ILockBytes  1KKVJQN

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 an OLE 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 OLE provides implementations for the two most common situations:

File-based implementation   If you call StgCreateDocfileYN.O6Q 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   OLE 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 CreateILockBytesOnHGlobalNGR4FS function). Then, to create a compound file storage object on top of that byte array object, call the StgCreateDocfileOnILockBytes12AXX34 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 OLE-provided implementations. For a discussion of the advantages of using the OLE implementations rather than creating your own, see the StgCreateDocfileOnILockBytes12AXX34 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 IMarshal8SHYIG interface as part of your byte array object. The reason for this is that when the OLE-provided implementations of IStorage and IStream8MD3QE 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 OLE implementations of IStorageFS1VT1 and IStream8MD3QE 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 StgCreateDocfileOnILockBytes12AXX34 function to create a compound file storage object backed by your implementation of ILockBytes.

Methods in Vtable Order