Input Fields, Output Fields, and Both Fields

Learning Objective

By the end of this lesson, you will be able to explain the difference between an input field, an output field, and a "both" field on a 5250 screen, and recognize why this distinction matters to an RPGLE program.

Simple Explanation

In the DDS Field Definitions lesson, you learned that a DDS field definition specifies a field's name, data type, and length. A field defined inside a display file's record format has one more important property: its usage, which states how that field is meant to be used on the screen.

Three common usage types cover most fields you will encounter:

• Input fields let the user type a value in, which the RPGLE program then reads after the screen is submitted, such as a customer number entry field.
• Output fields are filled in by the RPGLE program and displayed to the user, but the user cannot type into them, such as a customer's name or balance shown as a lookup result.
• Both fields can work in either direction: the RPGLE program can display a value in them, and the user can also type a new value into the same field, useful for something like a quantity field that starts with a suggested value the user can change.

Why It Matters

Understanding field usage explains exactly how information moves between an RPGLE program and the person using a 5250 screen: input fields carry information from the user to the program, output fields carry information from the program to the user, and both fields allow information to flow both ways in the same field. Getting this right is essential to designing a screen that behaves the way you intend.

Practical Example

Imagine the customer inquiry screen from earlier lessons in this group. The customer number field is an input field: the user types a value in, and the RPGLE program reads it to know which customer to look up. The customer name and balance fields are output fields: the RPGLE program fills them in after the lookup, and the user only sees the result rather than being able to change it directly on this screen.

Now imagine a different screen where a user can adjust a suggested order quantity before confirming it. That quantity field would commonly be a both field: the RPGLE program displays a suggested starting quantity, and the user can type a different value before submitting the screen.

This is a simplified, illustrative example rather than a specific real screen, but it reflects a very common, practical use of all three field usage types.

Common Confusions

"Can a user type into an output field?" No. An output field is meant only to display information the RPGLE program provides; the user cannot type into it. If a field needs to accept typed input, it needs to be defined as an input field or a both field instead.

"Is a both field the same as having two separate fields, one input and one output, in the same spot?" No. A both field is a single field definition that supports both directions at once: the program can set an initial value, and the user can then change it, all within that one field, rather than needing two separate field definitions layered on top of each other.

"Does the RPGLE program need to do anything different to read an input field versus a both field?" Generally, no. Once the screen is submitted, the RPGLE program reads whatever value is currently in an input field or a both field the same way; the meaningful difference is in what the user was allowed to do with that field on the screen itself.

Quick Recap

• A DDS field's usage states how it behaves on screen: input, output, or both.
• Input fields let a user type a value the RPGLE program reads; output fields display a value the program provides, without allowing typed input.
• Both fields combine the two: the program can display a starting value, and the user can change it.
• Choosing the right field usage is essential to designing a screen that behaves the way you intend.

Try Asking the AI Tutor

Use the AI Tutor to ask follow-up questions about this lesson. For example, try asking:

• "What happens if I accidentally define a field that should be input-only as output instead?"
• "Are there other field usage types beyond input, output, and both?"