COBOL Tutorial

COBOL Error Handling

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Introduction to Error Handling

Error handling is a critical aspect of COBOL programming that ensures programs operate reliably and gracefully handle unexpected situations. Proper error handling prevents program crashes, provides meaningful feedback, and enables recovery from error conditions.

Why Error Handling Matters

Effective error handling provides several benefits:

Program Reliability - Prevents unexpected program termination
Data Integrity - Ensures data remains consistent during errors
User Experience - Provides meaningful error messages and recovery options
Debugging - Helps identify and resolve issues quickly
Maintenance - Makes programs easier to maintain and modify
Audit Trail - Creates logs for tracking and analysis

Types of Errors in COBOL

COBOL programs can encounter various types of errors:

Error Type	Description	Examples
File Operation Errors	Errors related to file I/O operations	File not found, access denied, record not found
Data Validation Errors	Invalid or unexpected data values	Invalid input, overflow conditions, format errors
Arithmetic Errors	Mathematical operation failures	Division by zero, overflow, underflow
Logic Errors	Program flow and logic problems	Infinite loops, incorrect calculations, wrong paths
System Errors	Operating system and resource issues	Memory issues, resource conflicts, timeouts

File Status Codes

File status codes are two-character codes that provide detailed information about the result of file operations. They are essential for understanding what happened during file I/O operations and implementing appropriate error handling.

Understanding File Status Codes

File status codes are returned after file operations and indicate:

Success - Operation completed successfully
Normal Conditions - Expected conditions like end-of-file
Error Conditions - Problems that need to be handled
System Issues - Operating system or hardware problems

Each code has a specific meaning and requires appropriate handling.

Common File Status Codes

Status Code	Meaning	Action Required
"00"	Successful operation	Continue processing
"02"	Duplicate key (write operations)	Handle duplicate key
"04"	Record length error	Check record format
"10"	End of file	Normal end condition
"22"	Duplicate key (indexed files)	Handle duplicate key
"23"	Record not found	Handle missing record
"30"	Permanent error	Check file/system
"35"	File not found	Check file existence
"37"	File not open	Open file first
"39"	File conflict	Check file access

File Status Code Example

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* Example of checking file status codes
IDENTIFICATION DIVISION.
PROGRAM-ID. FILESTAT.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE ASSIGN TO "CUSTOMER.DAT"
        ORGANIZATION IS INDEXED
        ACCESS MODE IS RANDOM
        RECORD KEY IS CUSTOMER-ID
        FILE STATUS IS CUSTOMER-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  CUSTOMER-FILE
    LABEL RECORDS ARE STANDARD
    RECORD CONTAINS 80 CHARACTERS.
01  CUSTOMER-RECORD.
    05  CUSTOMER-ID       PIC 9(5).
    05  CUSTOMER-NAME     PIC X(30).
    05  CUSTOMER-ADDRESS  PIC X(35).
    05  CUSTOMER-BALANCE  PIC 9(7)V99.
 
WORKING-STORAGE SECTION.
01  CUSTOMER-STATUS       PIC XX.
01  SEARCH-ID             PIC 9(5).
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    PERFORM SEARCH-CUSTOMER
    PERFORM FINALIZATION
    STOP RUN.
 
INITIALIZATION.
    OPEN INPUT CUSTOMER-FILE
    EVALUATE CUSTOMER-STATUS
        WHEN "00"
            DISPLAY "File opened successfully"
        WHEN "35"
            DISPLAY "ERROR: File not found"
            STOP RUN
        WHEN "37"
            DISPLAY "ERROR: File not open"
            STOP RUN
        WHEN OTHER
            DISPLAY "ERROR: File open failed - Status: " CUSTOMER-STATUS
            STOP RUN
    END-EVALUATE.
 
SEARCH-CUSTOMER.
    DISPLAY "Enter customer ID to search: "
    ACCEPT SEARCH-ID
    
    MOVE SEARCH-ID TO CUSTOMER-ID
    READ CUSTOMER-FILE
        INVALID KEY
            PERFORM HANDLE-INVALID-KEY
        NOT INVALID KEY
            PERFORM HANDLE-SUCCESSFUL-READ
    END-READ.
 
