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COBOL Tutorial

COBOL EXCEPTION Handling

EXCEPTION handling represents a fundamental component of robust application development in COBOL, serving as the comprehensive framework for detecting, managing, and recovering from error conditions during program execution. This mechanism embodies defensive programming principles by providing systematic error detection capabilities, enabling sophisticated exception management processes, and supporting the development of resilient applications that can gracefully handle unexpected conditions while maintaining data integrity and operational continuity.

Comprehensive EXCEPTION Handling

cobol
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IDENTIFICATION DIVISION.
PROGRAM-ID. EXCEPTION-HANDLING-COMPREHENSIVE.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  EXCEPTION-MANAGEMENT-SYSTEM.
    05  EXCEPTION-STATUS        PIC X VALUE 'N'.
        88  EXCEPTION-OCCURRED  VALUE 'Y'.
        88  NO-EXCEPTION        VALUE 'N'.
    05  EXCEPTION-CODE          PIC 9(6) VALUE 0.
    05  EXCEPTION-MESSAGE       PIC X(100).
    05  EXCEPTION-SEVERITY      PIC X(8).
        88  SEVERITY-INFO       VALUE 'INFO'.
        88  SEVERITY-WARNING    VALUE 'WARNING'.
        88  SEVERITY-ERROR      VALUE 'ERROR'.
        88  SEVERITY-CRITICAL   VALUE 'CRITICAL'.
    05  EXCEPTION-TIMESTAMP     PIC X(14).
    05  EXCEPTION-LOCATION      PIC X(30).
 
01  CALL-EXCEPTION-HANDLING.
    05  PROGRAM-NAME            PIC X(8) VALUE 'SUBPROG1'.
    05  CALL-STATUS             PIC X VALUE 'N'.
        88  CALL-SUCCESS        VALUE 'Y'.
        88  CALL-FAILED         VALUE 'N'.
    05  CALL-PARAMETERS.
        10  PARAM-INPUT         PIC X(20).
        10  PARAM-OUTPUT        PIC X(50).
        10  PARAM-RETURN-CODE   PIC 9(4).
 
01  FILE-EXCEPTION-HANDLING.
    05  FILE-STATUS-CODE        PIC XX.
        88  FILE-SUCCESS        VALUE '00'.
        88  FILE-EOF            VALUE '10'.
        88  FILE-NOT-FOUND      VALUE '35'.
        88  FILE-ACCESS-DENIED  VALUE '37'.
        88  FILE-DISK-FULL      VALUE '34'.
    05  FILE-OPERATION          PIC X(10).
    05  FILE-NAME               PIC X(30).
 
01  ARITHMETIC-EXCEPTION-HANDLING.
    05  ARITHMETIC-RESULT       PIC 9(9)V99.
    05  DIVIDEND                PIC 9(7)V99 VALUE 1000.00.
    05  DIVISOR                 PIC 9(5)V99 VALUE 0.
    05  CALCULATION-STATUS      PIC X VALUE 'N'.
        88  CALC-SUCCESS        VALUE 'Y'.
        88  CALC-ERROR          VALUE 'N'.
 
01  EXCEPTION-STATISTICS.
    05  TOTAL-EXCEPTIONS        PIC 9(7) VALUE 0.
    05  CALL-EXCEPTIONS         PIC 9(5) VALUE 0.
    05  FILE-EXCEPTIONS         PIC 9(5) VALUE 0.
    05  ARITHMETIC-EXCEPTIONS   PIC 9(5) VALUE 0.
    05  CUSTOM-EXCEPTIONS       PIC 9(5) VALUE 0.
    05  RECOVERED-EXCEPTIONS    PIC 9(5) VALUE 0.
    05  UNRECOVERED-EXCEPTIONS  PIC 9(5) VALUE 0.
 
