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COBOL Tutorial

COBOL END-READ Statement

The END-READ statement represents a fundamental component of file processing operations in COBOL, serving as an explicit scope terminator that clearly defines the boundaries of READ statement blocks. This statement embodies modern file handling principles by providing unambiguous termination points for input operations, enabling sophisticated error handling for file access scenarios, and supporting the development of robust data processing applications that require precise control over file reading operations and exception management.

In contemporary enterprise COBOL development, END-READ plays a vital role in creating sophisticated file processing systems that must handle various file types, access methods, and error conditions. By providing explicit termination for READ blocks, this statement enables developers to implement comprehensive file processing logic while maintaining code clarity and ensuring that file operations are properly bounded and controlled within the application's data processing flow.

Basic END-READ Usage

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IDENTIFICATION DIVISION.
PROGRAM-ID. END-READ-DEMO.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT EMPLOYEE-FILE ASSIGN TO 'EMPLOYEES.DAT'
        ORGANIZATION IS SEQUENTIAL
        ACCESS MODE IS SEQUENTIAL
        FILE STATUS IS EMPLOYEE-FILE-STATUS.
    
    SELECT INDEXED-FILE ASSIGN TO 'INDEXED.DAT'
        ORGANIZATION IS INDEXED
        ACCESS MODE IS DYNAMIC
        RECORD KEY IS EMPLOYEE-ID
        FILE STATUS IS INDEXED-FILE-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  EMPLOYEE-FILE.
01  EMPLOYEE-RECORD.
    05  EMPLOYEE-ID             PIC X(10).
    05  EMPLOYEE-NAME           PIC X(30).
    05  EMPLOYEE-SALARY         PIC 9(7)V99.
    05  EMPLOYEE-DEPARTMENT     PIC X(15).
 
FD  INDEXED-FILE.
01  INDEXED-RECORD.
    05  EMPLOYEE-ID             PIC X(10).
    05  EMPLOYEE-DATA           PIC X(50).
 
WORKING-STORAGE SECTION.
01  FILE-STATUS-CODES.
    05  EMPLOYEE-FILE-STATUS    PIC XX.
        88  EMPLOYEE-FILE-OK    VALUE '00'.
        88  EMPLOYEE-FILE-EOF   VALUE '10'.
        88  EMPLOYEE-FILE-ERROR VALUE '01' THRU '09', '11' THRU '99'.
    
    05  INDEXED-FILE-STATUS     PIC XX.
        88  INDEXED-FILE-OK     VALUE '00'.
        88  INDEXED-FILE-EOF    VALUE '10'.
        88  INDEXED-FILE-ERROR  VALUE '01' THRU '09', '11' THRU '99'.
 
01  PROCESSING-COUNTERS.
    05  RECORDS-READ            PIC 9(7) VALUE 0.
    05  SUCCESSFUL-READS        PIC 9(7) VALUE 0.
    05  FAILED-READS            PIC 9(7) VALUE 0.
    05  EOF-REACHED             PIC X VALUE 'N'.
        88  END-OF-FILE         VALUE 'Y'.
 
01  SEARCH-CRITERIA.
    05  SEARCH-ID               PIC X(10).
    05  FOUND-FLAG              PIC X VALUE 'N'.
        88  RECORD-FOUND        VALUE 'Y'.
        88  RECORD-NOT-FOUND    VALUE 'N'.
 
PROCEDURE DIVISION.
MAIN-PROCESSING.
    PERFORM PROCESS-SEQUENTIAL-FILE
    PERFORM PROCESS-INDEXED-FILE
    PERFORM DISPLAY-STATISTICS
    STOP RUN.
 
PROCESS-SEQUENTIAL-FILE.
    DISPLAY 'Processing sequential file...'
    
    OPEN INPUT EMPLOYEE-FILE
    
    IF NOT EMPLOYEE-FILE-OK
        DISPLAY 'Error opening employee file: ' EMPLOYEE-FILE-STATUS
        STOP RUN
    END-IF
    
    PERFORM READ-SEQUENTIAL-RECORDS
    
    CLOSE EMPLOYEE-FILE
    
    DISPLAY 'Sequential file processing completed'.
 
