COBOL Tutorial

COBOL File Status and Error Handling

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File Status Variables

File status variables are a critical component of robust COBOL file handling. They provide a standardized way to detect and respond to the results of file operations, allowing programs to handle both successful operations and various error conditions.

Declaring File Status

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ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE
        ASSIGN TO "CUSTOMER.DAT"
        ORGANIZATION IS SEQUENTIAL
        ACCESS MODE IS SEQUENTIAL
        FILE STATUS IS CUSTOMER-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  CUSTOMER-FILE
    LABEL RECORDS ARE STANDARD.
01  CUSTOMER-RECORD          PIC X(100).
 
WORKING-STORAGE SECTION.
01  CUSTOMER-STATUS          PIC XX.
    88  STATUS-SUCCESS       VALUE "00".
    88  END-OF-FILE          VALUE "10".
    88  FILE-NOT-FOUND       VALUE "35".

FILE STATUS IS clause in the SELECT statement links the file to a status variable
The status variable must be defined as a two-character field (PIC XX)
88-level condition names provide meaningful labels for common status codes
The status variable is automatically updated after each file operation

Basic Status Checking Pattern

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* Method 1: Direct status code comparison
OPEN INPUT CUSTOMER-FILE
IF CUSTOMER-STATUS = "00"
   PERFORM PROCESS-FILE
ELSE
   DISPLAY "Error opening file: " CUSTOMER-STATUS
END-IF
 
* Method 2: Using 88-level conditions
OPEN INPUT CUSTOMER-FILE
IF STATUS-SUCCESS
   PERFORM PROCESS-FILE
ELSE IF FILE-NOT-FOUND
   DISPLAY "Customer file not found"
   PERFORM CREATE-EMPTY-FILE
ELSE
   DISPLAY "Unexpected error: " CUSTOMER-STATUS
END-IF
 
* Method 3: Comprehensive condition handling
OPEN INPUT CUSTOMER-FILE
EVALUATE CUSTOMER-STATUS
   WHEN "00"
      PERFORM PROCESS-FILE
   WHEN "35"
      DISPLAY "File not found"
      PERFORM CREATE-EMPTY-FILE
   WHEN "37"
      DISPLAY "Access denied - check permissions"
   WHEN OTHER
      DISPLAY "Unexpected error: " CUSTOMER-STATUS
END-EVALUATE

These examples demonstrate different approaches to checking file status. The 88-level conditions and EVALUATE statement make the code more readable and maintainable compared to direct status code comparisons.

Extended File Status

Some COBOL implementations support an extended file status, which provides more detailed information about file operations.

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ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE
        ASSIGN TO "CUSTOMER.DAT"
        ORGANIZATION IS SEQUENTIAL
        FILE STATUS IS EXTENDED-STATUS.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  EXTENDED-STATUS.
    05  PRIMARY-STATUS       PIC XX.
        88  STATUS-SUCCESS   VALUE "00".
        88  END-OF-FILE      VALUE "10".
    05  SECONDARY-STATUS     PIC XXX.
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    OPEN INPUT CUSTOMER-FILE
    IF NOT STATUS-SUCCESS
       DISPLAY "Error: " PRIMARY-STATUS "-" SECONDARY-STATUS
       * Secondary status provides more details about the error
    END-IF

The extended file status typically consists of the standard two-character status code plus additional implementation-specific details in the secondary status. This provides more granular information about errors, helping with troubleshooting.

Benefits of File Status Checking

Provides immediate feedback on the result of file operations
Allows programs to handle errors gracefully rather than terminating
Supports detailed error reporting and logging
Enables sophisticated error recovery strategies
Makes programs more robust and production-ready
Standardized approach across different file organizations
Helps diagnose issues during development and production

Common File Status Codes

COBOL file status codes follow a structured pattern. The first digit generally indicates the category of the status, while the second digit provides more specific information. Understanding these codes is essential for effective error handling.

Status Code Categories

First Digit	Category	Description
0	Successful	Operation completed normally
1	At End	End of file or key range reached
2	Invalid Key	Key-related issue (indexed/relative files)
3	Permanent Error	Physical or hardware error
4	Logic Error	Program or operation sequence error
9	Implementor-Defined	Implementation-specific conditions

Common Status Codes for All File Types

Status	Description	Operations	Handling Approach
"00"	Successful completion	All operations	Continue normal processing
"10"	End of file reached	READ	Normal condition; finalize processing
"35"	File not found	OPEN INPUT, I-O	Create file or check path/name
"37"	File access denied	OPEN	Check permissions or file sharing
"39"	File attribute conflict	OPEN	Check record definition or ASSIGN
"41"	File already open	OPEN	Close file before reopening
"42"	File not open	CLOSE, READ, WRITE	Open file before operation
"43"	Required file access not taken	DELETE, REWRITE	READ record before operation
"46"	Read beyond file end	READ	Reset file position or check logic
"47"	File not open in required mode	I/O operations	Open file in correct mode
"48"	File locked	I/O operations	Wait and retry or check lock status
"90-99"	Implementation-defined error	Various	Check documentation for system

Status Codes Specific to Indexed Files

Status	Description	Operations	Handling Approach
"21"	Key sequence error	WRITE	Ensure records are in key sequence
"22"	Duplicate key	WRITE, REWRITE	Use unique key or update existing
"23"	Record not found	READ, REWRITE, DELETE	Verify key or handle missing record
"24"	Boundary violation	WRITE, START	Check key range or record size

Defining Condition Names for Status Codes

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WORKING-STORAGE SECTION.
01  FILE-STATUS-CODES.
    05  CUSTOMER-STATUS      PIC XX.
        * Success indicators
        88  STATUS-OK           VALUE "00".
        88  END-OF-FILE         VALUE "10".
        
