COBOL Tutorial

COBOL REWRITE Statement - Quick Reference

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Overview

The REWRITE statement is used to update existing records in a file. It replaces the content of the current record (established by a previous READ) with new data while maintaining the same record position in the file.

Purpose and Usage

Record updates - Modify existing records in files
Data maintenance - Update customer, inventory, or transaction data
Status changes - Modify record status or flags
Error correction - Fix data errors in existing records
Audit trails - Update audit information in records

Update Process Concept

1. READ record: [ID:001] [Name:John] [Balance:100]

2. Modify data: [ID:001] [Name:John] [Balance:150]

3. REWRITE record: [ID:001] [Name:John] [Balance:150]

Record position unchanged, content updated

REWRITE updates the current record while maintaining its position.

Syntax

The REWRITE statement follows a specific pattern and requires proper file setup.

Basic Syntax

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* Basic REWRITE syntax
REWRITE record-name FROM data-item
 
* With error handling
REWRITE record-name FROM data-item
    ON EXCEPTION
        PERFORM ERROR-HANDLING
END-REWRITE
 
* Complete example
IDENTIFICATION DIVISION.
PROGRAM-ID. REWRITE-EXAMPLE.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE ASSIGN TO "CUSTOMERS.DAT"
        ORGANIZATION IS SEQUENTIAL
        ACCESS MODE IS SEQUENTIAL.
 
DATA DIVISION.
FILE SECTION.
FD  CUSTOMER-FILE.
01  CUSTOMER-RECORD.
    05  CUST-ID        PIC 9(6).
    05  CUST-NAME      PIC X(30).
    05  CUST-BALANCE   PIC 9(8)V99.
 
WORKING-STORAGE SECTION.
01  UPDATED-RECORD.
    05  UPD-CUST-ID    PIC 9(6).
    05  UPD-CUST-NAME  PIC X(30).
    05  UPD-CUST-BALANCE PIC 9(8)V99.
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    OPEN I-O CUSTOMER-FILE
    READ CUSTOMER-FILE
        AT END
            DISPLAY "No records found"
            CLOSE CUSTOMER-FILE
            STOP RUN
    END-READ
    
    * Update the record
    MOVE CUSTOMER-RECORD TO UPDATED-RECORD
    ADD 50 TO UPD-CUST-BALANCE
    
    REWRITE CUSTOMER-RECORD FROM UPDATED-RECORD
    CLOSE CUSTOMER-FILE
    STOP RUN.

REWRITE requires a previous READ and proper file mode (I-O).

REWRITE vs WRITE Comparison

Statement	Purpose	Requirement
REWRITE	Update existing record	Previous READ required
WRITE	Create new record	No READ required
DELETE	Remove record	Previous READ required

Practical Examples

These examples demonstrate how to use the REWRITE statement effectively in different update scenarios.

Customer Balance Update

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IDENTIFICATION DIVISION.
PROGRAM-ID. UPDATE-CUSTOMER-BALANCE.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE ASSIGN TO "CUSTOMERS.DAT"
        ORGANIZATION IS SEQUENTIAL.
 
DATA DIVISION.
FILE SECTION.
FD  CUSTOMER-FILE.
01  CUSTOMER-RECORD.
    05  CUST-ID        PIC 9(6).
    05  CUST-NAME      PIC X(30).
    05  CUST-BALANCE   PIC 9(8)V99.
    05  CUST-STATUS    PIC X(1).
 
WORKING-STORAGE SECTION.
01  SEARCH-ID          PIC 9(6).
01  UPDATE-AMOUNT      PIC 9(8)V99.
01  FOUND-FLAG         PIC X(1) VALUE "N".
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    DISPLAY "Enter customer ID to update: "
    ACCEPT SEARCH-ID
    DISPLAY "Enter amount to add: "
    ACCEPT UPDATE-AMOUNT
    
    OPEN I-O CUSTOMER-FILE
    
    PERFORM FIND-AND-UPDATE-CUSTOMER
    
    IF FOUND-FLAG = "N"
        DISPLAY "Customer not found"
    END-IF
    
    CLOSE CUSTOMER-FILE
    STOP RUN.
 
FIND-AND-UPDATE-CUSTOMER.
    READ CUSTOMER-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    
    IF CUST-ID = SEARCH-ID
        MOVE "Y" TO FOUND-FLAG
        ADD UPDATE-AMOUNT TO CUST-BALANCE
        
        * Update status if balance exceeds limit
        IF CUST-BALANCE > 10000
            MOVE "H" TO CUST-STATUS
        END-IF
        
        REWRITE CUSTOMER-RECORD
        DISPLAY "Customer updated successfully"
    ELSE
        GO TO FIND-AND-UPDATE-CUSTOMER
    END-IF.