PROCEDURE DIVISION.
MAIN-PROCESSING.
    PERFORM INITIALIZE-EXCEPTION-SYSTEM
    PERFORM DEMONSTRATE-CALL-EXCEPTION-HANDLING
    PERFORM DEMONSTRATE-FILE-EXCEPTION-HANDLING
    PERFORM DEMONSTRATE-ARITHMETIC-EXCEPTION-HANDLING
    PERFORM DEMONSTRATE-CUSTOM-EXCEPTION-HANDLING
    PERFORM DISPLAY-EXCEPTION-STATISTICS
    STOP RUN.
 
INITIALIZE-EXCEPTION-SYSTEM.
    DISPLAY 'Initializing comprehensive exception handling system...'
    
    SET NO-EXCEPTION TO TRUE
    MOVE 0 TO EXCEPTION-CODE
    MOVE SPACES TO EXCEPTION-MESSAGE
    SET SEVERITY-INFO TO TRUE
    MOVE FUNCTION CURRENT-DATE TO EXCEPTION-TIMESTAMP
    
    DISPLAY 'Exception handling system ready'.
 
DEMONSTRATE-CALL-EXCEPTION-HANDLING.
    DISPLAY 'Demonstrating CALL exception handling...'
    
    MOVE 'INPUT-DATA' TO PARAM-INPUT
    MOVE SPACES TO PARAM-OUTPUT
    MOVE 0 TO PARAM-RETURN-CODE
    
    CALL PROGRAM-NAME USING CALL-PARAMETERS
        ON EXCEPTION
            SET EXCEPTION-OCCURRED TO TRUE
            MOVE 1001 TO EXCEPTION-CODE
            STRING 'CALL exception for program: ' DELIMITED BY SIZE
                   PROGRAM-NAME DELIMITED BY SPACE
                   INTO EXCEPTION-MESSAGE
            END-STRING
            SET SEVERITY-ERROR TO TRUE
            MOVE 'CALL-EXCEPTION' TO EXCEPTION-LOCATION
            ADD 1 TO CALL-EXCEPTIONS
            PERFORM HANDLE-CALL-EXCEPTION
        NOT ON EXCEPTION
            SET CALL-SUCCESS TO TRUE
            DISPLAY 'CALL to ' PROGRAM-NAME ' completed successfully'
            DISPLAY 'Return code: ' PARAM-RETURN-CODE
            DISPLAY 'Output: ' PARAM-OUTPUT
    END-CALL.
 
HANDLE-CALL-EXCEPTION.
    DISPLAY 'Handling CALL exception...'
    PERFORM LOG-EXCEPTION
    
    EVALUATE EXCEPTION-CODE
        WHEN 1001
            DISPLAY 'Program not found - attempting alternative'
            PERFORM ATTEMPT-ALTERNATIVE-PROGRAM
        WHEN OTHER
            DISPLAY 'Unknown CALL exception'
            PERFORM ESCALATE-EXCEPTION
    END-EVALUATE.
 
ATTEMPT-ALTERNATIVE-PROGRAM.
    MOVE 'SUBPROG2' TO PROGRAM-NAME
    DISPLAY 'Attempting alternative program: ' PROGRAM-NAME
    
    CALL PROGRAM-NAME USING CALL-PARAMETERS
        ON EXCEPTION
            DISPLAY 'Alternative program also failed'
            ADD 1 TO UNRECOVERED-EXCEPTIONS
        NOT ON EXCEPTION
            DISPLAY 'Alternative program succeeded'
            ADD 1 TO RECOVERED-EXCEPTIONS
    END-CALL.
 
DEMONSTRATE-FILE-EXCEPTION-HANDLING.
    DISPLAY 'Demonstrating file exception handling...'
    
    MOVE 'NONEXIST.DAT' TO FILE-NAME
    MOVE 'OPEN' TO FILE-OPERATION
    
    *> Simulate file operation with exception handling
    MOVE '35' TO FILE-STATUS-CODE  *> File not found
    
    PERFORM PROCESS-FILE-EXCEPTION
    
    IF EXCEPTION-OCCURRED
        PERFORM HANDLE-FILE-EXCEPTION
    END-IF.
 
