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COBOL Tutorial

COBOL NOT ON EXCEPTION - Quick Reference

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Overview

The NOT ON EXCEPTION clause in COBOL handles the successful completion of operations. It executes when an operation completes successfully, allowing the program to continue with normal processing flow.

Purpose and Usage

  • Success handling for operations
  • Normal flow processing after successful operations
  • Complementary to ON EXCEPTION for complete error handling
  • Clear separation of success and error logic

Syntax

The NOT ON EXCEPTION clause follows specific syntax patterns:

Basic Syntax

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* Basic NOT ON EXCEPTION syntax
statement ON EXCEPTION
    * Exception handling code
    PERFORM error-handling
NOT ON EXCEPTION
    * Success handling code
    PERFORM success-processing
END-EXCEPTION.

NOT ON EXCEPTION handles successful operations.

File Operation Example

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* File operation with success handling
OPEN INPUT data-file
    ON EXCEPTION
        DISPLAY "Error opening file: " data-file
        PERFORM file-error-handling
    NOT ON EXCEPTION
        DISPLAY "File opened successfully"
        PERFORM process-file
        PERFORM continue-processing
END-EXCEPTION.

Method Invocation Example

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* Method invocation with success handling
INVOKE object "method-name" USING parameter
    ON EXCEPTION
        DISPLAY "Method call failed"
        PERFORM method-error-handling
    NOT ON EXCEPTION
        DISPLAY "Method executed successfully"
        PERFORM process-results
        PERFORM continue-processing
END-EXCEPTION.

Practical Examples

Here are some practical uses of NOT ON EXCEPTION in COBOL:

File Processing with Success Handling

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* Reading file with success handling
READ data-file
    ON EXCEPTION
        IF file-status = "10"
            DISPLAY "End of file reached"
            PERFORM end-of-file-processing
        ELSE
            DISPLAY "Read error: " file-status
            PERFORM read-error-handling
        END-IF
    NOT ON EXCEPTION
        PERFORM process-record
        ADD 1 TO records-processed
        DISPLAY "Record processed successfully"
END-EXCEPTION.
 
* Writing file with success handling
WRITE output-record
    ON EXCEPTION
        DISPLAY "Write error: " file-status
        PERFORM write-error-handling
    NOT ON EXCEPTION
        ADD 1 TO records-written
        DISPLAY "Record written successfully"
END-EXCEPTION.

Comprehensive file I/O with success handling.

Object Method Success Handling

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* Database connection with success handling
INVOKE database "Connect" USING connection-string
    ON EXCEPTION
        DISPLAY "Database connection failed"
        PERFORM database-error-handling
        MOVE "N" TO connection-success
    NOT ON EXCEPTION
        DISPLAY "Database connected successfully"
        MOVE "Y" TO connection-success
        PERFORM database-operations
        PERFORM continue-processing
END-EXCEPTION.
 
* Data validation with success handling
INVOKE validator "ValidateData" USING input-data
    ON EXCEPTION
        DISPLAY "Data validation failed"
        PERFORM validation-error-handling
    NOT ON EXCEPTION
        DISPLAY "Data validation successful"
        PERFORM process-valid-data
        PERFORM continue-processing
END-EXCEPTION.

Object method success handling for robust operations.

Best Practices

  • Use NOT ON EXCEPTION to handle successful operations explicitly.
  • Provide clear success messages for debugging and monitoring.
  • Perform necessary cleanup or continuation logic in success blocks.
  • Update counters or status indicators for successful operations.
  • Continue normal program flow after successful operations.
  • Test both success and error paths thoroughly.

Common Pitfalls

  • Forgetting to handle successful operations explicitly.
  • Not updating status indicators or counters for successful operations.
  • Missing continuation logic after successful operations.
  • Not providing appropriate success messages for monitoring.
  • Assuming operations will always succeed without proper handling.

Test Your Knowledge

1. What is the primary purpose of the NOT ON EXCEPTION clause in COBOL?

  • To handle errors
  • To handle successful operations
  • To terminate the program
  • To skip statements

2. When does NOT ON EXCEPTION execute?

  • When an error occurs
  • When an operation completes successfully
  • Always
  • Never

3. What is the relationship between ON EXCEPTION and NOT ON EXCEPTION?

  • They are the same
  • ON EXCEPTION handles errors, NOT ON EXCEPTION handles success
  • NOT ON EXCEPTION is obsolete
  • They cannot be used together

4. Is NOT ON EXCEPTION required when using ON EXCEPTION?

  • Yes, always
  • No, it is optional
  • Only for file operations
  • Only for method calls

5. What should you typically do in NOT ON EXCEPTION blocks?

  • Handle errors
  • Process successful results and continue normal flow
  • Terminate the program
  • Skip to the next statement

Frequently Asked Questions

Related Concepts

ON EXCEPTION

Handling errors and exceptions in COBOL.

Error Handling

Comprehensive error handling strategies.

File Operations

File I/O with success and error handling.

INVOKE Statement

Method invocation with exception handling.

Robust Programming

Best practices for reliable COBOL programs.

ON EXCEPTIONPOINTER-32