REWRITE updates customer balance and status based on business rules.

Inventory Update

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* Inventory update with REWRITE
DATA DIVISION.
FILE SECTION.
FD  INVENTORY-FILE.
01  INVENTORY-RECORD.
    05  ITEM-CODE      PIC X(10).
    05  ITEM-DESC      PIC X(40).
    05  QUANTITY       PIC 9(6).
    05  REORDER-LEVEL  PIC 9(6).
    05  LAST-UPDATE    PIC X(8).
 
WORKING-STORAGE SECTION.
01  UPDATE-QUANTITY   PIC 9(6).
01  CURRENT-DATE      PIC X(8).
 
PROCEDURE DIVISION.
UPDATE-INVENTORY.
    MOVE FUNCTION CURRENT-DATE TO CURRENT-DATE
    
    OPEN I-O INVENTORY-FILE
    
    PERFORM UPDATE-INVENTORY-LOOP
    
    CLOSE INVENTORY-FILE.
 
UPDATE-INVENTORY-LOOP.
    READ INVENTORY-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    
    * Update quantity based on business logic
    IF QUANTITY < REORDER-LEVEL
        MOVE REORDER-LEVEL TO UPDATE-QUANTITY
        ADD 100 TO UPDATE-QUANTITY
        MOVE UPDATE-QUANTITY TO QUANTITY
        MOVE CURRENT-DATE TO LAST-UPDATE
        
        REWRITE INVENTORY-RECORD
        DISPLAY "Updated: " ITEM-CODE " - New Qty: " QUANTITY
    END-IF
    
    GO TO UPDATE-INVENTORY-LOOP.

REWRITE updates inventory quantities and timestamps automatically.

Transaction Status Update

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* Transaction status update
DATA DIVISION.
FILE SECTION.
FD  TRANSACTION-FILE.
01  TRANSACTION-RECORD.
    05  TRANS-ID       PIC 9(10).
    05  TRANS-AMOUNT   PIC 9(8)V99.
    05  TRANS-STATUS   PIC X(1).
    05  PROCESS-DATE   PIC X(8).
    05  ERROR-CODE     PIC X(3).
 
WORKING-STORAGE SECTION.
01  PROCESS-STATUS    PIC X(1) VALUE "P".
 
PROCEDURE DIVISION.
PROCESS-TRANSACTIONS.
    OPEN I-O TRANSACTION-FILE
    
    PERFORM PROCESS-TRANSACTION-LOOP
    
    CLOSE TRANSACTION-FILE.
 
PROCESS-TRANSACTION-LOOP.
    READ TRANSACTION-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    
    * Process based on status
    EVALUATE TRANS-STATUS
        WHEN "P"  * Pending
            PERFORM PROCESS-PENDING-TRANSACTION
        WHEN "E"  * Error
            PERFORM RETRY-ERROR-TRANSACTION
        WHEN "C"  * Complete
            CONTINUE
    END-EVALUATE
    
    GO TO PROCESS-TRANSACTION-LOOP.
 
PROCESS-PENDING-TRANSACTION.
    * Simulate processing
    IF TRANS-AMOUNT > 1000
        MOVE "E" TO TRANS-STATUS
        MOVE "001" TO ERROR-CODE
    ELSE
        MOVE "C" TO TRANS-STATUS
        MOVE FUNCTION CURRENT-DATE TO PROCESS-DATE
    END-IF
    
    REWRITE TRANSACTION-RECORD.
 
RETRY-ERROR-TRANSACTION.
    * Retry logic for error transactions
    IF ERROR-CODE = "001"
        MOVE "P" TO TRANS-STATUS
        MOVE SPACES TO ERROR-CODE
        REWRITE TRANSACTION-RECORD
    END-IF.

REWRITE updates transaction status and error codes during processing.

Data Correction

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* Data correction with validation
DATA DIVISION.
FILE SECTION.
FD  EMPLOYEE-FILE.
01  EMPLOYEE-RECORD.
    05  EMP-ID         PIC 9(6).
    05  EMP-NAME       PIC X(30).
    05  EMP-SALARY     PIC 9(8)V99.
    05  EMP-DEPT       PIC X(3).
    05  VALID-FLAG     PIC X(1).
 
WORKING-STORAGE SECTION.
01  CORRECTION-COUNT  PIC 9(3) VALUE ZERO.
 
