Automate Cobol Processing With Control Cards: Optimize Your Code

In the realm of COBOL programming, understanding how to read control cards is paramount to harnessing the full potential of your programs. Control cards, akin to the blueprints of a program’s execution, govern its behavior and provide crucial input data. This blog post will guide you through the intricacies of reading control cards in COBOL, empowering you to effectively control and optimize your programs.

Anatomy of a Control Card

A control card is a special type of input record that precedes the actual data records in a COBOL program. It typically consists of the following components:

• Job Control Language (JCL): Instructions for the operating system, such as job name, resource requirements, and file assignments.
• COBOL Control Statements: Directives that control the execution of the COBOL program, including data definition, procedure invocation, and termination.
• User-Defined Parameters: Additional information that can be used within the COBOL program.

Reading Control Cards in COBOL

COBOL provides two methods for reading control cards:

Using the READ statement

The READ statement is commonly used to read control cards from an input device, such as a card reader or a file. Here’s the syntax:
“`
READ control-card-name [FROM file-name]
“`
where:

• control-card-name: A name assigned to the control card in the DATA DIVISION.
• file-name: The name of the file containing the control cards (optional).

Using the ACCEPT statement

The ACCEPT statement allows you to read control card data directly into variables. The syntax is:
“`
ACCEPT control-card-fields FROM control-card-name
“`
where:

• control-card-fields: A list of variables to be filled with data from the control card.
• control-card-name: The name of the control card in the DATA DIVISION.

Data Definition for Control Cards

Before reading control cards, it’s essential to define them in the DATA DIVISION using the CONTROL CARD clause. This clause specifies the layout and format of the control card data. Here’s an example:
“`
DATA DIVISION.
CONTROL CARD.
01 CONTROL-CARD-1.
05 JCL-FIELDS.
05 COBOL-FIELDS.
05 USER-FIELDS.
“`

Processing Control Card Data

Once control card data is read, you can process it using standard COBOL statements. For example, you can use the following statements to access and manipulate data from the JCL fields:
“`
MOVE JCL-FIELDS TO JCL-VAR
IF JCL-VAR = ‘RUN’ THEN
…
“`

Error Handling

It’s crucial to handle potential errors that may occur during control card reading. COBOL provides the following mechanisms:

• INVALID KEY: Raised when the record being read does not match the defined control card format.
• END-OF-FILE: Raised when the end of the control card file is reached.

Optimizing Control Card Reading

To optimize performance and efficiency, consider the following tips:

• Use the ACCEPT statement to read control card data directly into variables, avoiding the overhead of intermediate buffers.
• Define control cards in the DATA DIVISION as accurately as possible to minimize the risk of invalid key errors.
• Utilize the END-OF-FILE condition to handle the end of the control card file gracefully.

The Bottom Line: Mastering Control Card Reading

By mastering the techniques outlined in this post, you can effectively read and process control cards in your COBOL programs. This empowers you to tailor program execution, access user-defined parameters, and optimize performance. Embrace the power of control cards and unlock the full potential of your COBOL applications.

What You Need to Know

Q1: What are the advantages of using control cards in COBOL programs?
A1: Control cards provide a flexible way to control program execution, pass user-defined parameters, and optimize performance.
Q2: Can I read control cards from multiple files?
A2: Yes, you can specify multiple file names in the FROM clause of the READ statement to read control cards from different files.
Q3: How do I handle invalid control card data?
A3: Use the INVALID KEY condition to detect and handle invalid control card data, ensuring program stability.