COBOL Tutorial

Input Validation in COBOL

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Introduction to Input Validation

Input validation is the process of checking and verifying data as it enters a COBOL program from external sources such as files, user terminals, or databases. Proper input validation ensures data quality, prevents processing errors, and maintains data integrity throughout your application.

Why Input Validation Matters

Prevents garbage-in, garbage-out scenarios that corrupt downstream processing
Catches errors early in the processing pipeline, reducing debugging time
Maintains data quality standards across all applications
Provides audit trails for invalid data attempts
Protects against processing failures and system crashes
Ensures compliance with business rules and data standards

Key Input Validation Strategies

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* Validate as early as possible
PERFORM READ-INPUT-RECORD
IF FILE-STATUS NOT = "00"
   PERFORM HANDLE-FILE-ERROR
   EXIT PARAGRAPH
END-IF
 
PERFORM VALIDATE-RECORD-STRUCTURE
IF NOT VALID-RECORD
   PERFORM HANDLE-INVALID-RECORD
   GO TO READ-NEXT-RECORD
END-IF
 
PERFORM VALIDATE-ALL-FIELDS
IF NOT VALID-DATA
   PERFORM LOG-VALIDATION-ERRORS
   WRITE ERROR-RECORD
   GO TO READ-NEXT-RECORD
END-IF
 
* Process validated record
PERFORM PROCESS-VALID-RECORD.

Validation should happen early in the processing flow, before any business logic is applied.

File I/O Validation

When reading from files, COBOL programs must validate both the file operations and the data being read. This includes checking file status codes, verifying record formats, and ensuring data integrity.

File Status Validation

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IDENTIFICATION DIVISION.
PROGRAM-ID. FILEVALID.
DATA DIVISION.
FILE SECTION.
FD  INPUT-FILE
    FILE STATUS IS WS-INPUT-STATUS.
01  INPUT-RECORD         PIC X(80).
 
WORKING-STORAGE SECTION.
01  WS-INPUT-STATUS      PIC XX.
    88  SUCCESSFUL-READ   VALUE "00".
    88  END-OF-FILE       VALUE "10".
    88  LOGICAL-EOF        VALUE "46".
    88  READ-ERROR         VALUE "30" "94" "96" "97".
    
01  WS-FILE-ERROR-MSG    PIC X(80).
 
PROCEDURE DIVISION.
INITIALIZATION.
    OPEN INPUT INPUT-FILE
    EVALUATE WS-INPUT-STATUS
        WHEN "00"
            DISPLAY "File opened successfully"
        WHEN "35"
            MOVE "File not found" TO WS-FILE-ERROR-MSG
            PERFORM ABEND-PROGRAM
        WHEN OTHER
            MOVE "Error opening file" TO WS-FILE-ERROR-MSG
            MOVE WS-INPUT-STATUS TO WS-FILE-ERROR-MSG(20:2)
            PERFORM ABEND-PROGRAM
    END-EVALUATE.
 
READ-AND-VALIDATE.
    READ INPUT-FILE
         AT END SET END-OF-FILE TO TRUE
    END-READ
    
    EVALUATE WS-INPUT-STATUS
        WHEN SUCCESSFUL-READ
            CONTINUE
        WHEN END-OF-FILE
            GO TO END-OF-PROCESSING
        WHEN LOGICAL-EOF
            GO TO END-OF-PROCESSING
        WHEN READ-ERROR
            MOVE "Read error occurred" TO WS-FILE-ERROR-MSG
            PERFORM LOG-ERROR
            GO TO READ-AND-VALIDATE
        WHEN OTHER
            MOVE "Unexpected file status" TO WS-FILE-ERROR-MSG
            MOVE WS-INPUT-STATUS TO WS-FILE-ERROR-MSG(25:2)
            PERFORM LOG-ERROR
    END-EVALUATE.

Always check FILE STATUS after file operations to handle errors gracefully.

Record Length and Format Validation

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IDENTIFICATION DIVISION.
PROGRAM-ID. RECVALID.
DATA DIVISION.
WORKING-STORAGE SECTION.
01  INPUT-RECORD         PIC X(200).
01  INPUT-RECORD-LENGTH  PIC 9(3) VALUE 80.
 
01  VALIDATION-SWITCHES.
    05  VALID-RECORD-SW   PIC X VALUE "Y".
        88  VALID-RECORD  VALUE "Y".
        88  INVALID-REC   VALUE "N".
    05  ERROR-FLAG        PIC X VALUE SPACE.
    