READ-SEQUENTIAL-RECORDS.
    *> Read first record
    READ EMPLOYEE-FILE
        AT END
            DISPLAY 'File is empty'
            SET END-OF-FILE TO TRUE
        NOT AT END
            DISPLAY 'First record read successfully'
            ADD 1 TO RECORDS-READ
            ADD 1 TO SUCCESSFUL-READS
            PERFORM PROCESS-EMPLOYEE-RECORD
    END-READ
    
    *> Continue reading until end of file
    PERFORM UNTIL END-OF-FILE
        READ EMPLOYEE-FILE
            AT END
                DISPLAY 'End of file reached'
                SET END-OF-FILE TO TRUE
            NOT AT END
                ADD 1 TO RECORDS-READ
                
                *> Validate record before processing
                IF EMPLOYEE-ID NOT = SPACES AND EMPLOYEE-NAME NOT = SPACES
                    ADD 1 TO SUCCESSFUL-READS
                    PERFORM PROCESS-EMPLOYEE-RECORD
                ELSE
                    ADD 1 TO FAILED-READS
                    DISPLAY 'Invalid record found at position: ' RECORDS-READ
                END-IF
        END-READ
    END-PERFORM.
 
PROCESS-EMPLOYEE-RECORD.
    DISPLAY 'Processing employee: ' EMPLOYEE-ID
    DISPLAY 'Name: ' EMPLOYEE-NAME
    DISPLAY 'Salary: ' EMPLOYEE-SALARY
    DISPLAY 'Department: ' EMPLOYEE-DEPARTMENT
    DISPLAY '---'.
 
PROCESS-INDEXED-FILE.
    DISPLAY 'Processing indexed file...'
    
    OPEN I-O INDEXED-FILE
    
    IF NOT INDEXED-FILE-OK
        DISPLAY 'Error opening indexed file: ' INDEXED-FILE-STATUS
        STOP RUN
    END-IF
    
    PERFORM DEMONSTRATE-RANDOM-ACCESS
    PERFORM DEMONSTRATE-SEQUENTIAL-ACCESS
    
    CLOSE INDEXED-FILE
    
    DISPLAY 'Indexed file processing completed'.
 
DEMONSTRATE-RANDOM-ACCESS.
    DISPLAY 'Demonstrating random access reads:'
    
    *> Search for specific records
    MOVE 'EMP001' TO SEARCH-ID
    PERFORM SEARCH-INDEXED-RECORD
    
    MOVE 'EMP005' TO SEARCH-ID
    PERFORM SEARCH-INDEXED-RECORD
    
    MOVE 'EMP999' TO SEARCH-ID
    PERFORM SEARCH-INDEXED-RECORD.
 
SEARCH-INDEXED-RECORD.
    MOVE SEARCH-ID TO EMPLOYEE-ID
    SET RECORD-NOT-FOUND TO TRUE
    
    READ INDEXED-FILE
        KEY IS EMPLOYEE-ID
        INVALID KEY
            DISPLAY 'Record not found: ' SEARCH-ID
            SET RECORD-NOT-FOUND TO TRUE
        NOT INVALID KEY
            DISPLAY 'Record found: ' SEARCH-ID
            DISPLAY 'Data: ' EMPLOYEE-DATA
            SET RECORD-FOUND TO TRUE
    END-READ.
 
DEMONSTRATE-SEQUENTIAL-ACCESS.
    DISPLAY 'Demonstrating sequential access on indexed file:'
    
    *> Start from beginning
    MOVE LOW-VALUES TO EMPLOYEE-ID
    
    START INDEXED-FILE
        KEY IS GREATER THAN EMPLOYEE-ID
        INVALID KEY
            DISPLAY 'No records to process'
        NOT INVALID KEY
            PERFORM READ-INDEXED-SEQUENTIALLY
    END-START.
 
READ-INDEXED-SEQUENTIALLY.
    MOVE 'N' TO EOF-REACHED
    MOVE 0 TO RECORDS-READ
    
    PERFORM UNTIL END-OF-FILE OR RECORDS-READ >= 10
        READ INDEXED-FILE NEXT
            AT END
                DISPLAY 'End of indexed file reached'
                SET END-OF-FILE TO TRUE
            NOT AT END
                ADD 1 TO RECORDS-READ
                DISPLAY 'Sequential read #' RECORDS-READ
                DISPLAY 'ID: ' EMPLOYEE-ID
                DISPLAY 'Data: ' EMPLOYEE-DATA
        END-READ
    END-PERFORM.
 