        * Key-related errors
        88  DUPLICATE-KEY       VALUE "22".
        88  RECORD-NOT-FOUND    VALUE "23".
        
        * Open/access errors
        88  FILE-NOT-FOUND      VALUE "35".
        88  ACCESS-DENIED       VALUE "37".
        88  FILE-ALREADY-OPEN   VALUE "41".
        88  FILE-NOT-OPEN       VALUE "42".
        
        * General error classification
        88  OPERATION-SUCCESS   VALUE "00".
        88  AT-END-CONDITION    VALUE "10".
        88  KEY-ERROR           VALUE "21" "22" "23" "24".
        88  PERMANENT-ERROR     VALUE "30" THRU "39".
        88  LOGIC-ERROR         VALUE "40" THRU "49".
        88  SERIOUS-ERROR       VALUE "90" THRU "99".
 
* Usage example
READ CUSTOMER-FILE
IF STATUS-OK
   PROCESS-RECORD
ELSE IF END-OF-FILE
   PERFORM END-OF-PROCESSING
ELSE IF RECORD-NOT-FOUND
   DISPLAY "Customer record not found"
ELSE IF KEY-ERROR
   DISPLAY "Key error: " CUSTOMER-STATUS
END-IF

Using 88-level condition names makes code more readable and self-documenting. It allows logical grouping of status codes by both specific conditions and general categories.

File Status Interpretation Guidelines

Always consult your COBOL implementation's documentation for exact status code meanings
Status "00" always means success, regardless of implementation
Status "10" always indicates end-of-file for READ operations
The 2x series always relates to key violations in indexed or relative files
The 4x series typically indicates program logic errors that can be corrected
The 9x series often indicates serious or unrecoverable errors
Status codes can vary slightly between COBOL implementations
Create a standardized approach to status code handling across programs

Error Recovery Techniques

Effective error recovery goes beyond simply detecting errors through file status. Robust COBOL programs implement strategies to handle, recover from, and continue processing despite file-related issues.

Centralized Error Handling

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PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    IF NOT ERROR-OCCURRED
       PERFORM PROCESS-RECORDS UNTIL END-OF-FILE OR ERROR-OCCURRED
    END-IF
    PERFORM TERMINATION
    STOP RUN.
 
INITIALIZATION.
    OPEN INPUT CUSTOMER-FILE
    PERFORM CHECK-FILE-STATUS
    OPEN OUTPUT REPORT-FILE
    PERFORM CHECK-FILE-STATUS.
 
PROCESS-RECORDS.
    READ CUSTOMER-FILE
       AT END SET END-OF-FILE TO TRUE
    END-READ
    PERFORM CHECK-FILE-STATUS
    IF NOT END-OF-FILE AND NOT ERROR-OCCURRED
       PERFORM PROCESS-CUSTOMER
    END-IF.
 
CHECK-FILE-STATUS.
    EVALUATE TRUE
       WHEN STATUS-OK
          CONTINUE
       WHEN END-OF-FILE
          IF NOT CUSTOMER-OPERATION
             * End of file only valid for reads
             DISPLAY "Unexpected end of file"
             SET ERROR-OCCURRED TO TRUE
          END-IF
       WHEN FILE-NOT-FOUND
          DISPLAY "File not found: " CURRENT-FILE
          SET ERROR-OCCURRED TO TRUE
       WHEN OTHER
          DISPLAY "File error " FILE-STATUS " on " CURRENT-FILE
          DISPLAY "Operation: " CURRENT-OPERATION
          SET ERROR-OCCURRED TO TRUE
    END-EVALUATE.

A centralized error handling routine simplifies code maintenance and ensures consistent error handling throughout the program. The CHECK-FILE-STATUS paragraph is called after each file operation.

Automatic Retry for Transient Errors

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WORKING-STORAGE SECTION.
01  RETRY-VARIABLES.
    05  RETRY-COUNTER     PIC 9(3) VALUE ZERO.
    05  MAX-RETRIES       PIC 9(3) VALUE 3.
    05  RETRY-DELAY       PIC 9(3) VALUE 2.
 