PROCESS-FILE-EXCEPTION.
    EVALUATE FILE-STATUS-CODE
        WHEN '00'
            SET NO-EXCEPTION TO TRUE
            DISPLAY 'File operation successful: ' FILE-OPERATION
        WHEN '35'
            SET EXCEPTION-OCCURRED TO TRUE
            MOVE 2001 TO EXCEPTION-CODE
            STRING 'File not found: ' DELIMITED BY SIZE
                   FILE-NAME DELIMITED BY SPACE
                   ' during ' DELIMITED BY SIZE
                   FILE-OPERATION DELIMITED BY SPACE
                   INTO EXCEPTION-MESSAGE
            END-STRING
            SET SEVERITY-ERROR TO TRUE
            MOVE 'FILE-OPERATION' TO EXCEPTION-LOCATION
            ADD 1 TO FILE-EXCEPTIONS
        WHEN '37'
            SET EXCEPTION-OCCURRED TO TRUE
            MOVE 2002 TO EXCEPTION-CODE
            STRING 'Access denied: ' DELIMITED BY SIZE
                   FILE-NAME DELIMITED BY SPACE
                   INTO EXCEPTION-MESSAGE
            END-STRING
            SET SEVERITY-ERROR TO TRUE
            MOVE 'FILE-OPERATION' TO EXCEPTION-LOCATION
            ADD 1 TO FILE-EXCEPTIONS
        WHEN '34'
            SET EXCEPTION-OCCURRED TO TRUE
            MOVE 2003 TO EXCEPTION-CODE
            MOVE 'Disk full during file operation' TO EXCEPTION-MESSAGE
            SET SEVERITY-CRITICAL TO TRUE
            MOVE 'FILE-OPERATION' TO EXCEPTION-LOCATION
            ADD 1 TO FILE-EXCEPTIONS
        WHEN OTHER
            SET EXCEPTION-OCCURRED TO TRUE
            MOVE 2999 TO EXCEPTION-CODE
            STRING 'Unknown file error: ' DELIMITED BY SIZE
                   FILE-STATUS-CODE DELIMITED BY SIZE
                   INTO EXCEPTION-MESSAGE
            END-STRING
            SET SEVERITY-ERROR TO TRUE
            MOVE 'FILE-OPERATION' TO EXCEPTION-LOCATION
            ADD 1 TO FILE-EXCEPTIONS
    END-EVALUATE.
 
HANDLE-FILE-EXCEPTION.
    DISPLAY 'Handling file exception...'
    PERFORM LOG-EXCEPTION
    
    EVALUATE EXCEPTION-CODE
        WHEN 2001
            DISPLAY 'Attempting to create missing file'
            PERFORM CREATE-MISSING-FILE
        WHEN 2002
            DISPLAY 'Checking alternative file locations'
            PERFORM CHECK-ALTERNATIVE-LOCATIONS
        WHEN 2003
            DISPLAY 'Critical disk space issue'
            PERFORM ESCALATE-EXCEPTION
        WHEN OTHER
            DISPLAY 'General file error recovery'
            PERFORM ATTEMPT-FILE-RECOVERY
    END-EVALUATE.
 
CREATE-MISSING-FILE.
    DISPLAY 'Creating missing file: ' FILE-NAME
    *> Implementation would create the file
    ADD 1 TO RECOVERED-EXCEPTIONS
    DISPLAY 'File created successfully'.
 
CHECK-ALTERNATIVE-LOCATIONS.
    DISPLAY 'Checking alternative file locations...'
    *> Implementation would check backup locations
    ADD 1 TO RECOVERED-EXCEPTIONS
    DISPLAY 'Alternative location found'.
 
ATTEMPT-FILE-RECOVERY.
    DISPLAY 'Attempting file recovery procedures...'
    *> Implementation would attempt recovery
    ADD 1 TO RECOVERED-EXCEPTIONS
    DISPLAY 'File recovery completed'.
 