01  ERROR-MESSAGE        PIC X(100).
 
PROCEDURE DIVISION.
READ-INPUT-FILE.
    READ INPUT-FILE
         AT END GO TO END-OF-PROCESSING
    END-READ
    
    * Check record length
    PERFORM VALIDATE-RECORD-LENGTH
    IF NOT VALID-RECORD
       GO TO READ-INPUT-FILE
    END-IF
    
    * Validate record format
    PERFORM VALIDATE-RECORD-FORMAT
    IF NOT VALID-RECORD
       GO TO READ-INPUT-FILE
    END-IF
    
    * Process valid record
    PERFORM PROCESS-RECORD
    GO TO READ-INPUT-FILE.
 
VALIDATE-RECORD-LENGTH.
    MOVE "Y" TO VALID-RECORD-SW
    MOVE FUNCTION LENGTH(INPUT-RECORD) TO INPUT-RECORD-LENGTH
    
    IF INPUT-RECORD-LENGTH NOT = 80
        MOVE "Record length is not 80 characters" TO ERROR-MESSAGE
        MOVE "N" TO VALID-RECORD-SW
        MOVE "L" TO ERROR-FLAG
        PERFORM LOG-ERROR
    END-IF.
    
    EXIT.
 
VALIDATE-RECORD-FORMAT.
    MOVE "Y" TO VALID-RECORD-SW
    
    * Check if record starts with expected identifier
    IF INPUT-RECORD(1:3) NOT = "HDR" AND 
       INPUT-RECORD(1:3) NOT = "DTL" AND
       INPUT-RECORD(1:3) NOT = "TRL"
        MOVE "Invalid record type identifier" TO ERROR-MESSAGE
        MOVE "N" TO VALID-RECORD-SW
        MOVE "T" TO ERROR-FLAG
        PERFORM LOG-ERROR
    END-IF.
    
    EXIT.

Validate record structure and length before attempting to access individual fields.

Input Field Validation

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01  INPUT-FIELDS.
    05  CUSTOMER-NUMBER   PIC X(10).
    05  TRANSACTION-DATE  PIC X(10).
    05  TRANSACTION-AMT   PIC X(12).
    05  TRANSACTION-TYPE  PIC X.
        88  VALID-TRANS-TYPE VALUE "S" "P" "R" "C".
    05  PRODUCT-CODE      PIC X(15).
    
01  VALIDATION-WORK-AREAS.
    05  WS-CUSTOMER-NUM   PIC 9(10).
    05  WS-TRANS-DATE     PIC 9(8).
    05  WS-TRANS-AMOUNT   PIC 9(8)V99.
    05  VALID-FIELD-SW    PIC X VALUE "Y".
        88  FIELD-VALID   VALUE "Y".
        88  FIELD-INVALID VALUE "N".
 
VALIDATE-INPUT-FIELDS.
    MOVE "Y" TO VALID-FIELD-SW
    
    * Validate customer number
    IF CUSTOMER-NUMBER IS NOT NUMERIC
        MOVE "Customer number must be numeric" TO ERROR-MSG
        MOVE "N" TO VALID-FIELD-SW
        PERFORM LOG-FIELD-ERROR
        MOVE "CUSTOMER-NUMBER" TO ERROR-FIELD-NAME
    END-IF
    
    * Validate and convert transaction date
    IF TRANSACTION-DATE IS NOT NUMERIC
        MOVE "Transaction date must be numeric" TO ERROR-MSG
        MOVE "N" TO VALID-FIELD-SW
        PERFORM LOG-FIELD-ERROR
        MOVE "TRANSACTION-DATE" TO ERROR-FIELD-NAME
    ELSE
        MOVE TRANSACTION-DATE TO WS-TRANS-DATE
        PERFORM VALIDATE-DATE-FORMAT
        IF NOT FIELD-VALID
            MOVE "Invalid date format" TO ERROR-MSG
            PERFORM LOG-FIELD-ERROR
        END-IF
    END-IF
    
    * Validate transaction amount
    IF TRANSACTION-AMT IS NOT NUMERIC
        MOVE "Transaction amount must be numeric" TO ERROR-MSG
        MOVE "N" TO VALID-FIELD-SW
        PERFORM LOG-FIELD-ERROR
        MOVE "TRANSACTION-AMT" TO ERROR-FIELD-NAME
    ELSE
        MOVE TRANSACTION-AMT TO WS-TRANS-AMOUNT
        IF WS-TRANS-AMOUNT <= ZERO
            MOVE "Transaction amount must be greater than zero" TO ERROR-MSG
            MOVE "N" TO VALID-FIELD-SW
            PERFORM LOG-FIELD-ERROR
            MOVE "TRANSACTION-AMT" TO ERROR-FIELD-NAME
        END-IF
    END-IF
    
