READ, WRITE, EXFMT, and Screen Flow

Learning Objective

By the end of this lesson, you will understand that exfmt is really a combination of separate write and read operations, and recognize a situation where using them separately makes more sense than exfmt alone.

Simple Explanation

In the RPGLE Program Calling a Display File lesson, you learned that exfmt shows a record format and reads the user's response in one combined step, and that this lesson group would return to what that actually means underneath. As it turns out, exfmt is built from two separate, more basic operations:

• write sends a record format to the screen, without waiting for the user to respond at all. Control returns to the program immediately after the screen is shown.
• read waits for the user to respond to a record format already on the screen, without sending anything new first.

exfmt is simply write followed immediately by read, combined into one operation, which is why it is the most common, straightforward choice for a simple screen where you want to show something and immediately wait for the response.

Using write and read separately becomes useful when a program needs to show something to the user, then do other work, before waiting for their response:

write PROCESSINGFMT;

// Do some longer-running work here while
// PROCESSINGFMT stays visible on screen

read INQFMT;

Here, write PROCESSINGFMT; shows a "please wait" style message immediately, without pausing the program. The program can then do other work while that message stays visible, before separately using read to wait for a response to a different format already expected on screen.

Why It Matters

Understanding that exfmt is write plus read demystifies what exfmt is actually doing, and gives you the flexibility to separate those two steps when a program genuinely needs to show something and keep working before waiting for a response, rather than always pausing immediately the way exfmt does.

Practical Example

Imagine a program that needs to show a "Processing your request..." message while it performs a longer lookup or calculation, before finally showing the result and waiting for the user. Using write to show the processing message immediately, doing the actual work afterward, and then using exfmt or read for the next screen keeps the user informed during the wait, rather than leaving the screen frozen with no feedback until the work finishes.

This is a simplified, illustrative example rather than a specific real program, but it reflects a genuinely common, practical reason to use write and read separately instead of relying only on exfmt.

Common Confusions

"Should I replace every exfmt in my programs with separate write and read calls?" No. For the very common case of showing a screen and immediately waiting for the user's response, exfmt remains the simplest, most direct choice, exactly as used throughout earlier lessons in this group. Separate write and read calls are most useful specifically when work needs to happen between showing something and waiting for a response.

"Does write wait for the user at all?" No. write sends a record format to the screen and returns control to the program immediately, without waiting for any response. Waiting for a response is specifically what read does.

"Can I use read on a record format that hasn't been written to the screen yet?" No, not meaningfully. read waits for a response to a record format already visible on the screen, so it depends on that format having been shown first, whether through an earlier write or exfmt call.

Quick Recap

• exfmt combines write (show a format, do not wait) and read (wait for a response to a format already shown) into one operation.
• write alone is useful for showing something, such as a "please wait" message, while the program continues working before waiting for a response.
• read alone waits for a response to a record format that has already been written to the screen.
• exfmt remains the simplest, most common choice when a program wants to show a screen and immediately wait for the user.

Try Asking the AI Tutor

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

• "What are some other realistic reasons to use write and read separately instead of exfmt?"
• "Does write need to be paired with a matching read on the exact same record format?"