PROCEDURE DIVISION.
FILE-OPERATION-WITH-RETRY.
    MOVE ZERO TO RETRY-COUNTER
    PERFORM UNTIL RETRY-COUNTER > MAX-RETRIES OR STATUS-OK
       ADD 1 TO RETRY-COUNTER
       
       * Attempt the file operation
       OPEN I-O CUSTOMER-FILE
       
       EVALUATE TRUE
          WHEN STATUS-OK
             CONTINUE
          WHEN FILE-LOCKED
             IF RETRY-COUNTER < MAX-RETRIES
                DISPLAY "File locked, retry " RETRY-COUNTER 
                        " of " MAX-RETRIES
                CALL "C$SLEEP" USING RETRY-DELAY
             ELSE
                DISPLAY "Maximum retries exceeded"
             END-IF
          WHEN OTHER
             * Non-retryable error
             DISPLAY "Fatal error: " FILE-STATUS
             MOVE MAX-RETRIES TO RETRY-COUNTER
       END-EVALUATE
    END-PERFORM.

This pattern implements an automatic retry mechanism for transient errors such as file locks in a multi-user environment. It includes a delay between attempts and limits the number of retries.

Alternative Processing Paths

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* Example: Handling a missing master file by using backup
PERFORM OPEN-MASTER-FILE
IF FILE-NOT-FOUND
   DISPLAY "Primary file not found, trying backup file"
   PERFORM OPEN-BACKUP-FILE
   IF STATUS-OK
      SET USING-BACKUP TO TRUE
      PERFORM LOG-BACKUP-USAGE
   ELSE
      DISPLAY "Cannot open primary or backup file"
      SET FATAL-ERROR TO TRUE
   END-IF
END-IF
 
* Example: Creating a file if it doesn't exist
OPEN I-O TRANSACTION-LOG
IF FILE-NOT-FOUND
   DISPLAY "Transaction log not found, creating new file"
   CLOSE TRANSACTION-LOG
   OPEN OUTPUT TRANSACTION-LOG
   IF STATUS-OK
      PERFORM WRITE-LOG-HEADER
      CLOSE TRANSACTION-LOG
      OPEN I-O TRANSACTION-LOG
   END-IF
END-IF
 
* Example: Skipping bad records and continuing
PERFORM UNTIL END-OF-FILE
   READ INPUT-FILE
      AT END SET END-OF-FILE TO TRUE
   END-READ
   
   IF NOT END-OF-FILE
      IF VALID-RECORD
         PERFORM PROCESS-RECORD
      ELSE
         ADD 1 TO ERROR-RECORD-COUNT
         PERFORM WRITE-TO-ERROR-FILE
      END-IF
   END-IF
END-PERFORM

These examples demonstrate different recovery strategies: falling back to backup files, automatically creating missing files, and skipping bad records to continue processing.

Comprehensive Error Logging

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IDENTIFICATION DIVISION.
PROGRAM-ID. ERRORLOG.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT ERROR-LOG
        ASSIGN TO "ERRORLOG.DAT"
        ORGANIZATION IS SEQUENTIAL
        ACCESS MODE IS SEQUENTIAL.
 
DATA DIVISION.
FILE SECTION.
FD  ERROR-LOG
    RECORD CONTAINS 200 CHARACTERS.
01  ERROR-RECORD                PIC X(200).
 
WORKING-STORAGE SECTION.
01  ERROR-LOG-FIELDS.
    05  LOG-TIMESTAMP           PIC X(26).
    05  LOG-PROGRAM-ID          PIC X(8).
    05  LOG-FILE-NAME           PIC X(30).
    05  LOG-OPERATION           PIC X(10).
    05  LOG-STATUS-CODE         PIC XX.
    05  LOG-RECORD-KEY          PIC X(20).
    05  LOG-MESSAGE             PIC X(100).
01  ERROR-LOG-RECORD.
    05  LOG-DATETIME            PIC X(26).
    05  FILLER                  PIC X VALUE '|'.
    05  LOG-PROGRAM             PIC X(8).
    05  FILLER                  PIC X VALUE '|'.
    05  LOG-FILE                PIC X(30).
    05  FILLER                  PIC X VALUE '|'.
    05  LOG-OPER                PIC X(10).
    05  FILLER                  PIC X VALUE '|'.
    05  LOG-STATUS              PIC XX.
    05  FILLER                  PIC X VALUE '|'.
    05  LOG-KEY                 PIC X(20).
    05  FILLER                  PIC X VALUE '|'.
    05  LOG-MSG                 PIC X(100).
 
PROCEDURE DIVISION.
LOG-FILE-ERROR.
    * Get current date and time
    MOVE FUNCTION CURRENT-DATE TO LOG-TIMESTAMP
    
    * Set log fields from parameters
    MOVE "CUSTMAIN" TO LOG-PROGRAM-ID
    MOVE "CUSTOMER.DAT" TO LOG-FILE-NAME
    MOVE "READ" TO LOG-OPERATION
    MOVE "23" TO LOG-STATUS-CODE
    MOVE "12345" TO LOG-RECORD-KEY
    MOVE "Customer record not found" TO LOG-MESSAGE
    
    * Format the log record
    PERFORM FORMAT-LOG-RECORD
    
    * Write to log file
    PERFORM WRITE-LOG-RECORD
    .
 
FORMAT-LOG-RECORD.
    MOVE LOG-TIMESTAMP TO LOG-DATETIME
    MOVE LOG-PROGRAM-ID TO LOG-PROGRAM
    MOVE LOG-FILE-NAME TO LOG-FILE
    MOVE LOG-OPERATION TO LOG-OPER
    MOVE LOG-STATUS-CODE TO LOG-STATUS
    MOVE LOG-RECORD-KEY TO LOG-KEY
    MOVE LOG-MESSAGE TO LOG-MSG
    .
 
