Lesson 5
Handling Errors in File Operations
Handling Errors in File Operations

As we advance in our journey of learning COBOL file handling, it's essential to address the practical aspects of working with files, such as dealing with errors. In previous lessons, we've learned how to create, read, write, and append records to both sequential and indexed files. In this lesson, we'll explore how to handle errors that can arise during file operations, ensuring that your programs are robust and reliable.

What You'll Learn

In this lesson, you'll learn how to implement error handling in COBOL file operations. Mistakes can happen: a file might not exist, a read operation might fail, or issues could occur while writing to a file. We'll focus on checking file statuses and responding to errors gracefully.

Let's look at an example:

cobol
1IDENTIFICATION DIVISION.
2PROGRAM-ID. ErrorHandlingDemo.
3ENVIRONMENT DIVISION.
4INPUT-OUTPUT SECTION.
5FILE-CONTROL.
6    SELECT InputFile ASSIGN TO 'non-existing-file.dat'
7    ORGANIZATION IS SEQUENTIAL
8    FILE STATUS IS WS-FILE-STATUS.
9DATA DIVISION.
10FILE SECTION.
11FD  InputFile.
1201  InputRecord.
13    05 Customer-Name PIC X(30).
14    05 Account-Number PIC 9(10).
15    05 Account-Balance PIC 9(8)V99.
16WORKING-STORAGE SECTION.
1701 WS-FILE-STATUS PIC XX VALUE '00'.
18PROCEDURE DIVISION.
19    OPEN INPUT InputFile
20        IF WS-FILE-STATUS NOT = '00'
21            DISPLAY "Error opening file: " WS-FILE-STATUS
22            STOP RUN.
23    CLOSE InputFile.
24    STOP RUN.

In this snippet, we attempt to open a non-existing file and check the file status to handle the error appropriately.

Let's analyze the essential components of the code:

  • We first define the file structure as before, with the FILE-CONTROL and FILE SECTION sections.
  • We introduce a new variable, WS-FILE-STATUS, to store the file status, with an initial value of '00'. This variable will hold the status of file operations; if the file doesn't exist, the value will be set to a non-zero value. Note, that this variable is referenced in the FILE STATUS IS clause in the FILE-CONTROL section, which specifies the file status variable.
  • We attempt to open the file using the OPEN INPUT statement and check the file status using the IF condition.
    • If the file status is not equal to '00', we display an error message and stop the program.
    • The file status '00' indicates that the file operation was successful.

Since we do not have the file non-existing-file.dat, the OPEN INPUT operation will fail, and the file status will be set to a non-zero value. We check this status and display an error message if the file opening operation fails.

When you run this program, you should see the following output:

1Error opening file: 35
Why Error Handling is Important

Error handling in COBOL is crucial for building reliable applications, especially in critical systems such as banking or financial platforms. Without proper error handling, your program might fail silently, producing incorrect results or crashing unexpectedly. Here are some reasons why mastering error handling is vital:

  • Ensures Program Stability: Helps your program handle unexpected situations gracefully.
  • Improves User Experience: Provides meaningful error messages to users rather than abrupt failures.
  • Facilitates Debugging: Makes it easier to identify and fix issues in your code.
  • Critical for Real-world Applications: Essential for applications that handle critical data, where errors can have substantial consequences.

Exciting, right? Understanding and implementing effective error-handling techniques in your COBOL programs will enhance the reliability and user experience, making your applications more robust and professional.

Ready to dive in and see error handling in action? Let's move on to the practice section and solidify your understanding!

Enjoy this lesson? Now it's time to practice with Cosmo!
Practice is how you turn knowledge into actual skills.