DEMONSTRATE-ARITHMETIC-EXCEPTION-HANDLING.
    DISPLAY 'Demonstrating arithmetic exception handling...'
    
    PERFORM SAFE-DIVISION-WITH-EXCEPTION-HANDLING
    PERFORM SAFE-MULTIPLICATION-WITH-EXCEPTION-HANDLING.
 
SAFE-DIVISION-WITH-EXCEPTION-HANDLING.
    DISPLAY 'Performing safe division with exception handling...'
    
    COMPUTE ARITHMETIC-RESULT = DIVIDEND / DIVISOR
        ON SIZE ERROR
            SET EXCEPTION-OCCURRED TO TRUE
            MOVE 3001 TO EXCEPTION-CODE
            STRING 'Division error: ' DELIMITED BY SIZE
                   DIVIDEND DELIMITED BY SIZE
                   ' / ' DELIMITED BY SIZE
                   DIVISOR DELIMITED BY SIZE
                   INTO EXCEPTION-MESSAGE
            END-STRING
            SET SEVERITY-ERROR TO TRUE
            MOVE 'ARITHMETIC-OPERATION' TO EXCEPTION-LOCATION
            ADD 1 TO ARITHMETIC-EXCEPTIONS
            PERFORM HANDLE-ARITHMETIC-EXCEPTION
        NOT ON SIZE ERROR
            SET CALC-SUCCESS TO TRUE
            DISPLAY 'Division result: ' ARITHMETIC-RESULT
    END-COMPUTE.
 
SAFE-MULTIPLICATION-WITH-EXCEPTION-HANDLING.
    DISPLAY 'Performing safe multiplication with exception handling...'
    
    MOVE 999999 TO DIVIDEND
    MOVE 999999 TO DIVISOR
    
    COMPUTE ARITHMETIC-RESULT = DIVIDEND * DIVISOR
        ON SIZE ERROR
            SET EXCEPTION-OCCURRED TO TRUE
            MOVE 3002 TO EXCEPTION-CODE
            STRING 'Multiplication overflow: ' DELIMITED BY SIZE
                   DIVIDEND DELIMITED BY SIZE
                   ' * ' DELIMITED BY SIZE
                   DIVISOR DELIMITED BY SIZE
                   INTO EXCEPTION-MESSAGE
            END-STRING
            SET SEVERITY-WARNING TO TRUE
            MOVE 'ARITHMETIC-OPERATION' TO EXCEPTION-LOCATION
            ADD 1 TO ARITHMETIC-EXCEPTIONS
            PERFORM HANDLE-ARITHMETIC-EXCEPTION
        NOT ON SIZE ERROR
            SET CALC-SUCCESS TO TRUE
            DISPLAY 'Multiplication result: ' ARITHMETIC-RESULT
    END-COMPUTE.
 
HANDLE-ARITHMETIC-EXCEPTION.
    DISPLAY 'Handling arithmetic exception...'
    PERFORM LOG-EXCEPTION
    
    EVALUATE EXCEPTION-CODE
        WHEN 3001
            DISPLAY 'Division by zero - using default value'
            MOVE 0 TO ARITHMETIC-RESULT
            ADD 1 TO RECOVERED-EXCEPTIONS
        WHEN 3002
            DISPLAY 'Overflow - using maximum value'
            MOVE 999999999.99 TO ARITHMETIC-RESULT
            ADD 1 TO RECOVERED-EXCEPTIONS
        WHEN OTHER
            DISPLAY 'Unknown arithmetic error'
            ADD 1 TO UNRECOVERED-EXCEPTIONS
    END-EVALUATE.
 
DEMONSTRATE-CUSTOM-EXCEPTION-HANDLING.
    DISPLAY 'Demonstrating custom exception handling...'
    
    PERFORM VALIDATE-BUSINESS-RULES-WITH-EXCEPTIONS
    PERFORM HANDLE-CUSTOM-BUSINESS-EXCEPTIONS.
 