WRITE-LOG-RECORD.
    OPEN EXTEND ERROR-LOG
    WRITE ERROR-RECORD FROM ERROR-LOG-RECORD
    CLOSE ERROR-LOG
    .

A robust error logging system captures detailed information about each error, including timestamp, program ID, file name, operation, status code, record key, and a descriptive message. This information is invaluable for troubleshooting.

Recovery Strategies for Specific Errors

Error Condition	Status Code	Recovery Strategy
File not found	"35"	Create file, use backup, or alert user
Duplicate key	"22"	Generate unique key or update existing record
Record not found	"23"	Create default record or skip processing
File locked	"48"	Implement retry mechanism with timeout
Disk full	"34"	Free space, use alternate location, or compress
Hardware error	"30"	Notify operations, use disaster recovery plan

AT END and INVALID KEY Clauses

COBOL provides two key structured error handling mechanisms for file operations: the AT END clause for sequential access and the INVALID KEY clause for indexed and relative files. These clauses complement file status checking and provide inline error handling.

AT END Clause

The AT END clause handles the condition when a READ operation attempts to read beyond the end of a file. This is commonly used with sequential file processing.

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* Basic AT END structure
READ CUSTOMER-FILE INTO WS-CUSTOMER-RECORD
   AT END
      SET END-OF-FILE TO TRUE
   NOT AT END
      ADD 1 TO RECORD-COUNT
      PERFORM PROCESS-CUSTOMER
END-READ
 
* Complete example with AT END
IDENTIFICATION DIVISION.
PROGRAM-ID. ATENDEXMP.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE
        ASSIGN TO "CUSTOMER.DAT"
        ORGANIZATION IS SEQUENTIAL
        ACCESS MODE IS SEQUENTIAL
        FILE STATUS IS CUSTOMER-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  CUSTOMER-FILE
    LABEL RECORDS ARE STANDARD.
01  CUSTOMER-RECORD          PIC X(100).
 
WORKING-STORAGE SECTION.
01  WS-CUSTOMER-RECORD       PIC X(100).
01  CUSTOMER-STATUS          PIC XX.
01  EOF-FLAG                 PIC X VALUE "N".
    88  END-OF-FILE            VALUE "Y".
01  RECORD-COUNT             PIC 9(5) VALUE ZERO.
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    PERFORM PROCESS-RECORDS UNTIL END-OF-FILE
    PERFORM TERMINATION
    STOP RUN.
 
INITIALIZATION.
    OPEN INPUT CUSTOMER-FILE
    IF CUSTOMER-STATUS NOT = "00"
       DISPLAY "Error opening file: " CUSTOMER-STATUS
       MOVE "Y" TO EOF-FLAG
    END-IF.
 
PROCESS-RECORDS.
    READ CUSTOMER-FILE INTO WS-CUSTOMER-RECORD
       AT END
          SET END-OF-FILE TO TRUE
          DISPLAY "End of file reached"
       NOT AT END
          ADD 1 TO RECORD-COUNT
          DISPLAY "Processing record " RECORD-COUNT
    END-READ
    
    * Check status for other errors
    IF NOT END-OF-FILE AND CUSTOMER-STATUS NOT = "00"
       DISPLAY "Error reading file: " CUSTOMER-STATUS
       MOVE "Y" TO EOF-FLAG
    END-IF.
 
TERMINATION.
    CLOSE CUSTOMER-FILE
    DISPLAY "Total records processed: " RECORD-COUNT.

AT END executes when the file pointer is positioned after the last record
NOT AT END executes when a record is successfully read
END-READ terminates the scope of the READ statement
AT END sets file status to "10" automatically
Additional file status checking can detect other errors

INVALID KEY Clause

The INVALID KEY clause handles key-related errors in indexed and relative files, such as record not found, duplicate key, or boundary violations.

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* Basic INVALID KEY structure
READ CUSTOMER-FILE
   KEY IS CUSTOMER-ID
   INVALID KEY
      DISPLAY "Customer " CUSTOMER-ID " not found"
   NOT INVALID KEY
      PERFORM PROCESS-CUSTOMER
END-READ
 
* INVALID KEY with WRITE
WRITE CUSTOMER-RECORD
   INVALID KEY
      EVALUATE CUSTOMER-STATUS
         WHEN "22"
            DISPLAY "Duplicate customer ID: " CUSTOMER-ID
         WHEN "24"
            DISPLAY "Key out of allowed range"
         WHEN OTHER
            DISPLAY "Error: " CUSTOMER-STATUS
      END-EVALUATE
   NOT INVALID KEY
      ADD 1 TO RECORDS-ADDED
END-WRITE
 
* Complete example with INVALID KEY
IDENTIFICATION DIVISION.
PROGRAM-ID. INVKEYEXMP.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE
        ASSIGN TO "CUSTOMER.IDX"
        ORGANIZATION IS INDEXED
        ACCESS MODE IS RANDOM
        RECORD KEY IS CUST-ID
        FILE STATUS IS CUSTOMER-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  CUSTOMER-FILE
    LABEL RECORDS ARE STANDARD.
01  CUSTOMER-RECORD.
    05  CUST-ID           PIC 9(5).
    05  CUST-NAME         PIC X(30).
    05  CUST-ADDRESS      PIC X(50).
    05  CUST-BALANCE      PIC S9(7)V99.
 