    * Validate transaction type
    IF NOT VALID-TRANS-TYPE
        MOVE "Invalid transaction type" TO ERROR-MSG
        MOVE "N" TO VALID-FIELD-SW
        PERFORM LOG-FIELD-ERROR
        MOVE "TRANSACTION-TYPE" TO ERROR-FIELD-NAME
    END-IF
    
    * Validate product code format
    IF PRODUCT-CODE(1:3) IS NOT ALPHABETIC
        MOVE "Product code must start with 3 letters" TO ERROR-MSG
        MOVE "N" TO VALID-FIELD-SW
        PERFORM LOG-FIELD-ERROR
        MOVE "PRODUCT-CODE" TO ERROR-FIELD-NAME
    ELSE
        IF PRODUCT-CODE(4:1) NOT = "-"
            MOVE "Product code must have hyphen at position 4" TO ERROR-MSG
            MOVE "N" TO VALID-FIELD-SW
            PERFORM LOG-FIELD-ERROR
            MOVE "PRODUCT-CODE" TO ERROR-FIELD-NAME
        END-IF
    END-IF.

Validate each input field individually and provide specific error messages for each validation failure.

User Input Validation

In interactive COBOL programs, user input requires immediate validation with feedback to the user. This ensures data quality and provides a better user experience.

Interactive Input with Validation

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01  USER-INPUT-AREAS.
    05  ACCOUNT-NUMBER-INPUT PIC X(10).
    05  ACCOUNT-BALANCE      PIC 9(7)V99.
    05  DEPOSIT-AMOUNT-INPUT PIC X(10).
    05  DEPOSIT-AMOUNT       PIC 9(7)V99.
    
01  VALIDATION-FLAGS.
    05  VALID-INPUT-SW      PIC X.
        88  VALID-INPUT     VALUE "Y".
        88  INVALID-INPUT   VALUE "N".
    05  ERROR-DISPLAY-SW    PIC X VALUE "N".
        88  SHOW-ERROR      VALUE "Y".
 
ACCEPT-AND-VALIDATE-ACCOUNT.
    DISPLAY "Enter account number (10 digits): "
    ACCEPT ACCOUNT-NUMBER-INPUT
    
    MOVE "Y" TO VALID-INPUT-SW
    
    * Validate account number
    IF ACCOUNT-NUMBER-INPUT IS NOT NUMERIC
        DISPLAY "ERROR: Account number must contain only digits"
        MOVE "N" TO VALID-INPUT-SW
    ELSE
        IF FUNCTION LENGTH(ACCOUNT-NUMBER-INPUT) NOT = 10
            DISPLAY "ERROR: Account number must be exactly 10 digits"
            MOVE "N" TO VALID-INPUT-SW
        END-IF
    END-IF
    
    * Continue validation loop until input is valid
    PERFORM UNTIL VALID-INPUT
        IF INVALID-INPUT
            DISPLAY "Please re-enter account number: "
            ACCEPT ACCOUNT-NUMBER-INPUT
            
            MOVE "Y" TO VALID-INPUT-SW
            IF ACCOUNT-NUMBER-INPUT IS NOT NUMERIC
                DISPLAY "ERROR: Account number must contain only digits"
                MOVE "N" TO VALID-INPUT-SW
            ELSE
                IF FUNCTION LENGTH(ACCOUNT-NUMBER-INPUT) NOT = 10
                    DISPLAY "ERROR: Account number must be exactly 10 digits"
                    MOVE "N" TO VALID-INPUT-SW
                END-IF
            END-IF
        END-IF
    END-PERFORM.
    
    EXIT.
 
ACCEPT-AND-VALIDATE-AMOUNT.
    PERFORM UNTIL VALID-INPUT
        DISPLAY "Enter deposit amount (max 9999999.99): "
        ACCEPT DEPOSIT-AMOUNT-INPUT
        
        MOVE "Y" TO VALID-INPUT-SW
        
        IF DEPOSIT-AMOUNT-INPUT IS NOT NUMERIC
            DISPLAY "ERROR: Amount must be numeric"
            MOVE "N" TO VALID-INPUT-SW
        ELSE
            MOVE DEPOSIT-AMOUNT-INPUT TO DEPOSIT-AMOUNT
            
            IF DEPOSIT-AMOUNT <= ZERO
                DISPLAY "ERROR: Amount must be greater than zero"
                MOVE "N" TO VALID-INPUT-SW
            ELSE
                IF DEPOSIT-AMOUNT > 9999999.99
                    DISPLAY "ERROR: Amount exceeds maximum of 9999999.99"
                    MOVE "N" TO VALID-INPUT-SW
                END-IF
            END-IF
        END-IF
        
        IF INVALID-INPUT
            DISPLAY "Please try again."
        END-IF
    END-PERFORM.
    
