The OLECLIENT structure is defined in the header file, OLE.H. The lpvtbl member in the OLECLIENT 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 OLECLIENT data structure as follows:
typedef struct _OLECLIENT {
LPOLECLIENTVTBL lpvtbl;
} OLECLIENT;