WORKING-STORAGE SECTION.
01  CUSTOMER-STATUS       PIC XX.
01  SEARCH-ID             PIC 9(5).
01  VALID-DATA            PIC X VALUE "Y".
01  PROCESSING-FLAG       PIC X VALUE "Y".
    88  CONTINUE-PROCESSING  VALUE "Y".
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    PERFORM UNTIL NOT CONTINUE-PROCESSING
       DISPLAY "Enter customer ID (0 to quit): "
       ACCEPT SEARCH-ID
       
       IF SEARCH-ID = 0
          MOVE "N" TO PROCESSING-FLAG
       ELSE
          PERFORM LOOKUP-CUSTOMER
       END-IF
    END-PERFORM
    PERFORM TERMINATION
    STOP RUN.
 
INITIALIZATION.
    OPEN I-O CUSTOMER-FILE
    IF CUSTOMER-STATUS NOT = "00"
       DISPLAY "Error opening file: " CUSTOMER-STATUS
       MOVE "N" TO PROCESSING-FLAG
    END-IF.
 
LOOKUP-CUSTOMER.
    MOVE SEARCH-ID TO CUST-ID
    READ CUSTOMER-FILE
       INVALID KEY
          EVALUATE CUSTOMER-STATUS
             WHEN "23"
                DISPLAY "Customer " SEARCH-ID " not found"
                DISPLAY "Would you like to add this customer? (Y/N)"
                ACCEPT VALID-DATA
                IF VALID-DATA = "Y"
                   PERFORM ADD-NEW-CUSTOMER
                END-IF
             WHEN OTHER
                DISPLAY "Error: " CUSTOMER-STATUS
          END-EVALUATE
       NOT INVALID KEY
          DISPLAY "Customer found: " CUST-NAME
          DISPLAY "Balance: " CUST-BALANCE
    END-READ.
 
ADD-NEW-CUSTOMER.
    MOVE SEARCH-ID TO CUST-ID
    DISPLAY "Enter customer name: "
    ACCEPT CUST-NAME
    DISPLAY "Enter customer address: "
    ACCEPT CUST-ADDRESS
    MOVE ZERO TO CUST-BALANCE
    
    WRITE CUSTOMER-RECORD
       INVALID KEY
          DISPLAY "Error adding customer: " CUSTOMER-STATUS
       NOT INVALID KEY
          DISPLAY "Customer added successfully"
    END-WRITE.
 
TERMINATION.
    CLOSE CUSTOMER-FILE.

INVALID KEY executes when a key-related error occurs
NOT INVALID KEY executes when the operation is successful
Applies to READ, WRITE, REWRITE, DELETE, and START operations
Automatically sets appropriate file status codes (e.g., "22", "23")
Can be combined with status checking for detailed error handling

Combining Clauses with File Status

For comprehensive error handling, combine AT END/INVALID KEY clauses with file status checking. This ensures that both expected conditions and unexpected errors are properly handled.

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* Example with both mechanisms
READ CUSTOMER-FILE NEXT RECORD
   AT END
      SET END-OF-FILE TO TRUE
   NOT AT END
      ADD 1 TO RECORD-COUNT
END-READ
 
* Check for other errors
IF NOT END-OF-FILE
   IF CUSTOMER-STATUS NOT = "00"
      DISPLAY "Error reading file: " CUSTOMER-STATUS
      PERFORM ERROR-HANDLING-ROUTINE
   ELSE
      PERFORM PROCESS-RECORD
   END-IF
END-IF
 
* Example for indexed file
READ CUSTOMER-FILE
   KEY IS CUSTOMER-ID
   INVALID KEY
      IF CUSTOMER-STATUS = "23"
         DISPLAY "Customer " CUSTOMER-ID " not found"
      ELSE
         DISPLAY "Unexpected key error: " CUSTOMER-STATUS
      END-IF
END-READ
 
* Additional status check for unexpected errors
IF CUSTOMER-STATUS NOT = "00" AND CUSTOMER-STATUS NOT = "23"
   DISPLAY "Serious error occurred: " CUSTOMER-STATUS
   PERFORM ERROR-RECOVERY-ROUTINE
END-IF

This pattern provides the most comprehensive error handling. The clauses handle expected conditions (end of file, record not found), while the file status checks catch any other unexpected errors.

Comparing Error Handling Approaches

Approach	Advantages	Limitations	Best For
File Status Only	Catches all error types, Centralized handling	More verbose code, Separated from file operation	Complex error recovery logic
AT END / INVALID KEY	Inline with operation, More readable	Limited to specific error types	Expected conditions in routine processing
Combined Approach	Comprehensive, Handles all scenarios	More complex code structure	Production systems requiring robust handling
88-Level Conditions	Readable code, Self-documenting	Requires additional definitions	Any approach for improved readability

Proper File Exception Handling

Proper file exception handling in COBOL combines all the techniques we've discussed into a comprehensive approach. This ensures that programs can detect, report, and recover from a wide range of file-related issues while maintaining data integrity.

