What is error handling in COBOL?

Error handling in COBOL involves detecting, managing, and recovering from errors that occur during program execution, ensuring programs continue to operate reliably even when unexpected conditions arise.

How do you handle errors in COBOL?

Errors in COBOL are handled using file status codes, exception handling routines, validation checks, and error recovery procedures to manage various error conditions gracefully.

What are file status codes in COBOL?

File status codes in COBOL are two-character codes that indicate the result of file operations, helping programs detect and respond to file-related errors and conditions.

How do you validate input data in COBOL?

Input data in COBOL is validated using numeric checks, range validation, format validation, and business rule validation to ensure data integrity and prevent processing errors.

What is error recovery in COBOL?

Error recovery in COBOL involves implementing procedures to handle errors gracefully, restore program state, and continue processing when possible, or terminate cleanly when necessary.

How do you implement robust error handling in COBOL?

Robust error handling in COBOL is implemented through comprehensive validation, proper error detection, graceful error recovery, and detailed error logging and reporting.

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COBOL Error Handling Concepts

Error handling in COBOL involves detecting, managing, and recovering from errors that occur during program execution. Effective error handling ensures programs continue to operate reliably even when unexpected conditions arise. Understanding error handling concepts is essential for building robust, production-ready COBOL applications that can handle various error conditions gracefully.

Understanding Error Handling

Error handling in COBOL encompasses all methods of detecting, managing, and recovering from errors including file errors, data validation errors, arithmetic errors, and system errors. Proper error handling prevents program crashes, ensures data integrity, and provides meaningful error messages. Different error handling techniques are appropriate for different types of errors and program requirements.

File Error Handling

1. File Status Codes

File status codes are two-character codes that indicate the result of file operations. These codes help programs detect and respond to file-related errors and conditions such as end-of-file, file not found, or permission errors.

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       DATA DIVISION.
       FILE SECTION.
       FD INPUT-FILE.
       01 INPUT-RECORD        PIC X(100).
       
       WORKING-STORAGE SECTION.
       01 FILE-CONTROLS.
           05 FILE-STATUS     PIC XX VALUE '00'.
               88 FILE-OK     VALUE '00'.
               88 FILE-EOF    VALUE '10'.
               88 FILE-ERROR  VALUE '23' '24' '30' '34' '35' '37' '38' '39'.
       
       PROCEDURE DIVISION.
       PROCESS-FILE.
           OPEN INPUT INPUT-FILE
           
           IF NOT FILE-OK
               DISPLAY 'ERROR: Cannot open input file. Status: ' FILE-STATUS
               PERFORM FILE-ERROR-HANDLING
               STOP RUN
           END-IF
           
           PERFORM UNTIL FILE-EOF
               READ INPUT-FILE
               IF FILE-OK
                   PERFORM PROCESS-RECORD
               ELSE
                   IF FILE-EOF
                       DISPLAY 'End of file reached'
                   ELSE
                       DISPLAY 'ERROR: File read error. Status: ' FILE-STATUS
                       PERFORM FILE-ERROR-HANDLING
                   END-IF
               END-IF
           END-PERFORM
           
           CLOSE INPUT-FILE

File status codes provide detailed information about file operations. Common codes include '00' for success, '10' for end-of-file, and various error codes for different failure conditions. Always check file status after file operations.

2. File Error Recovery

File error recovery involves implementing procedures to handle file errors gracefully, retry operations when appropriate, and provide fallback mechanisms for critical file operations.

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       PROCEDURE DIVISION.
       FILE-ERROR-HANDLING.
           DISPLAY 'Handling file error with status: ' FILE-STATUS
           
           EVALUATE FILE-STATUS
               WHEN '23'
                   DISPLAY 'File not found - attempting to create'
                   PERFORM CREATE-FILE-IF-NEEDED
               WHEN '24'
                   DISPLAY 'File locked - retrying in 5 seconds'
                   PERFORM WAIT-AND-RETRY
               WHEN '30'
                   DISPLAY 'Permission denied - checking access rights'
                   PERFORM CHECK-PERMISSIONS
               WHEN '34'
                   DISPLAY 'Disk full - attempting cleanup'
                   PERFORM CLEANUP-DISK-SPACE
               WHEN OTHER
                   DISPLAY 'Unrecoverable file error'
                   PERFORM TERMINATE-GRACEFULLY
           END-EVALUATE.
       
       WAIT-AND-RETRY.
           MOVE 5 TO WAIT-SECONDS
           PERFORM VARYING RETRY-COUNT FROM 1 BY 1
               UNTIL RETRY-COUNT > 3
               DISPLAY 'Retry attempt ' RETRY-COUNT
               PERFORM DELAY-OPERATION
               PERFORM ATTEMPT-FILE-OPERATION
               IF FILE-OK
                   EXIT PERFORM
               END-IF
           END-PERFORM

File error recovery provides specific handling for different error conditions. Retry mechanisms, fallback procedures, and graceful degradation help maintain program stability.