DISPLAY-STATISTICS.
    DISPLAY 'File Processing Statistics:'
    DISPLAY 'Total records read: ' RECORDS-READ
    DISPLAY 'Successful reads: ' SUCCESSFUL-READS
    DISPLAY 'Failed reads: ' FAILED-READS
    
    IF RECORDS-READ > 0
        COMPUTE SUCCESSFUL-READS = 
            (SUCCESSFUL-READS / RECORDS-READ) * 100
        DISPLAY 'Success rate: ' SUCCESSFUL-READS '%'
    END-IF.

Advanced END-READ Patterns

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IDENTIFICATION DIVISION.
PROGRAM-ID. ADVANCED-END-READ.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT TRANSACTION-FILE ASSIGN TO 'TRANSACTIONS.DAT'
        ORGANIZATION IS SEQUENTIAL
        ACCESS MODE IS SEQUENTIAL
        FILE STATUS IS TRANS-FILE-STATUS.
    
    SELECT MASTER-FILE ASSIGN TO 'MASTER.DAT'
        ORGANIZATION IS INDEXED
        ACCESS MODE IS DYNAMIC
        RECORD KEY IS ACCOUNT-NUMBER
        ALTERNATE RECORD KEY IS CUSTOMER-NAME WITH DUPLICATES
        FILE STATUS IS MASTER-FILE-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  TRANSACTION-FILE.
01  TRANSACTION-RECORD.
    05  TRANS-TYPE              PIC X(2).
    05  ACCOUNT-NUMBER          PIC X(12).
    05  TRANS-AMOUNT            PIC 9(9)V99.
    05  TRANS-DATE              PIC X(8).
    05  TRANS-DESCRIPTION       PIC X(30).
 
FD  MASTER-FILE.
01  MASTER-RECORD.
    05  ACCOUNT-NUMBER          PIC X(12).
    05  CUSTOMER-NAME           PIC X(30).
    05  ACCOUNT-BALANCE         PIC S9(11)V99.
    05  ACCOUNT-STATUS          PIC X(2).
    05  LAST-ACTIVITY-DATE      PIC X(8).
 
WORKING-STORAGE SECTION.
01  FILE-STATUS-AREAS.
    05  TRANS-FILE-STATUS       PIC XX.
        88  TRANS-FILE-OK       VALUE '00'.
        88  TRANS-FILE-EOF      VALUE '10'.
        88  TRANS-FILE-ERROR    VALUE '01' THRU '09', '11' THRU '99'.
    
    05  MASTER-FILE-STATUS      PIC XX.
        88  MASTER-FILE-OK      VALUE '00'.
        88  MASTER-FILE-EOF     VALUE '10'.
        88  MASTER-RECORD-NOT-FOUND VALUE '23'.
        88  MASTER-FILE-ERROR   VALUE '01' THRU '09', '11' THRU '22', 
                                      '24' THRU '99'.
 
01  PROCESSING-CONTROLS.
    05  BATCH-SIZE              PIC 9(5) VALUE 1000.
    05  CURRENT-BATCH           PIC 9(5) VALUE 0.
    05  RECORDS-IN-BATCH        PIC 9(5) VALUE 0.
    05  TOTAL-PROCESSED         PIC 9(8) VALUE 0.
    05  VALIDATION-ERRORS       PIC 9(5) VALUE 0.
    05  UPDATE-ERRORS           PIC 9(5) VALUE 0.
 
01  TRANSACTION-VALIDATION.
    05  VALID-TRANS-TYPES       PIC X(10) VALUE 'DWCITF'.
    05  CURRENT-TRANS-TYPE      PIC X(2).
    05  VALIDATION-RESULT       PIC X VALUE 'N'.
        88  TRANSACTION-VALID   VALUE 'Y'.
        88  TRANSACTION-INVALID VALUE 'N'.
 
01  ERROR-HANDLING.
    05  ERROR-MESSAGE           PIC X(80).
    05  RETRY-COUNT             PIC 9(2) VALUE 0.
    05  MAX-RETRIES             PIC 9(2) VALUE 3.
    05  CONTINUE-PROCESSING     PIC X VALUE 'Y'.
        88  PROCESSING-ACTIVE   VALUE 'Y'.
        88  PROCESSING-STOPPED  VALUE 'N'.
 