HANDLE-INVALID-KEY.
    EVALUATE CUSTOMER-STATUS
        WHEN "23"
            DISPLAY "Customer " SEARCH-ID " not found"
        WHEN "30"
            DISPLAY "ERROR: Permanent file error"
        WHEN OTHER
            DISPLAY "ERROR: Read failed - Status: " CUSTOMER-STATUS
    END-EVALUATE.
 
HANDLE-SUCCESSFUL-READ.
    IF CUSTOMER-STATUS = "00"
        DISPLAY "Customer found:"
        DISPLAY "  ID: " CUSTOMER-ID
        DISPLAY "  Name: " CUSTOMER-NAME
        DISPLAY "  Address: " CUSTOMER-ADDRESS
        DISPLAY "  Balance: " CUSTOMER-BALANCE
    ELSE
        DISPLAY "WARNING: Unexpected status - " CUSTOMER-STATUS
    END-IF.
 
FINALIZATION.
    CLOSE CUSTOMER-FILE
    IF CUSTOMER-STATUS NOT = "00"
        DISPLAY "WARNING: File close error - Status: " CUSTOMER-STATUS
    END-IF.

This example shows comprehensive file status code checking at each step of file operations.

Error Handling Clauses

COBOL provides specific clauses for handling different types of error conditions. These clauses allow you to specify what action to take when certain conditions occur.

AT END Clause

The AT END clause is used with sequential file operations to handle the end-of-file condition when reading files.

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* AT END clause example
READ CUSTOMER-FILE
    AT END
        MOVE "Y" TO EOF-FLAG
        DISPLAY "End of file reached"
    NOT AT END
        PERFORM PROCESS-CUSTOMER
END-READ.
 
* Alternative AT END usage
READ TRANSACTION-FILE
    AT END
        PERFORM END-OF-FILE-PROCESSING
    NOT AT END
        IF TRANSACTION-STATUS = "00"
            PERFORM PROCESS-TRANSACTION
        ELSE
            PERFORM HANDLE-READ-ERROR
        END-IF
END-READ.

AT END is triggered when there are no more records to read from the file.

INVALID KEY Clause

The INVALID KEY clause is used with indexed and relative files for random access operations when key-related errors occur.

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* INVALID KEY clause example
MOVE SEARCH-ID TO CUSTOMER-ID
READ CUSTOMER-FILE
    INVALID KEY
        PERFORM HANDLE-INVALID-KEY
    NOT INVALID KEY
        PERFORM PROCESS-CUSTOMER
END-READ.
 
* INVALID KEY with status checking
MOVE NEW-CUSTOMER-ID TO CUSTOMER-ID
WRITE CUSTOMER-RECORD
    INVALID KEY
        EVALUATE CUSTOMER-STATUS
            WHEN "22"
                DISPLAY "Duplicate customer ID: " NEW-CUSTOMER-ID
            WHEN "23"
                DISPLAY "Record not found"
            WHEN OTHER
                DISPLAY "Write error - Status: " CUSTOMER-STATUS
        END-EVALUATE
    NOT INVALID KEY
        DISPLAY "Customer record written successfully"
END-WRITE.

INVALID KEY is triggered when a record with the specified key cannot be found or when there are duplicate key violations.

ON OVERFLOW Clause

The ON OVERFLOW clause is used with STRING operations to handle overflow conditions when the target field is too small.

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* ON OVERFLOW clause example
STRING FIRST-NAME DELIMITED BY SPACE,
       " " DELIMITED BY SIZE,
       LAST-NAME DELIMITED BY SIZE
       INTO FULL-NAME
       ON OVERFLOW
           PERFORM HANDLE-OVERFLOW
       NOT ON OVERFLOW
           DISPLAY "Name concatenated successfully"
END-STRING.
 
* ON OVERFLOW with error logging
STRING FIELD1 DELIMITED BY SIZE,
       FIELD2 DELIMITED BY SIZE,
       FIELD3 DELIMITED BY SIZE
       INTO TARGET-FIELD
       ON OVERFLOW
           MOVE "Y" TO OVERFLOW-FLAG
           DISPLAY "WARNING: String overflow occurred"
           DISPLAY "Target field size: " LENGTH OF TARGET-FIELD
       NOT ON OVERFLOW
           MOVE "N" TO OVERFLOW-FLAG
END-STRING.

