COBOL Tutorial

COBOL REWIND Statement - Quick Reference

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Overview

The REWIND statement is used to reposition a file to its beginning, allowing you to read the file from the start again without closing and reopening it. It is primarily used with sequential files for efficient file repositioning.

Purpose and Usage

File repositioning - Move file pointer to beginning
Efficient processing - Avoid close/open overhead
Multiple passes - Process same file multiple times
Error recovery - Restart processing after errors
Sequential access - Optimize sequential file operations

File Positioning Concept

File: [Record1] [Record2] [Record3] [Record4] [Record5]

After READ: [Record1] [Record2] [Record3] [Record4] [Record5]

↑ (current position)

After REWIND: [Record1] [Record2] [Record3] [Record4] [Record5]

↑ (back to beginning)

REWIND moves the file pointer back to the first record.

Syntax

The REWIND statement has a simple syntax and can be used with various file types.

Basic Syntax

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* Basic REWIND syntax
REWIND file-name
 
* With error handling
REWIND file-name
    ON EXCEPTION
        PERFORM ERROR-HANDLING
END-REWIND
 
* Complete example
IDENTIFICATION DIVISION.
PROGRAM-ID. REWIND-EXAMPLE.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT INPUT-FILE ASSIGN TO "DATA.TXT"
        ORGANIZATION IS SEQUENTIAL.
 
DATA DIVISION.
FILE SECTION.
FD  INPUT-FILE.
01  INPUT-RECORD PIC X(80).
 
WORKING-STORAGE SECTION.
01  FILE-STATUS PIC XX.
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    OPEN INPUT INPUT-FILE
    * Process file first time
    PERFORM PROCESS-FILE
    * Rewind to beginning
    REWIND INPUT-FILE
    * Process file second time
    PERFORM PROCESS-FILE
    CLOSE INPUT-FILE
    STOP RUN.
 
PROCESS-FILE.
    READ INPUT-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    DISPLAY INPUT-RECORD
    GO TO PROCESS-FILE.

REWIND requires the file to be open and available for reading.

REWIND vs CLOSE/OPEN Comparison

Method	Performance	Use Case
REWIND	Fast	Reposition to beginning
CLOSE/OPEN	Slower	Change file attributes
START	Medium	Position to specific record

Practical Examples

These examples demonstrate how to use the REWIND statement effectively in different file processing scenarios.

Multiple Pass Processing

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IDENTIFICATION DIVISION.
PROGRAM-ID. MULTI-PASS-PROCESSING.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT DATA-FILE ASSIGN TO "CUSTOMERS.DAT"
        ORGANIZATION IS SEQUENTIAL.
 
DATA DIVISION.
FILE SECTION.
FD  DATA-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  RECORD-COUNT       PIC 9(6) VALUE ZERO.
01  TOTAL-BALANCE      PIC 9(10)V99 VALUE ZERO.
01  AVERAGE-BALANCE    PIC 9(8)V99.
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    OPEN INPUT DATA-FILE
    
    * First pass: Count records and sum balances
    PERFORM COUNT-AND-SUM
    
    * Calculate average
    IF RECORD-COUNT > 0
        DIVIDE TOTAL-BALANCE BY RECORD-COUNT
            GIVING AVERAGE-BALANCE
    END-IF
    
    * Rewind for second pass
    REWIND DATA-FILE
    
    * Second pass: Display records above average
    PERFORM DISPLAY-ABOVE-AVERAGE
    
    CLOSE DATA-FILE
    STOP RUN.
 
COUNT-AND-SUM.
    READ DATA-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    ADD 1 TO RECORD-COUNT
    ADD CUST-BALANCE TO TOTAL-BALANCE
    GO TO COUNT-AND-SUM.
 
DISPLAY-ABOVE-AVERAGE.
    READ DATA-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    IF CUST-BALANCE > AVERAGE-BALANCE
        DISPLAY "High Balance: " CUST-NAME " - " CUST-BALANCE
    END-IF
    GO TO DISPLAY-ABOVE-AVERAGE.

REWIND allows efficient multiple passes over the same file.

Error Recovery

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* Error recovery with REWIND
PROCEDURE DIVISION.
PROCESS-WITH-RETRY.
    OPEN INPUT DATA-FILE
    PERFORM PROCESS-FILE
    CLOSE DATA-FILE.
 
