|
Enterprise COBOL for z/OS, Version 4.2, Programming Guide
Use the COBOL statements shown below to process VSAM files.
| COBOL statement |
Description |
| OPEN |
To connect the VSAM data set to your COBOL program for processing. |
| WRITE |
To add records to a file or load a file. |
| START |
To establish the current location in the cluster for a READ NEXT statement.
START does not retrieve a record; it only sets the current record pointer. |
| READ and READ NEXT |
To retrieve records from a file. |
| REWRITE |
To update records. |
| DELETE |
To logically remove records from indexed and relative files only. |
| CLOSE |
To disconnect the VSAM data set from your program. |
All of the following factors determine which input and output statements you can use for a given VSAM data set:
- Access mode (sequential, random, or dynamic)
- File organization (ESDS, KSDS, or RRDS)
- Mode of OPEN statement (INPUT, OUTPUT, I-O, or EXTEND)
The following table shows the possible combinations of statements and open modes for sequential files (ESDS).
The X indicates that you can use a statement with the open mode shown at the top of the column.
| Valid COBOL Statements with Sequential Files (ESDS) |
| Access mode |
COBOL statement |
OPEN INPUT |
OPEN OUTPUT |
OPEN I-O |
OPEN EXTEND |
| Sequential |
OPEN |
X |
X |
X |
X |
| WRITE |
|
X |
|
X |
| START |
|
|
|
|
| READ |
X |
|
X |
|
| REWRITE |
|
|
X |
|
| DELETE |
|
|
|
|
| CLOSE |
X |
X |
X |
X |
The following table shows the possible combinations of statements and open modes you can use with indexed (KSDS) files and relative (RRDS) files.
The X indicates that you can use the statement with the open mode shown at the top of the column.
| Valid COBOL Statements with Indexed Files (KSDS) and Relative Files (RRDS) |
| Access mode |
COBOL statement |
OPEN INPUT |
OPEN OUTPUT |
OPEN I-O |
OPEN EXTEND |
| Sequential |
OPEN |
X |
X |
X |
X |
| WRITE |
|
X |
|
X |
| START |
X |
|
X |
|
| READ |
X |
|
X |
|
| REWRITE |
|
|
X |
|
| DELETE |
|
|
X |
|
| CLOSE |
X |
X |
X |
X |
| Random |
OPEN |
X |
X |
X |
|
| WRITE |
|
X |
X |
|
| START |
|
|
|
|
| READ |
X |
|
X |
|
| REWRITE |
|
|
X |
|
| DELETE |
|
|
X |
|
| CLOSE |
X |
X |
X |
|
| Dynamic |
OPEN |
X |
X |
X |
|
| WRITE |
|
X |
X |
|
| START |
X |
|
X |
|
| READ |
X |
|
X |
|
| REWRITE |
|
|
X |
|
| DELETE |
|
|
X |
|
| CLOSE |
X |
X |
X |
|
The fields that you code in the FILE STATUS clause are updated by VSAM after each input-output statement to indicate the success or failure of the operation.
Related tasks
© Copyright tutorialspoint.com
|