ON OVERFLOW is triggered when a STRING operation would exceed the size of the target field.

ON SIZE ERROR Clause

The ON SIZE ERROR clause is used with arithmetic operations to handle overflow and underflow conditions.

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* ON SIZE ERROR clause example
COMPUTE RESULT = AMOUNT1 + AMOUNT2
    ON SIZE ERROR
        PERFORM HANDLE-ARITHMETIC-ERROR
    NOT ON SIZE ERROR
        PERFORM PROCESS-RESULT
END-COMPUTE.
 
* Division with ON SIZE ERROR
COMPUTE QUOTIENT = DIVIDEND / DIVISOR
    ON SIZE ERROR
        IF DIVISOR = ZERO
            DISPLAY "ERROR: Division by zero"
        ELSE
            DISPLAY "ERROR: Arithmetic overflow"
        END-IF
        MOVE ZERO TO QUOTIENT
    NOT ON SIZE ERROR
        DISPLAY "Division result: " QUOTIENT
END-COMPUTE.

ON SIZE ERROR is triggered when arithmetic operations result in overflow or underflow conditions.

Structured Error Handling

Structured error handling uses COBOL statements like EVALUATE to systematically check for different error conditions and handle them appropriately.

Using EVALUATE for Error Handling

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* Comprehensive error handling with EVALUATE
IDENTIFICATION DIVISION.
PROGRAM-ID. ERRORHANDLE.
 
WORKING-STORAGE SECTION.
01  FILE-STATUS       PIC XX.
01  ERROR-COUNT       PIC 9(3) VALUE ZERO.
01  SUCCESS-COUNT     PIC 9(3) VALUE ZERO.
01  OPERATION-TYPE    PIC X(10).
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM FILE-OPERATION
    PERFORM DISPLAY-STATISTICS
    STOP RUN.
 
FILE-OPERATION.
    MOVE "OPEN" TO OPERATION-TYPE
    OPEN INPUT CUSTOMER-FILE
    PERFORM CHECK-STATUS
    
    MOVE "READ" TO OPERATION-TYPE
    READ CUSTOMER-FILE
        AT END
            DISPLAY "End of file reached"
        NOT AT END
            PERFORM CHECK-STATUS
    END-READ
    
    MOVE "CLOSE" TO OPERATION-TYPE
    CLOSE CUSTOMER-FILE
    PERFORM CHECK-STATUS.
 
CHECK-STATUS.
    EVALUATE FILE-STATUS
        WHEN "00"
            ADD 1 TO SUCCESS-COUNT
            DISPLAY OPERATION-TYPE " operation successful"
        WHEN "10"
            DISPLAY "End of file (normal condition)"
        WHEN "23"
            ADD 1 TO ERROR-COUNT
            DISPLAY "ERROR: Record not found"
        WHEN "35"
            ADD 1 TO ERROR-COUNT
            DISPLAY "ERROR: File not found"
        WHEN "37"
            ADD 1 TO ERROR-COUNT
            DISPLAY "ERROR: File not open"
        WHEN "39"
            ADD 1 TO ERROR-COUNT
            DISPLAY "ERROR: File access conflict"
        WHEN "30"
            ADD 1 TO ERROR-COUNT
            DISPLAY "ERROR: Permanent file error"
        WHEN OTHER
            ADD 1 TO ERROR-COUNT
            DISPLAY "ERROR: Unknown status " FILE-STATUS
    END-EVALUATE.
 
DISPLAY-STATISTICS.
    DISPLAY "Operation Statistics:"
    DISPLAY "  Successful operations: " SUCCESS-COUNT
    DISPLAY "  Errors encountered: " ERROR-COUNT.

This example shows how to use EVALUATE for systematic error handling and statistics tracking.

