IStream::Commit

Ensures that any changes made to a stream object open in transacted mode are reflected in the parent storage. If the stream object is open in direct mode, IStream::Commit has no effect other than flushing all memory buffers to the next level storage object. The OLE-provided implementation of streams does not support opening streams in transacted mode.

HRESULT Commit(

DWORD grfCommitFlags	//Specifies how changes are committed
);

Parameter
grfCommitFlags

[in]Controls how the changes for the stream object are committed. See the STGC enumeration for a definition of these values.

Return Values
S_OK

Changes to the stream object were successfully committed to the parent level.

STG_E_MEDIUMFULL

The commit operation failed due to lack of space on the storage device.

Comments
This method ensures that changes to a stream object opened in transacted mode are reflected in the parent storage. Changes that have been made to the stream since it was opened or last committed are reflected to the parent storage object. If the parent is opened in transacted mode, the parent may still revert at a later time rolling back the changes to this stream object.

If the stream is open in direct mode, this method ensures that any memory buffers have been flushed out to the underlying storage object. This is much like a flush in traditional file systems.

The IStream::Commit method is useful on a direct mode stream when the implementation of the IStream interface is a wrapper for underlying file system APIs. In this case, IStream::Commit would be connected to the file system's flush call.

Notes to Callers
The OLE-provided implementation of stream objects does not support transacted streams. Also, stream objects only exist within storage objects in this implementation. Thus, the OLE implementation of IStream::Commit has no effect other than flushing internal memory buffers to the parent storage object. With this implementation, it does not matter if you commit changes to streams. You can just commit changes for storage objects.