Best Practices for File Exception Handling

Check file status after EVERY file operation - Never assume success
Use 88-level condition names - Makes code more readable and maintainable
Implement both structured clauses and status checking - For comprehensive coverage
Create a centralized error handling module - Ensures consistent handling
Log detailed error information - Include operation, file, status, and context
Implement graceful degradation - Allow partial processing when possible
Close files properly even after errors - Prevents resource leaks
Use appropriate recovery strategies - Based on specific error conditions
Consider transaction processing - For related updates requiring consistency
Include file status in all error messages - Aids in troubleshooting

Common Pitfalls to Avoid

Pitfall	Consequence	Better Approach
Ignoring file status	Undetected errors, data corruption	Check status after every operation
Relying only on AT END / INVALID KEY	Missing non-standard errors	Combine with status checking
Generic error handling	Limited recovery options	Error-specific recovery strategies
Not closing files after errors	Resource leaks, locked files	Close files in termination routine
Poor error messages	Difficult troubleshooting	Include operation, file, and status
Not validating input data	Preventable errors	Validate before file operations

Comprehensive File Handling Example

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IDENTIFICATION DIVISION.
PROGRAM-ID. FILEHDLR.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT CUSTOMER-FILE
        ASSIGN TO "CUSTOMER.IDX"
        ORGANIZATION IS INDEXED
        ACCESS MODE IS DYNAMIC
        RECORD KEY IS CUST-ID
        ALTERNATE RECORD KEY IS CUST-NAME WITH DUPLICATES
        FILE STATUS IS CUSTOMER-STATUS.
    
    SELECT ERROR-LOG
        ASSIGN TO "ERRORLOG.DAT"
        ORGANIZATION IS SEQUENTIAL
        ACCESS MODE IS SEQUENTIAL
        FILE STATUS IS LOG-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  CUSTOMER-FILE
    LABEL RECORDS ARE STANDARD.
01  CUSTOMER-RECORD.
    05  CUST-ID           PIC 9(5).
    05  CUST-NAME         PIC X(30).
    05  CUST-ADDRESS      PIC X(50).
    05  CUST-BALANCE      PIC S9(7)V99.
 
FD  ERROR-LOG
    LABEL RECORDS ARE STANDARD.
01  LOG-RECORD            PIC X(200).
 
WORKING-STORAGE SECTION.
01  FILE-STATUS-FIELDS.
    05  CUSTOMER-STATUS   PIC XX.
        88  CUST-SUCCESS    VALUE "00".
        88  CUST-EOF        VALUE "10".
        88  CUST-DUPLICATE  VALUE "22".
        88  CUST-NOT-FOUND  VALUE "23".
        88  CUST-NOT-EXISTS VALUE "35".
    05  LOG-STATUS        PIC XX.
    05  CURRENT-FILE      PIC X(30) VALUE SPACES.
    05  CURRENT-OPERATION PIC X(10) VALUE SPACES.
 
01  PROGRAM-FLAGS.
    05  ERROR-FLAG        PIC X VALUE "N".
        88  ERROR-OCCURRED  VALUE "Y".
    05  EOF-FLAG          PIC X VALUE "N".
        88  END-OF-FILE     VALUE "Y".
    05  RETRY-COUNTER     PIC 9(3) VALUE ZERO.
    05  MAX-RETRIES       PIC 9(3) VALUE 3.
 
01  SEARCH-ID             PIC 9(5).
01  LOG-FIELDS.
    05  LOG-TIMESTAMP     PIC X(26).
    05  LOG-FORMATTED     PIC X(200).
 
PROCEDURE DIVISION.
MAIN-PROCESS.
    PERFORM INITIALIZATION
    IF NOT ERROR-OCCURRED
       PERFORM PROCESS-RECORDS UNTIL END-OF-FILE OR ERROR-OCCURRED
    END-IF
    PERFORM TERMINATION
    STOP RUN.
 
INITIALIZATION.
    MOVE "CUSTOMER.IDX" TO CURRENT-FILE
    MOVE "OPEN" TO CURRENT-OPERATION
    
    OPEN I-O CUSTOMER-FILE
    PERFORM CHECK-FILE-STATUS
    
    IF CUST-NOT-EXISTS
       DISPLAY "Customer file not found. Creating new file."
       CLOSE CUSTOMER-FILE
       
       OPEN OUTPUT CUSTOMER-FILE
       PERFORM CHECK-FILE-STATUS
       
       IF NOT ERROR-OCCURRED
          CLOSE CUSTOMER-FILE
          OPEN I-O CUSTOMER-FILE
          PERFORM CHECK-FILE-STATUS
       END-IF
    END-IF.
 