Error Handling with Flags

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* Error handling using flags
WORKING-STORAGE SECTION.
01  ERROR-FLAGS.
    05  FILE-ERROR-FLAG     PIC X VALUE "N".
        88  FILE-ERROR       VALUE "Y".
    05  DATA-ERROR-FLAG     PIC X VALUE "N".
        88  DATA-ERROR       VALUE "Y".
    05  SYSTEM-ERROR-FLAG   PIC X VALUE "N".
        88  SYSTEM-ERROR     VALUE "Y".
01  ERROR-MESSAGE          PIC X(80).
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    IF NOT FILE-ERROR
        PERFORM PROCESS-DATA
    END-IF
    IF NOT DATA-ERROR
        PERFORM FINALIZATION
    END-IF
    PERFORM ERROR-REPORTING
    STOP RUN.
 
INITIALIZATION.
    OPEN INPUT CUSTOMER-FILE
    IF CUSTOMER-STATUS NOT = "00"
        MOVE "Y" TO FILE-ERROR-FLAG
        MOVE "File open failed" TO ERROR-MESSAGE
    END-IF.
 
PROCESS-DATA.
    PERFORM UNTIL FILE-ERROR OR DATA-ERROR
        READ CUSTOMER-FILE
            AT END
                EXIT PERFORM
            NOT AT END
                IF CUSTOMER-STATUS = "00"
                    PERFORM VALIDATE-CUSTOMER
                ELSE
                    MOVE "Y" TO FILE-ERROR-FLAG
                    MOVE "File read error" TO ERROR-MESSAGE
                END-IF
        END-READ
    END-PERFORM.
 
VALIDATE-CUSTOMER.
    IF CUSTOMER-ID = ZERO
        MOVE "Y" TO DATA-ERROR-FLAG
        MOVE "Invalid customer ID" TO ERROR-MESSAGE
    END-IF.
 
ERROR-REPORTING.
    IF FILE-ERROR OR DATA-ERROR OR SYSTEM-ERROR
        DISPLAY "ERROR REPORT:"
        IF FILE-ERROR
            DISPLAY "  File Error: " ERROR-MESSAGE
        END-IF
        IF DATA-ERROR
            DISPLAY "  Data Error: " ERROR-MESSAGE
        END-IF
        IF SYSTEM-ERROR
            DISPLAY "  System Error: " ERROR-MESSAGE
        END-IF
    ELSE
        DISPLAY "Program completed successfully"
    END-IF.

Using flags helps track different types of errors and control program flow.

Debugging Techniques

Effective debugging is essential for identifying and resolving errors in COBOL programs. Various techniques can help you trace program execution and identify problem areas.

Using DISPLAY for Debugging

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* Debugging with DISPLAY statements
IDENTIFICATION DIVISION.
PROGRAM-ID. DEBUGPROG.
 
WORKING-STORAGE SECTION.
01  DEBUG-FLAG           PIC X VALUE "N".
    88  DEBUG-MODE        VALUE "Y".
01  DEBUG-COUNTER        PIC 9(3) VALUE ZERO.
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    PERFORM PROCESS-DATA
    PERFORM FINALIZATION
    STOP RUN.
 
INITIALIZATION.
    IF DEBUG-MODE
        DISPLAY "DEBUG: Entering INITIALIZATION"
    END-IF
    
    OPEN INPUT CUSTOMER-FILE
    IF DEBUG-MODE
        DISPLAY "DEBUG: File open status: " CUSTOMER-STATUS
    END-IF.
 
PROCESS-DATA.
    PERFORM UNTIL END-OF-FILE
        READ CUSTOMER-FILE
            AT END
                MOVE "Y" TO EOF-FLAG
            NOT AT END
                IF DEBUG-MODE
                    ADD 1 TO DEBUG-COUNTER
                    DISPLAY "DEBUG: Processing record " DEBUG-COUNTER
                    DISPLAY "DEBUG: Customer ID: " CUSTOMER-ID
                END-IF
                PERFORM PROCESS-CUSTOMER
        END-READ
    END-PERFORM.
 
PROCESS-CUSTOMER.
    IF DEBUG-MODE
        DISPLAY "DEBUG: Customer balance: " CUSTOMER-BALANCE
    END-IF
    
    IF CUSTOMER-BALANCE > 1000
        IF DEBUG-MODE
            DISPLAY "DEBUG: High balance customer found"
        END-IF
        PERFORM PROCESS-HIGH-BALANCE
    END-IF.
 