    EXIT.

Provide immediate feedback and allow users to correct invalid input in interactive programs.

Batch Processing Error Handling

In batch processing, invalid input records should not stop the entire job. Instead, they should be logged and written to an error file for later correction.

Error File Management

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IDENTIFICATION DIVISION.
PROGRAM-ID. BATCHVALID.
DATA DIVISION.
FILE SECTION.
FD  INPUT-FILE.
01  INPUT-RECORD           PIC X(200).
 
FD  VALID-FILE.
01  VALID-RECORD           PIC X(200).
 
FD  ERROR-FILE.
01  ERROR-RECORD.
    05  ERR-DATE           PIC X(8).
    05  ERR-TIME           PIC X(8).
    05  ERR-INPUT-RECORD   PIC X(200).
    05  ERR-MESSAGE        PIC X(100).
 
WORKING-STORAGE SECTION.
01  WS-PROCESSING-STATS.
    05  WS-RECORDS-READ    PIC 9(7) VALUE ZERO.
    05  WS-RECORDS-VALID   PIC 9(7) VALUE ZERO.
    監視WS-RECORDS-ERROR   PIC 9(7) VALUE ZERO.
    
01  VALIDATION-SWITCHES.
    05  VALID-RECORD-SW    PIC X.
        88  VALID-RECORD   VALUE "Y".
        88  INVALID-REC    VALUE "N".
 
MAIN-PROCESSING.
    OPEN INPUT  INPUT-FILE
         OUTPUT VALID-FILE
         OUTPUT ERROR-FILE
    
    PERFORM UNTIL END-OF-FILE
        READ INPUT-FILE
             AT END SET END-OF-FILE TO TRUE
        END-READ
        
        IF NOT END-OF-FILE
            ADD 1 TO WS-RECORDS-READ
            MOVE "Y" TO VALID-RECORD-SW
            
            * Perform all validations
            PERFORM VALIDATE-INPUT-RECORD
            
            IF VALID-RECORD
                WRITE VALID-RECORD FROM INPUT-RECORD
                ADD 1 TO WS-RECORDS-VALID
            ELSE
                PERFORM WRITE-ERROR-RECORD
                ADD 1 TO WS-RECORDS-ERROR
            END-IF
        END-IF
    END-PERFORM
    
    CLOSE INPUT-FILE
          VALID-FILE
          ERROR-FILE
    
    PERFORM PRINT-SUMMARY-STATISTICS
    STOP RUN.
 
VALIDATE-INPUT-RECORD.
    * Validate record type
    IF INPUT-RECORD(1:3) = SPACES
        MOVE "Invalid record: Record type is blank" TO ERROR-MSG
        MOVE "N" TO VALID-RECORD-SW
        EXIT PARAGRAPH
    END-IF
    
    * Validate key field
    PERFORM VALIDATE-KEY-FIELDS
    IF NOT VALID-RECORD
        EXIT PARAGRAPH
    END-IF
    
    * Validate data fields
    PERFORM VALIDATE-DATA-FIELDS
    IF NOT VALID-RECORD
        EXIT PARAGRAPH
    END-IF
    
    EXIT.
 
WRITE-ERROR-RECORD.
    MOVE FUNCTION CURRENT-DATE(1:8) TO ERR-DATE
    MOVE FUNCTION CURRENT-DATE(9:6) TO ERR-TIME
    MOVE INPUT-RECORD TO ERR-INPUT-RECORD
    MOVE ERROR-MSG TO ERR-MESSAGE
    WRITE ERROR-RECORD
    EXIT.

Batch programs should continue processing and collect statistics on valid and invalid records.

Exercise: Building a Comprehensive Input Validator

Create a COBOL program that reads customer transaction records and validates all input fields:

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IDENTIFICATION DIVISION.
PROGRAM-ID. EXERCISE01.
 
DATA DIVISION.
FILE SECTION.
FD  INPUT-FILE.
01  TRANSACTION-RECORD.
    05  RECORD-TYPE       PIC XX.
    05  CUSTOMER-ID       PIC X(10).
    05  TRANSACTION-DATE  PIC X(10).
    05  TRANSACTION-TYPE  PIC X.
    就05  AMOUNT            PIC X(12).
    05  FILLER            PIC X(146).
    
FD  VALID-OUTPUT-FILE.
01  VALID-OUTPUT-REC      PIC X(180).
 