PROCESS-RECORDS.
    DISPLAY "Enter customer ID (0 to quit): "
    ACCEPT SEARCH-ID
    
    IF SEARCH-ID = ZERO
       SET END-OF-FILE TO TRUE
    ELSE
       PERFORM READ-CUSTOMER
       
       IF NOT ERROR-OCCURRED
          IF CUST-NOT-FOUND
             DISPLAY "Customer not found. Add new customer? (Y/N)"
             ACCEPT EOF-FLAG
             IF EOF-FLAG = "Y"
                PERFORM ADD-CUSTOMER
             END-IF
          ELSE
             DISPLAY "Customer found: " CUST-NAME
             DISPLAY "Balance: " CUST-BALANCE
             
             DISPLAY "Update this customer? (Y/N)"
             ACCEPT EOF-FLAG
             IF EOF-FLAG = "Y"
                PERFORM UPDATE-CUSTOMER
             END-IF
          END-IF
       END-IF
    END-IF.
 
READ-CUSTOMER.
    MOVE "READ" TO CURRENT-OPERATION
    MOVE SEARCH-ID TO CUST-ID
    
    READ CUSTOMER-FILE
       INVALID KEY
          IF CUST-NOT-FOUND
             CONTINUE
          ELSE
             PERFORM LOG-ERROR
          END-IF
    END-READ
    
    PERFORM CHECK-FILE-STATUS.
 
ADD-CUSTOMER.
    MOVE "WRITE" TO CURRENT-OPERATION
    MOVE SEARCH-ID TO CUST-ID
    
    DISPLAY "Enter customer name: "
    ACCEPT CUST-NAME
    DISPLAY "Enter customer address: "
    ACCEPT CUST-ADDRESS
    MOVE ZERO TO CUST-BALANCE
    
    WRITE CUSTOMER-RECORD
       INVALID KEY
          PERFORM LOG-ERROR
       NOT INVALID KEY
          DISPLAY "Customer added successfully"
    END-WRITE
    
    PERFORM CHECK-FILE-STATUS.
 
UPDATE-CUSTOMER.
    MOVE "REWRITE" TO CURRENT-OPERATION
    
    DISPLAY "Enter new customer name (or ENTER to keep): "
    ACCEPT EOF-FLAG
    IF EOF-FLAG NOT = SPACES
       MOVE EOF-FLAG TO CUST-NAME
    END-IF
    
    DISPLAY "Enter new address (or ENTER to keep): "
    ACCEPT EOF-FLAG
    IF EOF-FLAG NOT = SPACES
       MOVE EOF-FLAG TO CUST-ADDRESS
    END-IF
    
    DISPLAY "Enter new balance (or ENTER to keep): "
    ACCEPT EOF-FLAG
    IF EOF-FLAG NOT = SPACES
       MOVE FUNCTION NUMVAL(EOF-FLAG) TO CUST-BALANCE
    END-IF
    
    REWRITE CUSTOMER-RECORD
       INVALID KEY
          PERFORM LOG-ERROR
       NOT INVALID KEY
          DISPLAY "Customer updated successfully"
    END-REWRITE
    
    PERFORM CHECK-FILE-STATUS.
 
CHECK-FILE-STATUS.
    EVALUATE TRUE
       WHEN CUST-SUCCESS
          CONTINUE
       WHEN CUST-EOF
          SET END-OF-FILE TO TRUE
       WHEN CUST-NOT-FOUND
          * Not an error for our program logic
          CONTINUE
       WHEN OTHER
          PERFORM LOG-ERROR
    END-EVALUATE.
 
LOG-ERROR.
    SET ERROR-OCCURRED TO TRUE
    DISPLAY "Error on " CURRENT-OPERATION " for " CURRENT-FILE
    DISPLAY "Status code: " CUSTOMER-STATUS
    
    * Log error to file
    MOVE FUNCTION CURRENT-DATE TO LOG-TIMESTAMP
    STRING LOG-TIMESTAMP DELIMITED BY SIZE
           " | FILEHDLR | "
           CURRENT-FILE DELIMITED BY SPACE
           " | " DELIMITED BY SIZE
           CURRENT-OPERATION DELIMITED BY SPACE
           " | " DELIMITED BY SIZE
           CUSTOMER-STATUS DELIMITED BY SIZE
           " | " DELIMITED BY SIZE
           "Cust ID: " DELIMITED BY SIZE
           CUST-ID DELIMITED BY SIZE
           INTO LOG-FORMATTED
    END-STRING
    
    MOVE "ERRORLOG.DAT" TO CURRENT-FILE
    MOVE "WRITE" TO CURRENT-OPERATION
    
    OPEN EXTEND ERROR-LOG
    IF LOG-STATUS = "00"
       MOVE LOG-FORMATTED TO LOG-RECORD
       WRITE LOG-RECORD
       CLOSE ERROR-LOG
    ELSE
       DISPLAY "Could not open error log"
    END-IF.
 
TERMINATION.
    MOVE "CLOSE" TO CURRENT-OPERATION
    CLOSE CUSTOMER-FILE
    IF CUSTOMER-STATUS NOT = "00"
       DISPLAY "Warning: Error closing " CURRENT-FILE
       DISPLAY "Status: " CUSTOMER-STATUS
    END-IF
    
    IF ERROR-OCCURRED
       DISPLAY "Program completed with errors"
    ELSE
       DISPLAY "Program completed successfully"
    END-IF.