FINALIZATION.
    IF DEBUG-MODE
        DISPLAY "DEBUG: Entering FINALIZATION"
        DISPLAY "DEBUG: Total records processed: " DEBUG-COUNTER
    END-IF
    CLOSE CUSTOMER-FILE.

DISPLAY statements can be used to trace program execution and output variable values for debugging.

Conditional Debugging

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* Conditional debugging with flags
WORKING-STORAGE SECTION.
01  DEBUG-CONTROLS.
    05  DEBUG-LEVEL       PIC 9 VALUE 1.
        88  DEBUG-BASIC    VALUE 1.
        88  DEBUG-DETAILED VALUE 2.
        88  DEBUG-VERBOSE  VALUE 3.
    05  DEBUG-FILE-FLAG   PIC X VALUE "N".
        88  DEBUG-FILE     VALUE "Y".
    05  DEBUG-DATA-FLAG   PIC X VALUE "N".
        88  DEBUG-DATA     VALUE "Y".
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    PERFORM PROCESS-DATA
    PERFORM FINALIZATION
    STOP RUN.
 
INITIALIZATION.
    IF DEBUG-BASIC
        DISPLAY "DEBUG: Program started"
    END-IF
    
    OPEN INPUT CUSTOMER-FILE
    IF DEBUG-FILE
        DISPLAY "DEBUG: File open status: " CUSTOMER-STATUS
    END-IF.
 
PROCESS-DATA.
    PERFORM UNTIL END-OF-FILE
        READ CUSTOMER-FILE
            AT END
                MOVE "Y" TO EOF-FLAG
            NOT AT END
                IF DEBUG-DETAILED
                    DISPLAY "DEBUG: Processing customer " CUSTOMER-ID
                END-IF
                PERFORM PROCESS-CUSTOMER
        END-READ
    END-PERFORM.
 
PROCESS-CUSTOMER.
    IF DEBUG-DATA
        DISPLAY "DEBUG: Customer data:"
        DISPLAY "  ID: " CUSTOMER-ID
        DISPLAY "  Name: " CUSTOMER-NAME
        DISPLAY "  Balance: " CUSTOMER-BALANCE
    END-IF
    
    IF DEBUG-VERBOSE
        DISPLAY "DEBUG: Performing calculations..."
    END-IF
    PERFORM CALCULATE-INTEREST.
 
FINALIZATION.
    IF DEBUG-BASIC
        DISPLAY "DEBUG: Program completed"
    END-IF.

Using debug flags allows you to control the level of debugging output without modifying the code.

Error Logging

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* Error logging and tracking
IDENTIFICATION DIVISION.
PROGRAM-ID. ERRORLOG.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT ERROR-LOG-FILE ASSIGN TO "ERROR.LOG"
        ORGANIZATION IS LINE SEQUENTIAL
        FILE STATUS IS LOG-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  ERROR-LOG-FILE
    LABEL RECORDS ARE STANDARD
    RECORD CONTAINS 100 CHARACTERS.
01  ERROR-LOG-RECORD.
    05  LOG-TIMESTAMP    PIC X(20).
    05  LOG-ERROR-CODE   PIC XX.
    05  LOG-ERROR-MSG    PIC X(60).
    05  LOG-PROGRAM-ID   PIC X(8).
 
WORKING-STORAGE SECTION.
01  LOG-STATUS          PIC XX.
01  CURRENT-TIME        PIC X(20).
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    PERFORM PROCESS-DATA
    PERFORM FINALIZATION
    STOP RUN.
 
INITIALIZATION.
    OPEN EXTEND ERROR-LOG-FILE
    IF LOG-STATUS NOT = "00"
        DISPLAY "WARNING: Cannot open error log file"
    END-IF.
 