VALIDATE-BUSINESS-RULES-WITH-EXCEPTIONS.
    DISPLAY 'Validating business rules...'
    
    *> Simulate business rule validation
    SET EXCEPTION-OCCURRED TO TRUE
    MOVE 4001 TO EXCEPTION-CODE
    MOVE 'Business rule violation: Customer age exceeds maximum' 
         TO EXCEPTION-MESSAGE
    SET SEVERITY-WARNING TO TRUE
    MOVE 'BUSINESS-VALIDATION' TO EXCEPTION-LOCATION
    ADD 1 TO CUSTOM-EXCEPTIONS.
 
HANDLE-CUSTOM-BUSINESS-EXCEPTIONS.
    IF EXCEPTION-OCCURRED
        DISPLAY 'Handling custom business exception...'
        PERFORM LOG-EXCEPTION
        
        EVALUATE EXCEPTION-CODE
            WHEN 4001
                DISPLAY 'Applying business rule override'
                PERFORM APPLY-BUSINESS-OVERRIDE
            WHEN OTHER
                DISPLAY 'Unknown business exception'
                PERFORM ESCALATE-EXCEPTION
        END-EVALUATE
    END-IF.
 
APPLY-BUSINESS-OVERRIDE.
    DISPLAY 'Applying business rule override...'
    ADD 1 TO RECOVERED-EXCEPTIONS
    DISPLAY 'Business rule override applied successfully'.
 
LOG-EXCEPTION.
    ADD 1 TO TOTAL-EXCEPTIONS
    MOVE FUNCTION CURRENT-DATE TO EXCEPTION-TIMESTAMP
    
    DISPLAY 'Exception Logged:'
    DISPLAY 'Code: ' EXCEPTION-CODE
    DISPLAY 'Message: ' EXCEPTION-MESSAGE
    DISPLAY 'Severity: ' EXCEPTION-SEVERITY
    DISPLAY 'Location: ' EXCEPTION-LOCATION
    DISPLAY 'Timestamp: ' EXCEPTION-TIMESTAMP.
 
ESCALATE-EXCEPTION.
    DISPLAY 'Escalating exception to higher level...'
    ADD 1 TO UNRECOVERED-EXCEPTIONS
    
    IF SEVERITY-CRITICAL
        DISPLAY 'Critical exception - immediate attention required'
        *> Could trigger alerts, notifications, etc.
    END-IF.
 
DISPLAY-EXCEPTION-STATISTICS.
    DISPLAY 'Exception Handling Statistics:'
    DISPLAY '================================'
    DISPLAY 'Total exceptions: ' TOTAL-EXCEPTIONS
    DISPLAY 'CALL exceptions: ' CALL-EXCEPTIONS
    DISPLAY 'File exceptions: ' FILE-EXCEPTIONS
    DISPLAY 'Arithmetic exceptions: ' ARITHMETIC-EXCEPTIONS
    DISPLAY 'Custom exceptions: ' CUSTOM-EXCEPTIONS
    DISPLAY 'Recovered exceptions: ' RECOVERED-EXCEPTIONS
    DISPLAY 'Unrecovered exceptions: ' UNRECOVERED-EXCEPTIONS
    
    IF TOTAL-EXCEPTIONS > 0
        COMPUTE RECOVERED-EXCEPTIONS = 
            (RECOVERED-EXCEPTIONS / TOTAL-EXCEPTIONS) * 100
        DISPLAY 'Recovery rate: ' RECOVERED-EXCEPTIONS '%'
    END-IF.

Best Practices and FAQ

Exception Best Practices
  • • Always use ON EXCEPTION with CALL statements
  • • Check file status codes after I/O operations
  • • Implement ON SIZE ERROR for arithmetic
  • • Create comprehensive error logging
  • • Design recovery procedures
Recovery Strategies
  • • Implement alternative processing paths
  • • Use default values for missing data
  • • Create backup file locations
  • • Implement retry mechanisms
  • • Escalate critical exceptions