Data Validation

1. Input Validation

Input validation checks data for correctness, format compliance, and business rule adherence before processing. This prevents errors caused by invalid or malformed data.

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       PROCEDURE DIVISION.
       VALIDATE-INPUT-DATA.
           DISPLAY 'Validating input data'
           
           *> Check for numeric data
           IF INPUT-AMOUNT NOT NUMERIC
               DISPLAY 'ERROR: Amount must be numeric: ' INPUT-AMOUNT
               MOVE 'INVALID' TO VALIDATION-STATUS
               PERFORM INVALID-DATA-HANDLING
           END-IF
           
           *> Check range
           IF INPUT-AMOUNT < 0 OR INPUT-AMOUNT > 999999.99
               DISPLAY 'ERROR: Amount out of range: ' INPUT-AMOUNT
               MOVE 'INVALID' TO VALIDATION-STATUS
               PERFORM INVALID-DATA-HANDLING
           END-IF
           
           *> Check required fields
           IF INPUT-NAME = SPACES
               DISPLAY 'ERROR: Name is required'
               MOVE 'INVALID' TO VALIDATION-STATUS
               PERFORM INVALID-DATA-HANDLING
           END-IF
           
           *> Check format
           IF INPUT-DATE NOT = FUNCTION CURRENT-DATE(1:8)
               DISPLAY 'ERROR: Invalid date format: ' INPUT-DATE
               MOVE 'INVALID' TO VALIDATION-STATUS
               PERFORM INVALID-DATA-HANDLING
           END-IF
           
           MOVE 'VALID' TO VALIDATION-STATUS
           DISPLAY 'Input validation passed'

Input validation ensures data integrity by checking data types, ranges, formats, and business rules. Comprehensive validation prevents processing errors and maintains data quality.

2. Business Rule Validation

Business rule validation enforces specific business logic and constraints that must be satisfied for data to be considered valid for processing.

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       PROCEDURE DIVISION.
       VALIDATE-BUSINESS-RULES.
           DISPLAY 'Validating business rules'
           
           *> Check credit limit
           IF CUSTOMER-BALANCE + TRANSACTION-AMOUNT > CREDIT-LIMIT
               DISPLAY 'ERROR: Transaction exceeds credit limit'
               DISPLAY 'Balance: ' CUSTOMER-BALANCE
               DISPLAY 'Transaction: ' TRANSACTION-AMOUNT
               DISPLAY 'Credit Limit: ' CREDIT-LIMIT
               MOVE 'REJECTED' TO TRANSACTION-STATUS
               PERFORM BUSINESS-RULE-ERROR
           END-IF
           
           *> Check account status
           IF ACCOUNT-STATUS = 'CLOSED'
               DISPLAY 'ERROR: Cannot process transaction on closed account'
               MOVE 'REJECTED' TO TRANSACTION-STATUS
               PERFORM BUSINESS-RULE-ERROR
           END-IF
           
           *> Check transaction limits
           IF DAILY-TRANSACTION-COUNT >= MAX-DAILY-TRANSACTIONS
               DISPLAY 'ERROR: Daily transaction limit exceeded'
               MOVE 'REJECTED' TO TRANSACTION-STATUS
               PERFORM BUSINESS-RULE-ERROR
           END-IF
           
           MOVE 'APPROVED' TO TRANSACTION-STATUS
           DISPLAY 'Business rule validation passed'

Business rule validation enforces specific business constraints and logic. These rules ensure transactions comply with business policies and regulatory requirements.

Arithmetic Error Handling

1. Division by Zero

Division by zero errors occur when attempting to divide by zero. COBOL provides mechanisms to detect and handle these errors before they cause program termination.

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       PROCEDURE DIVISION.
       SAFE-DIVISION.
           DISPLAY 'Performing safe division'
           
           *> Check for division by zero
           IF DIVISOR = 0
               DISPLAY 'ERROR: Division by zero attempted'
               MOVE 0 TO RESULT
               MOVE 'ERROR' TO CALCULATION-STATUS
               PERFORM ARITHMETIC-ERROR-HANDLING
           ELSE
               DIVIDE DIVIDEND BY DIVISOR GIVING RESULT
               MOVE 'SUCCESS' TO CALCULATION-STATUS
               DISPLAY 'Division result: ' RESULT
           END-IF.
       
       ARITHMETIC-ERROR-HANDLING.
           DISPLAY 'Handling arithmetic error'
           MOVE 0 TO RESULT
           ADD 1 TO ERROR-COUNT
           DISPLAY 'Error count: ' ERROR-COUNT

Division by zero handling prevents program crashes by checking divisors before division operations. Always validate divisors and provide appropriate error handling.

2. Overflow Handling

Overflow handling manages situations where arithmetic operations produce results that exceed the capacity of the receiving field, preventing data corruption and program errors.