LOG-ERROR.
    MOVE FUNCTION CURRENT-DATE TO CURRENT-TIME
    MOVE CURRENT-TIME TO LOG-TIMESTAMP
    MOVE FILE-STATUS TO LOG-ERROR-CODE
    MOVE ERROR-MESSAGE TO LOG-ERROR-MSG
    MOVE "ERRORLOG" TO LOG-PROGRAM-ID
    
    WRITE ERROR-LOG-RECORD
    IF LOG-STATUS NOT = "00"
        DISPLAY "WARNING: Error logging failed"
    END-IF.
 
PROCESS-DATA.
    OPEN INPUT CUSTOMER-FILE
    IF CUSTOMER-STATUS NOT = "00"
        MOVE "File open failed" TO ERROR-MESSAGE
        PERFORM LOG-ERROR
        STOP RUN
    END-IF
    
    PERFORM UNTIL END-OF-FILE
        READ CUSTOMER-FILE
            AT END
                MOVE "Y" TO EOF-FLAG
            NOT AT END
                IF CUSTOMER-STATUS NOT = "00"
                    MOVE "File read error" TO ERROR-MESSAGE
                    PERFORM LOG-ERROR
                ELSE
                    PERFORM PROCESS-CUSTOMER
                END-IF
        END-READ
    END-PERFORM.
 
FINALIZATION.
    CLOSE CUSTOMER-FILE
    CLOSE ERROR-LOG-FILE.

Error logging creates a permanent record of errors for analysis and debugging.

Data Validation and Error Prevention

Preventing errors through data validation is often more effective than handling them after they occur. COBOL provides various techniques for validating data before processing.

Input Validation

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* Comprehensive input validation
IDENTIFICATION DIVISION.
PROGRAM-ID. VALIDATE.
 
WORKING-STORAGE SECTION.
01  INPUT-DATA.
    05  CUSTOMER-ID       PIC 9(5).
    05  CUSTOMER-NAME     PIC X(30).
    05  CUSTOMER-AGE      PIC 9(3).
    05  CUSTOMER-SALARY   PIC 9(7)V99.
01  VALIDATION-FLAGS.
    05  ID-VALID          PIC X VALUE "N".
        88  VALID-ID       VALUE "Y".
    05  NAME-VALID        PIC X VALUE "N".
        88  VALID-NAME     VALUE "Y".
    05  AGE-VALID         PIC X VALUE "N".
        88  VALID-AGE      VALUE "Y".
    05  SALARY-VALID      PIC X VALUE "N".
        88  VALID-SALARY   VALUE "Y".
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM GET-INPUT
    PERFORM VALIDATE-INPUT
    IF VALID-ID AND VALID-NAME AND VALID-AGE AND VALID-SALARY
        PERFORM PROCESS-VALID-DATA
    ELSE
        PERFORM DISPLAY-VALIDATION-ERRORS
    END-IF
    STOP RUN.
 
GET-INPUT.
    DISPLAY "Enter Customer ID (5 digits): "
    ACCEPT CUSTOMER-ID
    DISPLAY "Enter Customer Name: "
    ACCEPT CUSTOMER-NAME
    DISPLAY "Enter Customer Age: "
    ACCEPT CUSTOMER-AGE
    DISPLAY "Enter Customer Salary: "
    ACCEPT CUSTOMER-SALARY.
 
VALIDATE-INPUT.
    PERFORM VALIDATE-CUSTOMER-ID
    PERFORM VALIDATE-CUSTOMER-NAME
    PERFORM VALIDATE-CUSTOMER-AGE
    PERFORM VALIDATE-CUSTOMER-SALARY.
 
VALIDATE-CUSTOMER-ID.
    IF CUSTOMER-ID > 0 AND CUSTOMER-ID <= 99999
        MOVE "Y" TO ID-VALID
    ELSE
        MOVE "N" TO ID-VALID
        DISPLAY "ERROR: Invalid Customer ID"
    END-IF.
 
VALIDATE-CUSTOMER-NAME.
    IF CUSTOMER-NAME NOT = SPACES AND 
       FUNCTION LENGTH(FUNCTION TRIM(CUSTOMER-NAME)) > 0
        MOVE "Y" TO NAME-VALID
    ELSE
        MOVE "N" TO NAME-VALID
        DISPLAY "ERROR: Customer name cannot be empty"
    END-IF.
 