PROCEDURE DIVISION.
MAIN-PROCESSING.
    PERFORM INITIALIZE-PROCESSING
    PERFORM PROCESS-TRANSACTION-BATCHES
    PERFORM FINALIZE-PROCESSING
    STOP RUN.
 
INITIALIZE-PROCESSING.
    DISPLAY 'Initializing transaction processing system...'
    
    OPEN INPUT TRANSACTION-FILE
    IF NOT TRANS-FILE-OK
        DISPLAY 'Fatal error opening transaction file: ' TRANS-FILE-STATUS
        STOP RUN
    END-IF
    
    OPEN I-O MASTER-FILE
    IF NOT MASTER-FILE-OK
        DISPLAY 'Fatal error opening master file: ' MASTER-FILE-STATUS
        CLOSE TRANSACTION-FILE
        STOP RUN
    END-IF
    
    DISPLAY 'Files opened successfully'
    DISPLAY 'Starting transaction processing...'.
 
PROCESS-TRANSACTION-BATCHES.
    SET PROCESSING-ACTIVE TO TRUE
    
    PERFORM UNTIL PROCESSING-STOPPED
        PERFORM PROCESS-SINGLE-BATCH
        
        *> Check if we should continue processing
        IF TRANS-FILE-EOF
            SET PROCESSING-STOPPED TO TRUE
            DISPLAY 'All transactions processed'
        ELSE
            IF VALIDATION-ERRORS > 100
                SET PROCESSING-STOPPED TO TRUE
                DISPLAY 'Too many validation errors - stopping'
            END-IF
        END-IF
    END-PERFORM.
 
PROCESS-SINGLE-BATCH.
    ADD 1 TO CURRENT-BATCH
    MOVE 0 TO RECORDS-IN-BATCH
    
    DISPLAY 'Processing batch: ' CURRENT-BATCH
    
    PERFORM UNTIL RECORDS-IN-BATCH >= BATCH-SIZE OR TRANS-FILE-EOF
        PERFORM READ-AND-VALIDATE-TRANSACTION
        
        IF TRANSACTION-VALID
            PERFORM PROCESS-VALID-TRANSACTION
        ELSE
            PERFORM HANDLE-INVALID-TRANSACTION
        END-IF
    END-PERFORM
    
    DISPLAY 'Batch ' CURRENT-BATCH ' completed'
    DISPLAY 'Records in batch: ' RECORDS-IN-BATCH
    DISPLAY 'Total processed: ' TOTAL-PROCESSED.
 
READ-AND-VALIDATE-TRANSACTION.
    MOVE 'N' TO VALIDATION-RESULT
    
    READ TRANSACTION-FILE
        AT END
            DISPLAY 'End of transaction file reached'
            SET TRANS-FILE-EOF TO TRUE
        NOT AT END
            ADD 1 TO RECORDS-IN-BATCH
            ADD 1 TO TOTAL-PROCESSED
            
            *> Validate transaction type
            MOVE TRANS-TYPE TO CURRENT-TRANS-TYPE
            IF CURRENT-TRANS-TYPE = 'DW' OR 'CR' OR 'IT' OR 'FT'
                *> Validate account number format
                IF ACCOUNT-NUMBER NOT = SPACES AND 
                   ACCOUNT-NUMBER NOT = LOW-VALUES
                    *> Validate amount
                    IF TRANS-AMOUNT > 0
                        SET TRANSACTION-VALID TO TRUE
                    ELSE
                        MOVE 'Invalid transaction amount' TO ERROR-MESSAGE
                    END-IF
                ELSE
                    MOVE 'Invalid account number' TO ERROR-MESSAGE
                END-IF
            ELSE
                MOVE 'Invalid transaction type' TO ERROR-MESSAGE
            END-IF
    END-READ.
 
PROCESS-VALID-TRANSACTION.
    *> Read corresponding master record
    MOVE ACCOUNT-NUMBER TO ACCOUNT-NUMBER OF MASTER-RECORD
    
    READ MASTER-FILE
        KEY IS ACCOUNT-NUMBER
        INVALID KEY
            DISPLAY 'Master record not found: ' ACCOUNT-NUMBER
            ADD 1 TO VALIDATION-ERRORS
            MOVE 'Account not found' TO ERROR-MESSAGE
            PERFORM LOG-TRANSACTION-ERROR
        NOT INVALID KEY
            PERFORM UPDATE-MASTER-RECORD
    END-READ.
 