PROCEDURE DIVISION.
CORRECT-EMPLOYEE-DATA.
    OPEN I-O EMPLOYEE-FILE
    
    PERFORM CORRECT-DATA-LOOP
    
    DISPLAY "Records corrected: " CORRECTION-COUNT
    CLOSE EMPLOYEE-FILE.
 
CORRECT-DATA-LOOP.
    READ EMPLOYEE-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    
    * Check for data issues and correct
    IF EMP-SALARY = ZERO
        MOVE 25000 TO EMP-SALARY
        MOVE "Y" TO VALID-FLAG
        REWRITE EMPLOYEE-RECORD
        ADD 1 TO CORRECTION-COUNT
        DISPLAY "Corrected salary for: " EMP-NAME
    END-IF
    
    IF EMP-DEPT = SPACES
        MOVE "GEN" TO EMP-DEPT
        MOVE "Y" TO VALID-FLAG
        REWRITE EMPLOYEE-RECORD
        ADD 1 TO CORRECTION-COUNT
        DISPLAY "Added department for: " EMP-NAME
    END-IF
    
    GO TO CORRECT-DATA-LOOP.

REWRITE corrects data errors and validates record integrity.

Best Practices and Considerations

Understanding best practices ensures reliable and efficient use of the REWRITE statement.

Best Practices

Always READ first - Ensure a current record exists before REWRITE
Validate data - Check data integrity before updating
Handle errors - Implement proper error handling for REWRITE operations
Use appropriate file mode - Open files in I-O mode for updates
Maintain audit trails - Log changes made through REWRITE
Test thoroughly - Verify REWRITE operations with various scenarios

File Organization Considerations

File Organization	REWRITE Behavior	Considerations
Sequential	Updates current record	Must read sequentially
Relative	Updates by record number	Can use READ with key
Indexed	Updates by key	Key must remain same

Error Handling

No current record - Check if READ was performed
File not open for update - Ensure I-O mode
Record locking - Handle concurrent access issues
File system errors - Check file status codes
Data validation errors - Validate before REWRITE

REWRITE Statement Quick Reference

Usage	Syntax	Example
Basic REWRITE	REWRITE record-name	REWRITE CUSTOMER-RECORD
With FROM clause	REWRITE record-name FROM data-item	REWRITE CUSTOMER-RECORD FROM UPDATED-DATA
With error handling	REWRITE record-name ON EXCEPTION...	REWRITE RECORD ON EXCEPTION PERFORM ERROR-HANDLING
After READ	READ... REWRITE...	READ FILE... REWRITE RECORD...
Conditional update	IF condition REWRITE record-name	IF VALID-DATA REWRITE CUSTOMER-RECORD

Test Your Knowledge

1. What is the primary purpose of the REWRITE statement in COBOL?

To create new records in a file
To update existing records in a file
To delete records from a file
To read records from a file

2. What must be done before using REWRITE?

The file must be opened for OUTPUT
A record must be read from the file
The file must be closed and reopened
The file must be created

3. Which file organization types support REWRITE?

Only sequential files
Only indexed files
Sequential, relative, and indexed files
Only relative files

4. What happens if you REWRITE without first reading a record?

The first record is updated
An error occurs
A new record is created
Nothing happens

5. How does REWRITE differ from WRITE?

REWRITE is faster than WRITE
REWRITE updates existing records, WRITE creates new records
REWRITE can only be used with indexed files
There is no difference

Frequently Asked Questions

Related Concepts

File Processing

Understanding file processing operations in COBOL.

READ Statement

Using READ statement to access file records.

WRITE Statement

Using WRITE statement to create new records.

DELETE Statement

Using DELETE statement to remove records.

Error Handling

Error handling techniques in COBOL.

REWIND Statement RIGHT Clause

COBOL Tutorial

COBOL REWRITE Statement - Quick Reference

Overview

Purpose and Usage

Update Process Concept

Syntax

Basic Syntax

REWRITE vs WRITE Comparison

Practical Examples

Customer Balance Update

Inventory Update

Transaction Status Update

Data Correction

Best Practices and Considerations

Best Practices

File Organization Considerations

Error Handling

REWRITE Statement Quick Reference

Test Your Knowledge

Frequently Asked Questions

What is the difference between REWRITE and WRITE statements?

How do you handle errors when using the REWRITE statement?

Can you use REWRITE with all file organization types?

What are some common use cases for the REWRITE statement?

How do you ensure data integrity when using REWRITE?

Related Concepts

File Processing

READ Statement

WRITE Statement

DELETE Statement

Error Handling

Related Pages