PROCESS-FILE.
    READ DATA-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    
    * Simulate processing error
    IF CUST-BALANCE < 0
        DISPLAY "Error: Negative balance found"
        * Rewind and retry processing
        REWIND DATA-FILE
        PERFORM PROCESS-FILE
        EXIT PARAGRAPH
    END-IF
    
    * Normal processing
    DISPLAY "Processing: " CUST-NAME
    GO TO PROCESS-FILE.
 
* Alternative: Retry with different logic
PROCEDURE DIVISION.
RETRY-PROCESSING.
    OPEN INPUT DATA-FILE
    PERFORM FIRST-ATTEMPT
    * If first attempt fails, rewind and try different approach
    REWIND DATA-FILE
    PERFORM SECOND-ATTEMPT
    CLOSE DATA-FILE.
 
FIRST-ATTEMPT.
    READ DATA-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    * First processing logic
    GO TO FIRST-ATTEMPT.
 
SECOND-ATTEMPT.
    READ DATA-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    * Different processing logic
    GO TO SECOND-ATTEMPT.

REWIND enables error recovery by restarting file processing.

File Validation

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* File validation with multiple passes
WORKING-STORAGE SECTION.
01  VALIDATION-STATS.
    05  TOTAL-RECORDS    PIC 9(6) VALUE ZERO.
    05  VALID-RECORDS    PIC 9(6) VALUE ZERO.
    05  INVALID-RECORDS  PIC 9(6) VALUE ZERO.
    05  ERROR-MESSAGES   PIC X(100) OCCURS 10 TIMES.
 
PROCEDURE DIVISION.
VALIDATE-FILE.
    OPEN INPUT DATA-FILE
    
    * First pass: Count and validate
    PERFORM COUNT-AND-VALIDATE
    
    * Display validation results
    DISPLAY "Total Records: " TOTAL-RECORDS
    DISPLAY "Valid Records: " VALID-RECORDS
    DISPLAY "Invalid Records: " INVALID-RECORDS
    
    * Rewind for second pass: Process only valid records
    REWIND DATA-FILE
    
    * Second pass: Process valid records
    PERFORM PROCESS-VALID-RECORDS
    
    CLOSE DATA-FILE.
 
COUNT-AND-VALIDATE.
    READ DATA-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    ADD 1 TO TOTAL-RECORDS
    
    * Validation logic
    IF CUST-ID > 0 AND CUST-NAME NOT = SPACES
        ADD 1 TO VALID-RECORDS
    ELSE
        ADD 1 TO INVALID-RECORDS
        MOVE "Invalid record found" TO ERROR-MESSAGES(INVALID-RECORDS)
    END-IF
    GO TO COUNT-AND-VALIDATE.
 
PROCESS-VALID-RECORDS.
    READ DATA-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    
    * Only process if valid
    IF CUST-ID > 0 AND CUST-NAME NOT = SPACES
        DISPLAY "Processing valid record: " CUST-NAME
    END-IF
    GO TO PROCESS-VALID-RECORDS.

REWIND enables validation followed by processing of valid records.

Data Analysis

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* Data analysis with multiple passes
WORKING-STORAGE SECTION.
01  ANALYSIS-STATS.
    05  MIN-BALANCE      PIC 9(8)V99 VALUE 999999.99.
    05  MAX-BALANCE      PIC 9(8)V99 VALUE ZERO.
    05  MIN-CUSTOMER     PIC X(30).
    05  MAX-CUSTOMER     PIC X(30).
 
PROCEDURE DIVISION.
ANALYZE-DATA.
    OPEN INPUT DATA-FILE
    
    * First pass: Find min and max
    PERFORM FIND-MIN-MAX
    
    * Display analysis results
    DISPLAY "Minimum Balance: " MIN-BALANCE " - " MIN-CUSTOMER
    DISPLAY "Maximum Balance: " MAX-BALANCE " - " MAX-CUSTOMER
    
    * Rewind for second pass: Find records near min/max
    REWIND DATA-FILE
    
    * Second pass: Find similar records
    PERFORM FIND-SIMILAR-RECORDS
    
    CLOSE DATA-FILE.
 
