Using Vsam In Cobol

Using VSAM in COBOL Changes in the ENVIRONMENT DIVISION: SELECT file-name ASSIGN TO ddname ORGANIZATION IS type ACCESS MODE IS access RECORD KEY IS key1 / RELATIVE KEY IS key2 FILE STATUS IS field1 [field2].

ddname

the ddname of the VSAM file being accessed

KSDS, RRDS format: DA-ddname ESDS format: DA-AS-ddname

type specifies the order that records have been stored in

SEQUENTIAL -- records are positioned in the order in which they were originally loaded (ESDS)

INDEXED -- records are positioned according to their index field (KSDS)

RELATIVE -- records are positioned according to their relative record number (RRDS)

access specifies how records are going to be processed

SEQUENTIAL -- read/write in sequential order

RANDOM -- read/write in a user specified order

DYNAMIC -- read/write in sequential, random, or both

key1 specifies the FD field name for the primary key field KSDS only value in the key must be unique

key2 field in working storage that a value will be moved to prior to a READ/WRITE RRDS only used with RANDOM or DYNAMIC access

field1 PIC XX field in working storage that will be used by COBOL to indicate the result of an OPEN, CLOSE, READ, or WRITE

00 success / non-zero failure

field2 6 byte return code that is supplied if field1 is not 00

01 VSAM-STATUS-CODES. 05 VSAM-RETURN-CODE

PIC 9(2) COMP.

05 VSAM-FUNCTION-CODE

PIC 9

COMP.

05 VSAM-FEEDBACK-CODE

PIC 9(3) COMP.

Changes in the DATA DIVISION: VSAM records are not labeled, therefore the LABEL RECORDS ARE... clause is treated as a comment, though it is required. VSAM records are not blocked, therefore the BLOCK CONTAINS... clause should not be specified.

Changes in the PROCEDURE DIVISION: Opening a file:

OPEN INPUT file-name. OUTPUT I-O EXTEND

I-O

file that will be read from and written to

EXTEND file that will have records added to the end

sequential file only

You can now test whether the files opened correct by testing the value placed in the FILE STATUS IS variable

Closing a file:

Same as before but you can now test if the close was successful

Reading from a file:

Cluster must be opened for INPUT or I-O

Sequential Read with Sequential Access:

READ file-name RECORD [INTO ws-field] AT END do something NOT AT END do something else END-READ.

Sequential Read with Dynamic Access:

READ file-name NEXT RECORD [INTO ws-field] AT END do something NOT AT END do something else END-READ.

Random Read with KSDS cluster:

MOVE value TO key1. READ file-name RECORD [INTO ws-field] INVALID KEY do something NOT INVALID KEY do something else END-READ.

Random Read with RRDS cluster:

MOVE value TO key2. READ file-name RECORD [INTO ws-field] INVALID KEY do something NOT INVALID KEY do something else END-READ.

Writing to a file:

Cluster must be opened for OUTPUT, I-O, or EXTEND

Sequential Write:

WRITE record_name [FROM ws-field].

Random Write for KSDS cluster:

MOVE value TO key1. WRITE record-name [FROM ws-field] INVALID KEY do something NOT INVALID KEY do something else END-WRITE.

Random Write for RRDS cluster:

MOVE value TO key2. WRITE record-name [FROM ws-field] INVALID KEY do something

NOT INVALID KEY do something else END-WRITE.

Rewriting a record to a file:

Cluster must be opened for I-O

Sequential Access:

Successful READ REWRITE record_name [FROM ws-field] INVALID KEY do something NOT INVALID KEY do something else END-REWRITE.

Rewrite for KSDS cluster:

MOVE value TO key1. REWRITE record-name [FROM ws-field] INVALID KEY do something NOT INVALID KEY do something else END-REWRITE.

Rewrite for RRDS cluster:

MOVE value TO key2. REWRITE record-name [FROM ws-field] INVALID KEY do something NOT INVALID KEY do something else END-REWRITE.

Deleting a record from a file:

Cluster must be opened for I-O

Sequential Access:

DELETE file-name RECORD.

Delete for KSDS cluster:

MOVE value TO key1. DELETE file-name RECORD INVALID KEY do something NOT INVALID KEY do something else

END-DELETE.

Delete for RRDS cluster:

MOVE value TO key2. DELETE file-name RECORD INVALID KEY do something NOT INVALID KEY do something else END-DELETE.

Records are logically deleted for RRDS

File OPENed for

File / Record

INVALID KEY

READ

INPUT, I-O

File

no such record

WRITE

OUTPUT, I-O, EXTEND

Record

duplicate key

REWRITE

I-O

Record

no such record

DELETE

I-O

File

no such record

The START statement Repositions the file pointer at a record other than the next logical record. File must be opened for INPUT or I-O START file-name KEY IS comparison key INVALID KEY do something NOT INVALID KEY do something else

END-START.

comparison the type of comparison to make between the records key field and the contents of key

EQUAL TO / = GREATER THAN / > NOT LESS THAN / NOT < GREATER THAN OR EQUAL TO / >=

key

relative or record key field

START does not actually read a record, it just repositions the file pointer.