A 4-byte message-dependent reply parameter structure
C Declaration Method
Certain elements of information, placed into the parameters of a message, have data types that do not use all four bytes of this data type. The rules governing these cases are:
BOOL The value is contained in the low word and the high word is 0. SHORT The value is contained in the low word and its sign is extended into the high word. USHORT The value is contained in the low word and the high word is 0. NULL The entire four bytes are 0.
The structure of this data type depends on the message. For details, see the description of the particular message.