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.
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:
cobol1IDENTIFICATION 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:
FILE-CONTROL
and FILE SECTION
sections.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.OPEN INPUT
statement and check the file status using the IF
condition.
'00'
, we display an error message and stop the program.'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
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:
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!