This comprehensive example demonstrates best practices for file exception handling:

Status checking after every operation
Centralized error handling routine
Error logging to a separate file
Recovery strategies (creating missing files)
Proper file closing in termination
Using 88-level conditions for readability
Combining AT END/INVALID KEY with status checking
Detailed error information (operation, file, status)

File Handling in Multi-User Environments

In multi-user environments, additional considerations for file handling include:

Record locking - Preventing concurrent updates to the same record
File locking - Controlling access to an entire file
Deadlock prevention - Avoiding situations where processes wait for each other
Retry mechanisms - Handling temporary lock conditions
Transaction integrity - Ensuring related updates are atomic

cobol

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* Example of retry logic for locked records
PERFORM WITH TEST AFTER UNTIL STATUS-OK OR RETRY-COUNTER > MAX-RETRIES
   ADD 1 TO RETRY-COUNTER
   
   READ CUSTOMER-FILE WITH LOCK
      INVALID KEY
         PERFORM CHECK-INVALID-KEY
   END-READ
   
   IF CUSTOMER-STATUS = "48" OR CUSTOMER-STATUS = "9D"
      * Record or file is locked
      DISPLAY "Record locked, retry attempt " RETRY-COUNTER
      * Wait a moment before retrying
      CALL "C$SLEEP" USING 2
   END-IF
END-PERFORM
 
IF RETRY-COUNTER > MAX-RETRIES
   DISPLAY "Maximum retries exceeded - record still locked"
   SET ERROR-OCCURRED TO TRUE
END-IF

This example shows a retry mechanism for handling locked records in a multi-user environment. The program attempts to read the record multiple times with a delay between attempts.

Integration with System Recovery

Robust file exception handling should integrate with broader system recovery mechanisms:

Checkpoint/restart procedures - For recovering long-running processes
Backup and restore - For catastrophic failures
Transaction journals - For rolling back or forward after failures
Return codes - For communicating status to calling programs or JCL
Operational alerts - For notifying support staff of critical issues

By integrating file exception handling with these broader recovery mechanisms, COBOL programs can provide resilient and reliable file processing even in the face of various error conditions.

Test Your Knowledge

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

To allocate memory for file operations
To provide information on the result of file operations
To optimize the file for faster processing
To define file attributes in the FD entry

2. Which file status code indicates a successful file operation in COBOL?

"00"
"10"
"35"
"OK"

3. What is the file status code for "end of file reached" during a READ operation?

"00"
"10"
"23"
"40"

4. Which of the following is NOT a valid approach for handling file errors in COBOL?

Using the FILE STATUS clause in SELECT statements
Implementing the AT END clause for READ operations
Using the ACCEPT statement to retry failed operations automatically
Using the INVALID KEY clause for indexed file operations

5. What is the recommended practice for checking file status after operations?

Only check after operations that commonly fail
Check only the first character of the status code
Check status after every file operation
Check status only for write operations

COBOL Tutorial

COBOL File Status and Error Handling

File Status Variables

Declaring File Status

Basic Status Checking Pattern

Extended File Status

Benefits of File Status Checking

Common File Status Codes

Status Code Categories

Common Status Codes for All File Types

Status Codes Specific to Indexed Files

Defining Condition Names for Status Codes

File Status Interpretation Guidelines

Error Recovery Techniques

Centralized Error Handling

Automatic Retry for Transient Errors

Alternative Processing Paths

Comprehensive Error Logging

Recovery Strategies for Specific Errors

AT END and INVALID KEY Clauses

AT END Clause

INVALID KEY Clause

Combining Clauses with File Status

Comparing Error Handling Approaches

Proper File Exception Handling

Best Practices for File Exception Handling

Common Pitfalls to Avoid

Comprehensive File Handling Example

File Handling in Multi-User Environments

Integration with System Recovery

Test Your Knowledge

Frequently Asked Questions

Related Concepts

Sequential File Operations

Indexed File Operations

Exception Handling

File Organization Types

ENVIRONMENT DIVISION

Related Pages

COBOL Tutorial

COBOL File Status and Error Handling

File Status Variables

Declaring File Status

Basic Status Checking Pattern

Extended File Status

Benefits of File Status Checking

Common File Status Codes

Status Code Categories

Common Status Codes for All File Types

Status Codes Specific to Indexed Files

Defining Condition Names for Status Codes

File Status Interpretation Guidelines

Error Recovery Techniques

Centralized Error Handling

Automatic Retry for Transient Errors

Alternative Processing Paths

Comprehensive Error Logging

Recovery Strategies for Specific Errors

AT END and INVALID KEY Clauses

AT END Clause

INVALID KEY Clause

Combining Clauses with File Status

Comparing Error Handling Approaches

Proper File Exception Handling

Best Practices for File Exception Handling

Common Pitfalls to Avoid

Comprehensive File Handling Example

File Handling in Multi-User Environments

Integration with System Recovery

Test Your Knowledge

Frequently Asked Questions

How do I implement proper file status checking in COBOL?

What are the most important file status codes I should know?

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

How should I handle file errors in a batch processing environment?

What techniques can I use to recover from file errors?

Related Concepts

Sequential File Operations

Indexed File Operations

Exception Handling

File Organization Types

ENVIRONMENT DIVISION

Related Pages