Summary -
In this topic, we described about the below sections -
REWRITE used to update the records that are already existed in the file. The REWRITE statement replaces an existing record with the new data in direct-access file.
The file must be opened in I-O mode for REWRITE statement. The REWRITE statement is not supported for line-sequential files.
Syntax -
record-name-1 -
Specifies the name of a logical record in a data division FD entry. The record-name can be qualified.
FROM phrase -
Specifies the data area that is not previously moved to record-name-1. FROM phrase avoids the explicit move of idetifier-1 to record-name-1. The FROM identifier-1 phrase is equivalent to the execution of the following statements -
MOVE identifier-1 to record-name-1. RELEASE record-name-1.
identifier-1 -
identifier-1 must reference one of the following -
- An entry in the working-storage section or the linkage section.
- A record description for another previously opened file.
- An alphanumeric function.
identifier-1 and record-name-1 should not refer to the same storage area. After the REWRITE statement is executed, the information is still available in identifier-1.
INVALID KEY phrase -
An INVALID KEY condition exists when -
- The access mode is sequential and the RECORD KEY value of the record to be replaced does not equal with the last-retrieved records RECORD KEY data item value from the file.
- The RECORD KEY value does not equal with the any record in the file.
- The ALTERNATE RECORD KEY data item value (DUPLICATES is not specified) is equal to the record that already in the file.
END-REWRITE phrase -
The END-REWRITE used to end the scope of the REWRITE statement. END-REWRITE is not required when REWRITE statement ended with period.
END-REWRITE can also be used with an imperative REWRITE statement. END-REWRITE permits conditional REWRITE to be nested in another conditional statement.
REWRITE on different file types -
If the FILE STATUS clause is specified, the associated file status key is updated when the REWRITE statement is executed.
Sequential files -
For files in the sequential access mode, the last prior input/output statement executed for this file must be a successfully executed READ statement.
When the REWRITE statement is executed, the record retrieved by that READ statement is logically replaced. The record-name-1 length must equal to the length of the record being replaced.
The INVALID KEY phrase must not be specified for a file with sequential organization. An EXCEPTION/ERROR procedure can be specified.
Indexed files -
The record-name-1 length can be different from the length of the record being replaced. The record to be replaced is identified by the RECORD KEY value. When the access mode is sequential -
- When the REWRITE statement is executed, the value must equal to the record key data item value that was from the last record read.
- Both the INVALID KEY phrase and an applicable EXCEPTION/ERROR procedure can be omitted.
When the access mode is random or dynamic -
- Values of ALTERNATE RECORD KEY data items in the rewritten record can differ from those in the record being replaced.
- If an INVALID KEY condition exists, the execution of the REWRITE statement is unsuccessful and the data in record-name-1 is unaffected.
Relative files -
The record-name-1 length can be different from the length of the record being replaced. When the access mode is sequential -
- The INVALID KEY phrase must not be specified and an EXCEPTION/ERROR procedure can be specified.
When the access mode is sequential -
- The INVALID KEY phrase or an applicable EXCEPTION/ERROR procedure can be specified. Both can be omitted.
When the access mode is random or dynamic -
- The record to be replaced is identified by RELATIVE KEY data item value.
- If the file does not contain the record specified, an INVALID KEY condition exists and the INVALID KEY imperative-statement is executed.
Practical Example -
Below example covers File REWRITE processing
Code:
IDENTIFICATION DIVISION.
PROGRAM-ID. FILEIO.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT FILE1 ASSIGN TO DISK1.
ORGANIZATION IS INDEXED.
ACCESS MODE IS RANDOM.
RECORD KEY IS STD-NO.
FILE STATUS IS WS-FS.
DATA DIVISION.
FILE SECTION.
FD FILE1.
RECORD CONTAINS 80 CHARACTERS.
BLOCK CONTAINS 800 CHARACTERS.
RECORDING MODE IS F.
DATA RECORD IS STD-REC.
01 STD-REC.
02 STD-NO PIC 9(03).
02 STD-NAME PIC X(20).
02 STD-GENDER PIC X(07).
02 FILLER PIC X(50).
WORKING-STORAGE SECTION.
77 WS-STD-NO PIC 9(03).
77 WS-STD-NAME PIC X(20).
77 WS-FS PIC 9(02).
01 WS-EOF-SW PIC X(01) VALUE 'N'.
88 EOF-SW VALUE 'Y'.
88 NOT-EOF-SW VALUE 'N'.
PROCEDURE DIVISION.
ACCEPT WS-STD-NO.
ACCEPT WS-STD-NAME.
MOVE WS-STD-NO TO STD-NO.
DISPLAY 'INDEXED FILE READING...'.
OPEN I-O FILE1.
READ FILE1
AT END MOVE 'Y' TO WS-EOF-SW.
IF WS-FS = 00
MOVE WS-STD-NAME TO STD-NAME
REWRITE STD-REC
ELSE
DISPLAY ' RECORD NOT FOUND IN FILE...'
END-IF.
CLOSE FILE1.
STOP RUN.