FD  ERROR-OUTPUT-FILE.
01  ERROR-OUTPUT-REC.
    05  ERR-DATE          PIC X(8).
    05  ERR-TIME          PIC X(6).
    05  ERR-INPUT         PIC X(180).
    05  ERR-MESSAGE       PIC X(100).
 
WORKING-STORAGE SECTION.
01  WS-SWITCHES.
    05  EOF-SW            PIC X VALUE "N".
        88  END-OF-FILE   VALUE "Y".
    05  VALID-REC-SW      PIC X VALUE "Y".
        88  VALID-RECORD  VALUE "Y".
        88  INVALID-REC   VALUE "N".
 
01  WS-WORK-FIELDS.
    05  WS-CUST-ID        PIC 9(10).
    05  WS-TRANS-DATE     PIC 9(8).
    05  WS-AMOUNT         PIC 9(8)V99.
    
01  WS-STATISTICS.
    05  WS-TOTAL-READ     PIC 9(7) VALUE ZERO.
    05  WS-TOTAL-VALID    PIC 9(7) VALUE ZERO.
    05  WS-TOTAL-ERROR    PIC 9(7) VALUE ZERO.
 
* Implement the following:
* 1. Record type validation (must be "DT")
* 2. Customer ID validation (must be 10 numeric digits)
* 3. Transaction date validation (format YYYYMMDD)
* 4. Transaction type validation (must be "D" or "W" or "P")
* 5. Amount validation (must be numeric and > 0)
 
PROCEDURE DIVISION.
MAIN.
    OPEN INPUT  INPUT-FILE
         OUTPUT VALID-OUTPUT-FILE
         OUTPUT ERROR-OUTPUT-FILE
    
    PERFORM UNTIL END-OF-FILE
        READ INPUT-FILE
             AT END SET END-OF-FILE TO TRUE
        END-READ
        
        IF NOT END-OF-FILE
            ADD 1 TO WS-TOTAL-READ
            MOVE "Y" TO VALID-REC-SW
            
            PERFORM VALIDATE-TRANSACTION
            
            IF VALID-RECORD
                WRITE VALID-OUTPUT-REC FROM TRANSACTION-RECORD
                ADD 1 TO WS-TOTAL-VALID
            ELSE
                PERFORM WRITE-ERROR
                ADD 1 TO WS-TOTAL-ERROR
            END-IF
        END-IF
    END-PERFORM
    
    CLOSE INPUT-FILE
          VALID-OUTPUT-FILE
          ERROR-OUTPUT-FILE
    
    DISPLAY "Total records read: " WS-TOTAL-READ
    DISPLAY "Valid records: " WS-TOTAL-VALID
    DISPLAY "Error records: " WS-TOTAL-ERROR
    
    STOP RUN.
 
VALIDATE-TRANSACTION.
* Implement validation logic here
    EXIT.
 
WRITE-ERROR.
* Implement error writing logic here
    EXIT.

Implement the validation logic for all fields and proper error handling in the provided program.

Knowledge Check

Test Your Knowledge

1. Which validation technique should be performed first when reading input in COBOL?

Range checking
Format validation
Business rule validation
Cross-field validation

2. What is the purpose of the FILE STATUS clause in COBOL?

To check if data is valid
To determine file opening success
To indicate the position in the file
To validate record format

3. When reading records from a file, what is the best practice for validating the record length?

Assume all records are the correct length
Check record length against a maximum length only
Validate record length matches expected format before processing
Skip validation for performance

4. How should you handle input records that fail validation in a batch program?

Stop processing immediately
Skip to the next record
Write to an error file and continue processing
Attempt to correct the data automatically

5. What is a common technique for validating formatted input data like dates or codes?

Using REDEFINES to break down the data into components
Using only basic numeric checks
Skipping format validation
Using random validation

Frequently Asked Questions

Error Recovery Internationalization

COBOL Tutorial

Input Validation in COBOL

Introduction to Input Validation

Why Input Validation Matters

Key Input Validation Strategies

File I/O Validation

File Status Validation

Record Length and Format Validation

Input Field Validation

User Input Validation

Interactive Input with Validation

Batch Processing Error Handling

Error File Management

Exercise: Building a Comprehensive Input Validator

Knowledge Check

Test Your Knowledge

Frequently Asked Questions

Why is input validation critical in COBOL batch processing?

What are the main types of input validation needed in COBOL programs?

How do you validate input from different sources (sequential files, indexed files, user input)?

What is the difference between input validation and data validation?

How can COBOL programs validate input against master files or reference tables?