The OLESTREAM structure is defined in the header file, OLE.H. The lpvtbl member in the OLESTREAM structure points to a table of function pointers for the client application. This structure is initialized and maintained by the client application for OLECLI.DLL.
OLE.H defines the OLESTREAM data structure as follows:
typedef struct _OLESTREAM {
LPOLESTREAMVTBL lpvtbl;
} OLESTREAM;