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       PROCEDURE DIVISION.
       SAFE-ARITHMETIC.
           DISPLAY 'Performing safe arithmetic'
           
           *> Check for potential overflow
           COMPUTE TEMP-RESULT = FIELD-1 + FIELD-2
           
           IF TEMP-RESULT > MAX-VALUE
               DISPLAY 'ERROR: Arithmetic overflow detected'
               DISPLAY 'Field 1: ' FIELD-1
               DISPLAY 'Field 2: ' FIELD-2
               DISPLAY 'Result would be: ' TEMP-RESULT
               DISPLAY 'Maximum allowed: ' MAX-VALUE
               MOVE MAX-VALUE TO RESULT
               MOVE 'OVERFLOW' TO CALCULATION-STATUS
               PERFORM OVERFLOW-HANDLING
           ELSE
               MOVE TEMP-RESULT TO RESULT
               MOVE 'SUCCESS' TO CALCULATION-STATUS
               DISPLAY 'Arithmetic result: ' RESULT
           END-IF.
       
       OVERFLOW-HANDLING.
           DISPLAY 'Handling arithmetic overflow'
           ADD 1 TO OVERFLOW-COUNT
           DISPLAY 'Overflow count: ' OVERFLOW-COUNT

Overflow handling prevents data corruption by checking results before assignment. Use temporary variables for calculations and validate results before moving to target fields.

Error Recovery Strategies

1. Graceful Degradation

Graceful degradation allows programs to continue operating with reduced functionality when errors occur, rather than terminating completely.

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       PROCEDURE DIVISION.
       GRACEFUL-DEGRADATION.
           DISPLAY 'Implementing graceful degradation'
           
           *> Try primary operation
           PERFORM PRIMARY-OPERATION
           
           IF OPERATION-STATUS = 'FAILED'
               DISPLAY 'Primary operation failed, trying fallback'
               PERFORM FALLBACK-OPERATION
               
               IF FALLBACK-STATUS = 'FAILED'
                   DISPLAY 'Fallback failed, using default values'
                   PERFORM USE-DEFAULTS
               END-IF
           END-IF
           
           DISPLAY 'Operation completed with status: ' FINAL-STATUS.
       
       USE-DEFAULTS.
           DISPLAY 'Using default values for degraded operation'
           MOVE 'DEFAULT' TO OPERATION-RESULT
           MOVE 'DEGRADED' TO FINAL-STATUS

Graceful degradation provides fallback mechanisms when primary operations fail. This approach maintains program functionality even when some features are unavailable.

2. Error Logging and Reporting

Error logging and reporting capture error information for analysis, debugging, and system monitoring. This helps identify patterns and improve system reliability.

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       PROCEDURE DIVISION.
       LOG-ERROR.
           DISPLAY 'Logging error information'
           
           *> Capture error details
           MOVE FUNCTION CURRENT-DATE TO ERROR-TIMESTAMP
           MOVE PROGRAM-NAME TO ERROR-PROGRAM
           MOVE ERROR-CODE TO ERROR-NUMBER
           MOVE ERROR-MESSAGE TO ERROR-DESCRIPTION
           
           *> Write to error log
           WRITE ERROR-LOG-RECORD
           
           *> Update error statistics
           ADD 1 TO ERROR-COUNT
           ADD 1 TO DAILY-ERROR-COUNT
           
           DISPLAY 'Error logged: ' ERROR-NUMBER ' - ' ERROR-DESCRIPTION
           DISPLAY 'Total errors today: ' DAILY-ERROR-COUNT.
       
       REPORT-ERRORS.
           DISPLAY 'Generating error report'
           DISPLAY 'Total errors: ' ERROR-COUNT
           DISPLAY 'Daily errors: ' DAILY-ERROR-COUNT
           DISPLAY 'Last error: ' ERROR-NUMBER ' - ' ERROR-DESCRIPTION

Error logging captures detailed error information including timestamps, program names, error codes, and descriptions. This information helps with debugging and system monitoring.

Best Practices for Error Handling

Validate Early: Check data validity as early as possible in processing
Check File Status: Always check file status codes after file operations
Handle All Cases: Provide handling for all possible error conditions
Log Errors: Log all errors with sufficient detail for debugging
Provide Recovery: Implement recovery procedures when possible
Test Error Conditions: Test error handling with various error scenarios

Common Error Handling Patterns

File Error Handling: Check file status codes and implement retry logic
Data Validation: Validate input data before processing
Arithmetic Error Handling: Check for division by zero and overflow
Business Rule Validation: Enforce business constraints and rules
Graceful Degradation: Provide fallback mechanisms for failed operations
Error Logging: Capture and log error information for analysis

COBOL Error Handling Concepts

Understanding Error Handling

File Error Handling

1. File Status Codes

2. File Error Recovery

Data Validation

1. Input Validation

2. Business Rule Validation

Arithmetic Error Handling

1. Division by Zero

2. Overflow Handling

Error Recovery Strategies

1. Graceful Degradation

2. Error Logging and Reporting

Best Practices for Error Handling

Common Error Handling Patterns

Exception Handling

Debugging

Input Validation

File Status

Robust Programming

Error Recovery