gtpd1m2e | Database Reference |
As previously mentioned, every class in TPFCS has the OBJECT class as its
base class; that is, all classes inherit from the OBJECT class.
For this reason, all objects are said to have an object header, which consists
of the attributes of OBJECT.
The object header contains the following data in the order presented:
- Object ID (class ID)
- A 4-byte field containing a hexadecimal value known as the class
ID of the object. The class ID stored in this field for a given
object represents its most detailed classification. This field is the
same attribute discussed in our previous abstract examples and identified an
object as being either a Limousine or a ClassC object, and so on. The
class IDs of all of the objects used by TPFCS are defined by CLASSID macro
statements in the ITO2 DSECT.
- Update sequence counter
- A 4-byte sequence counter field used by some application programming
interfaces (APIs).
- Object length
- A 4-byte field containing the length of the object when it is brought into
memory.
The value stored in this field will include the lengths of all attributes
inherited from higher classes, including the length of the object header
itself.
- spare
- An additional 4 bytes is reserved for future use by IBM.