UPDATE-MASTER-RECORD.
    EVALUATE TRANS-TYPE
        WHEN 'DW'  *> Debit/Withdrawal
            IF ACCOUNT-BALANCE >= TRANS-AMOUNT
                SUBTRACT TRANS-AMOUNT FROM ACCOUNT-BALANCE
                PERFORM REWRITE-MASTER-RECORD
            ELSE
                DISPLAY 'Insufficient funds for account: ' ACCOUNT-NUMBER
                ADD 1 TO UPDATE-ERRORS
            END-IF
        
        WHEN 'CR'  *> Credit/Deposit
            ADD TRANS-AMOUNT TO ACCOUNT-BALANCE
            PERFORM REWRITE-MASTER-RECORD
        
        WHEN 'IT'  *> Interest Transaction
            COMPUTE ACCOUNT-BALANCE = ACCOUNT-BALANCE + 
                   (ACCOUNT-BALANCE * (TRANS-AMOUNT / 10000))
            PERFORM REWRITE-MASTER-RECORD
        
        WHEN 'FT'  *> Fee Transaction
            SUBTRACT TRANS-AMOUNT FROM ACCOUNT-BALANCE
            PERFORM REWRITE-MASTER-RECORD
        
        WHEN OTHER
            DISPLAY 'Unhandled transaction type: ' TRANS-TYPE
            ADD 1 TO UPDATE-ERRORS
    END-EVALUATE.
 
REWRITE-MASTER-RECORD.
    MOVE TRANS-DATE TO LAST-ACTIVITY-DATE
    
    REWRITE MASTER-RECORD
        INVALID KEY
            DISPLAY 'Error updating master record: ' ACCOUNT-NUMBER
            DISPLAY 'File status: ' MASTER-FILE-STATUS
            ADD 1 TO UPDATE-ERRORS
        NOT INVALID KEY
            DISPLAY 'Account updated: ' ACCOUNT-NUMBER
            DISPLAY 'New balance: ' ACCOUNT-BALANCE
    END-REWRITE.
 
HANDLE-INVALID-TRANSACTION.
    ADD 1 TO VALIDATION-ERRORS
    DISPLAY 'Invalid transaction found:'
    DISPLAY 'Type: ' TRANS-TYPE
    DISPLAY 'Account: ' ACCOUNT-NUMBER
    DISPLAY 'Amount: ' TRANS-AMOUNT
    DISPLAY 'Error: ' ERROR-MESSAGE
    PERFORM LOG-TRANSACTION-ERROR.
 
LOG-TRANSACTION-ERROR.
    *> In a real system, this would write to an error log file
    DISPLAY 'ERROR LOG: ' ERROR-MESSAGE
    DISPLAY 'Transaction: ' TRANS-TYPE ' ' ACCOUNT-NUMBER ' ' TRANS-AMOUNT.
 
FINALIZE-PROCESSING.
    CLOSE TRANSACTION-FILE
    CLOSE MASTER-FILE
    
    DISPLAY 'Transaction processing completed'
    DISPLAY 'Statistics:'
    DISPLAY 'Total batches processed: ' CURRENT-BATCH
    DISPLAY 'Total transactions: ' TOTAL-PROCESSED
    DISPLAY 'Validation errors: ' VALIDATION-ERRORS
    DISPLAY 'Update errors: ' UPDATE-ERRORS
    
    IF TOTAL-PROCESSED > 0
        COMPUTE VALIDATION-ERRORS = 
            ((TOTAL-PROCESSED - VALIDATION-ERRORS - UPDATE-ERRORS) / 
             TOTAL-PROCESSED) * 100
        DISPLAY 'Success rate: ' VALIDATION-ERRORS '%'
    END-IF.

Best Practices and FAQ

Best Practices
  • • Always use END-READ with conditional processing
  • • Implement proper file status checking
  • • Handle both AT END and NOT AT END conditions
  • • Use meaningful error messages
  • • Validate data after reading
Common Mistakes
  • • Omitting END-READ in complex structures
  • • Not handling file status conditions
  • • Poor error handling implementation
  • • Missing data validation after reads
  • • Inefficient file access patterns