FIND-MIN-MAX.
    READ DATA-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    
    IF CUST-BALANCE < MIN-BALANCE
        MOVE CUST-BALANCE TO MIN-BALANCE
        MOVE CUST-NAME TO MIN-CUSTOMER
    END-IF
    
    IF CUST-BALANCE > MAX-BALANCE
        MOVE CUST-BALANCE TO MAX-BALANCE
        MOVE CUST-NAME TO MAX-CUSTOMER
    END-IF
    GO TO FIND-MIN-MAX.
 
FIND-SIMILAR-RECORDS.
    READ DATA-FILE
        AT END
            EXIT PARAGRAPH
    END-READ
    
    * Find records within 10% of min or max
    IF CUST-BALANCE <= MIN-BALANCE * 1.10 OR
       CUST-BALANCE >= MAX-BALANCE * 0.90
        DISPLAY "Similar record: " CUST-NAME " - " CUST-BALANCE
    END-IF
    GO TO FIND-SIMILAR-RECORDS.

REWIND enables complex data analysis requiring multiple passes.

Best Practices and Considerations

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

Best Practices

Check file status - Always verify REWIND operations complete successfully
Ensure file is open - REWIND requires the file to be open
Use appropriate file mode - REWIND works with INPUT and I-O modes
Handle errors gracefully - Provide error recovery for REWIND failures
Consider performance - REWIND is more efficient than CLOSE/OPEN
Document usage - Clearly document when and why REWIND is used

File Organization Compatibility

File Organization	REWIND Support	Notes
Sequential	Yes	Primary use case
Relative	Yes	Repositions to record 1
Indexed	No	Use START instead
Line Sequential	Yes	Treats as sequential

Error Handling

File not open - Check file status before REWIND
Invalid file mode - Ensure file is opened for reading
File system errors - Handle system-level errors
Permission issues - Verify file access permissions
File corruption - Detect and handle file integrity issues

REWIND Statement Quick Reference

Usage	Syntax	Example
Basic REWIND	REWIND file-name	REWIND INPUT-FILE
With error handling	REWIND file-name ON EXCEPTION...	REWIND DATA-FILE ON EXCEPTION PERFORM ERROR-HANDLING
Multiple files	REWIND file1, file2	REWIND FILE1, FILE2
After processing	READ... REWIND... READ...	READ FILE AT END... REWIND FILE READ FILE...
Error recovery	IF error REWIND file	IF ERROR-FLAG = "Y" REWIND DATA-FILE

Test Your Knowledge

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

To delete a file
To reposition a file to its beginning
To create a new file
To close a file

2. Which file organization types support the REWIND statement?

Only indexed files
Only sequential files
Sequential and relative files
All file organization types

3. What happens when you REWIND a file that is not open?

The file is automatically opened
An error occurs
Nothing happens
The file is created

4. Can REWIND be used with files opened for OUTPUT?

Yes, always
No, never
Only if the file is empty
Only with certain file organizations

5. What is the relationship between REWIND and START statements?

They are the same thing
REWIND goes to beginning, START goes to specific position
REWIND is faster than START
They cannot be used together

Frequently Asked Questions

Related Concepts

File Processing

Understanding file processing operations in COBOL.

START Statement

Using START statement for file positioning.

READ Statement

Understanding READ operations for file access.

Sequential Files

Working with sequential file organization.

Error Handling

Error handling techniques in COBOL.

REVERSE-VIDEO REWRITE Statement

COBOL Tutorial

COBOL REWIND Statement - Quick Reference

Overview

Purpose and Usage

File Positioning Concept

Syntax

Basic Syntax

REWIND vs CLOSE/OPEN Comparison

Practical Examples

Multiple Pass Processing

Error Recovery

File Validation

Data Analysis

Best Practices and Considerations

Best Practices

File Organization Compatibility

Error Handling

REWIND Statement Quick Reference

Test Your Knowledge

Frequently Asked Questions

What is the difference between REWIND and CLOSE/OPEN for file repositioning?

How does REWIND affect the file status and error handling?

Can you use REWIND with indexed files?

What are some common use cases for the REWIND statement?

How do you handle errors when using the REWIND statement?

Related Concepts

File Processing

START Statement

READ Statement

Sequential Files

Error Handling

Related Pages