file object. Unless you are implementing IStorage and IStream, you would not need to call ILockBytes methods directly. If you write your own ILockBytes implementation, you can use the StgCreateDocfileOnILockBytes function to create a compound file storage object backed by your implementation of ILockBytes.

Methods

The ILockBytes interface inherits the methods of the IUnknown interface.

In addition, ILockBytes defines the following methods.

Requirements

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Build date: 11/12/2009