In COBOL file handling, what are the different OPEN modes available for files and what does each mode imply about how the file will be used?

Introduction / Context:
COBOL programs work with files in a variety of ways, including reading, writing, updating, and appending records. The OPEN statement tells the runtime how the program intends to use each file, which affects whether the file must already exist, whether records can be updated, and where new records are placed. This question focuses on the standard file OPEN modes in COBOL and what each one implies.

Given Data / Assumptions:

• Files are defined in the ENVIRONMENT DIVISION and DATA DIVISION with appropriate organization and access mode.
• The program uses the OPEN statement before performing I O operations on a file.
• COBOL offers different OPEN modes rather than a single universal mode.
• The question asks for the main modes and their basic meanings.

Concept / Approach:
The standard COBOL OPEN modes are INPUT, OUTPUT, I-O, and EXTEND. INPUT opens an existing file for reading only; records cannot be added or changed. OUTPUT creates a new file or overwrites an existing one and opens it for writing; it is typically used to create a fresh output file. I-O opens an existing file for both reading and updating, allowing the program to read records and then rewrite or delete them. EXTEND opens an existing sequential file for appending new records at the end without disturbing existing content.

Step-by-Step Solution:
Step 1: Match INPUT mode with read only processing of an existing file. Step 2: Match OUTPUT mode with creating or replacing a file and writing new records from the beginning. Step 3: Match I-O mode with the ability to both read and update or delete records in a file that already exists. Step 4: Match EXTEND mode with appending new records at the end of an existing sequential file.

Verification / Alternative check:
COBOL language references describe these four modes consistently and provide examples of OPEN INPUT, OPEN OUTPUT, OPEN I-O, and OPEN EXTEND. The descriptions emphasize that the selected mode must match both the file organization and the intended operations. There is no mention of modes named READONLY, TEST, or ABEND in standard COBOL syntax, which confirms that the correct option is the one listing INPUT, OUTPUT, I-O, and EXTEND.

Why Other Options Are Wrong:
Option B introduces fictitious modes and associates them only with VSAM, which is not accurate for the language standard. Option C lists items that sound like debugging controls rather than file modes. Option D is wrong because COBOL requires explicit OPEN statements, and files are not automatically opened for all access types. Option E suggests a single UPDATE mode, which does not exist in COBOL syntax.

Common Pitfalls:
A common pitfall is opening a file in the wrong mode, such as opening a file in INPUT when updates are required, which leads to runtime errors. Another frequent error is using OUTPUT when the intention was to append, unintentionally overwriting existing data. Some developers forget to verify that a file exists before using I-O or EXTEND. Understanding the meaning of each OPEN mode helps prevent data loss and ensures that file operations behave as intended in COBOL applications.

Final Answer:
The main COBOL OPEN modes are INPUT for reading, OUTPUT for creating and writing a new file, I-O for both reading and updating an existing file, and EXTEND for appending records at the end of an existing file