VALIDATE-CUSTOMER-AGE.
    IF CUSTOMER-AGE >= 18 AND CUSTOMER-AGE <= 120
        MOVE "Y" TO AGE-VALID
    ELSE
        MOVE "N" TO AGE-VALID
        DISPLAY "ERROR: Age must be between 18 and 120"
    END-IF.
 
VALIDATE-CUSTOMER-SALARY.
    IF CUSTOMER-SALARY > 0 AND CUSTOMER-SALARY <= 9999999.99
        MOVE "Y" TO SALARY-VALID
    ELSE
        MOVE "N" TO SALARY-VALID
        DISPLAY "ERROR: Invalid salary amount"
    END-IF.
 
DISPLAY-VALIDATION-ERRORS.
    DISPLAY "VALIDATION ERRORS:"
    IF NOT VALID-ID
        DISPLAY "  - Invalid Customer ID"
    END-IF
    IF NOT VALID-NAME
        DISPLAY "  - Invalid Customer Name"
    END-IF
    IF NOT VALID-AGE
        DISPLAY "  - Invalid Age"
    END-IF
    IF NOT VALID-SALARY
        DISPLAY "  - Invalid Salary"
    END-IF.
 
PROCESS-VALID-DATA.
    DISPLAY "All data is valid - processing..."

Comprehensive input validation prevents invalid data from causing processing errors.

Range and Format Validation

cobol

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* Range and format validation examples
WORKING-STORAGE SECTION.
01  VALIDATION-RULES.
    05  MIN-AGE           PIC 9(3) VALUE 18.
    05  MAX-AGE           PIC 9(3) VALUE 120.
    05  MIN-SALARY        PIC 9(7)V99 VALUE 0.01.
    05  MAX-SALARY        PIC 9(7)V99 VALUE 9999999.99.
01  FORMAT-PATTERNS.
    05  VALID-EMAIL       PIC X(50) VALUE 
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789@._-".
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM VALIDATE-DATA
    STOP RUN.
 
VALIDATE-DATA.
    PERFORM VALIDATE-NUMERIC-RANGES
    PERFORM VALIDATE-STRING-FORMATS
    PERFORM VALIDATE-DATE-FORMATS.
 
VALIDATE-NUMERIC-RANGES.
    IF CUSTOMER-AGE < MIN-AGE OR CUSTOMER-AGE > MAX-AGE
        DISPLAY "ERROR: Age out of range (" MIN-AGE " to " MAX-AGE ")"
    END-IF
    
    IF CUSTOMER-SALARY < MIN-SALARY OR CUSTOMER-SALARY > MAX-SALARY
        DISPLAY "ERROR: Salary out of range"
    END-IF.
 
VALIDATE-STRING-FORMATS.
    * Check for valid characters in email
    INSPECT CUSTOMER-EMAIL
        TALLYING INVALID-CHAR-COUNT FOR ALL CHARACTERS
        NOT IN VALID-EMAIL
    END-INSPECT
    
    IF INVALID-CHAR-COUNT > 0
        DISPLAY "ERROR: Invalid characters in email address"
    END-IF.
 
VALIDATE-DATE-FORMATS.
    * Validate date format (MMDDYYYY)
    IF BIRTH-DATE(1:2) < "01" OR BIRTH-DATE(1:2) > "12"
        DISPLAY "ERROR: Invalid month in birth date"
    END-IF
    
    IF BIRTH-DATE(3:2) < "01" OR BIRTH-DATE(3:2) > "31"
        DISPLAY "ERROR: Invalid day in birth date"
    END-IF
    
    IF BIRTH-DATE(5:4) < "1900" OR BIRTH-DATE(5:4) > "2023"
        DISPLAY "ERROR: Invalid year in birth date"
    END-IF.

Range and format validation ensures data meets specific requirements before processing.

Best Practices and Guidelines

Following established best practices ensures robust error handling and maintainable COBOL programs.

