The File Communication Block (FCB)

All HLI commands start with the command name as the first argument in the call, followed by the File Communication Block (FCB) as the second argument. For example:

The FCB has a fixed layout of 200 bytes. The user program supplies some FCB parameters, such as a filename for the database, and HLI fills in the others, such as the status return code.

When running a program under SU, place the characters SU in FCB word 6, followed by two trailing blanks. Place whatever ddname you assigned the communication data set associated with the FOCUS Database Server in FCB words 9 and 10. These are the only changes needed to make your programs run under SU.

FCB Area Layout

FCB Words	Item	Meaning	Bytes Used
1-2	FN	Filename of a FOCUS database(or HLI control command)	8
3-5	FT	Reserved	8
6	SU	SU (SU followed by two blanks)	4
7-8	PROCNAME	Displayed on HLIPRINT	8
9-10	SINKID	Ddname of communication data set	8
11-12	-	Reserved	8
13-15	-	Reserved	12
16-17	BACKKEY	Address key of target segment	8
18	ECHO	ECHO or STAT	4
19-20	PASSCTL	File access password	8
21-22	NEWSEG	Name of highest new segment retrieved	8
23	SEGNUM	Segment number of NEWSEG (integer)	4
24	STATUS	Status return code (integer)	4
25	ERRORNUM	Detail error code (integer)	4
26-32	-	Reserved	28
33	SHOLENGTH	Length of one record returned	4
34	LENGTH	Length of work area returned	4
35-50	-	Reserved	64

Note that the HLI program can place information useful for debugging in words 7 and 8 of the FCB. This information is displayed on the HLIPRINT trace in the PROCNAME column.

Using Both Local and Centrally Controlled Databases

A single program can use a combination of centrally controlled databases and local FOCUS databases. Whenever the program is using the centrally controlled databases, the FCB must have the characters SU in word 6 and the communication data set ddname in words 9 and 10. Under HLI, each open file must have its own FCB.

Error Codes

After every HLI call is executed, a status code is placed in the File Communication Block (FCB) word 24, shared by the host program and HLI. A status code of 0 means that the command executed correctly. A status code of 1 means that the command executed correctly, but no more data of the type requested was available. All higher numbered status codes indicate error conditions, such as incorrect field names or missing parameters. A list of status codes is provided in HLI Status Codes Returned in FCB Word 24.

If you are modifying the database using the INP, CHA, and DEL commands, and another user is trying to modify the same segment instance at the same time, your transaction may be rejected because the transaction submitted by other user was accepted first (this process is explained in Introduction). If this happens, your FCB receives one of the following status codes:

784: You attempted to add a new segment instance. Your transaction was rejected because another user added the same segment instance first. (Analogous to FOCURRENT=1 in MODIFY/SU.)
786: You attempted to update or delete a segment instance. Your transaction was rejected because another user deleted the instance first. (Analogous to FOCURRENT=2 in MODIFY/SU.)
789: You attempted to update or delete a segment instance. Your transaction was rejected because another user updated the instance first. (Analogous to FOCURRENT=3 in MODIFY/SU.)

Note: Status code 802, detail error code 5, indicates the FOCUS Database Server terminated abnormally.