Error Handling Best Practices

Always check file status codes after file operations
Use appropriate error handling clauses (AT END, INVALID KEY, ON OVERFLOW)
Implement comprehensive data validation before processing
Provide meaningful error messages that help users understand the problem
Log errors appropriately for debugging and audit purposes
Handle all possible error conditions gracefully
Use structured error handling with EVALUATE statements
Maintain error flags and counters for monitoring
Implement proper cleanup procedures in error situations
Test error conditions thoroughly during development

Debugging Best Practices

Use conditional debugging with flags that can be easily enabled/disabled
Add strategic DISPLAY statements at key program points
Implement comprehensive logging of program execution and errors
Use meaningful variable names for debugging output
Create debug versions of programs for troubleshooting
Document debugging procedures for future reference
Use different debug levels for different types of information
Remove or disable debug code in production versions

Data Validation Best Practices

Validate all input data before processing
Check data ranges and formats according to business rules
Use consistent validation patterns throughout the program
Provide clear validation error messages to users
Implement both client-side and server-side validation
Use validation flags to track multiple validation errors
Document validation rules for maintenance
Test validation with edge cases and boundary conditions

Common Pitfalls to Avoid

Ignoring file status codes after file operations
Not handling end-of-file conditions in sequential reads
Forgetting to check for division by zero in arithmetic operations
Not validating input data before processing
Using generic error messages that don't help with debugging
Not implementing proper cleanup in error situations
Leaving debug code in production programs
Not testing error conditions during development
Using inconsistent error handling patterns throughout the program
Not documenting error handling procedures for maintenance

Test Your Knowledge

1. What is the primary purpose of file status codes in COBOL?

To provide detailed information about the result of file operations
To indicate program compilation errors
To show system resource usage
To display user input validation errors

2. Which file status code indicates a successful operation?

"10"
"00"
"23"
"30"

3. What does the INVALID KEY clause handle in COBOL?

File open errors
Record not found or duplicate key conditions
Syntax errors
Memory allocation errors

4. Which statement is used for structured error handling in COBOL?

IF-THEN-ELSE
EVALUATE
PERFORM
MOVE

5. What is the purpose of the ON OVERFLOW clause in STRING operations?

To handle end-of-file conditions
To handle when the target field is too small for the concatenated result
To handle file open errors
To handle division by zero errors

COBOL Tutorial

COBOL Error Handling

Introduction to Error Handling

Why Error Handling Matters

Types of Errors in COBOL

File Status Codes

Understanding File Status Codes

Common File Status Codes

File Status Code Example

Error Handling Clauses

AT END Clause

INVALID KEY Clause

ON OVERFLOW Clause

ON SIZE ERROR Clause

Structured Error Handling

Using EVALUATE for Error Handling

Error Handling with Flags

Debugging Techniques

Using DISPLAY for Debugging

Conditional Debugging

Error Logging

Data Validation and Error Prevention

Input Validation

Range and Format Validation

Best Practices and Guidelines

Error Handling Best Practices

Debugging Best Practices

Data Validation Best Practices

Common Pitfalls to Avoid

Test Your Knowledge

Frequently Asked Questions

Related Concepts

File Status Error Handling

Data Validation

Debugging Techniques

Exception Handling

Program Structure

Related Pages

COBOL Tutorial

COBOL Error Handling

Introduction to Error Handling

Why Error Handling Matters

Types of Errors in COBOL

File Status Codes

Understanding File Status Codes

Common File Status Codes

File Status Code Example

Error Handling Clauses

AT END Clause

INVALID KEY Clause

ON OVERFLOW Clause

ON SIZE ERROR Clause

Structured Error Handling

Using EVALUATE for Error Handling

Error Handling with Flags

Debugging Techniques

Using DISPLAY for Debugging

Conditional Debugging

Error Logging

Data Validation and Error Prevention

Input Validation

Range and Format Validation

Best Practices and Guidelines

Error Handling Best Practices

Debugging Best Practices

Data Validation Best Practices

Common Pitfalls to Avoid

Test Your Knowledge

Frequently Asked Questions

What are the different types of errors that can occur in COBOL programs?

How do I implement comprehensive error handling in a COBOL program?

What is the difference between AT END and INVALID KEY clauses?

How can I debug errors in COBOL programs?

What are some best practices for error handling in COBOL?

Related Concepts

File Status Error Handling

Data Validation

Debugging Techniques

Exception Handling

Program Structure

Related Pages