EXCEPT opcode in rpg

19 Views

Prev
Next

In RPGLE (IBM i), the EXCEPT operation code is used in traditional (fixed-format) RPG to write output to a printer file (PRTF) using an output specification defined in the program or external file.

It is rarely used in modern Free-Form RPG, but still important to understand for maintaining legacy applications.

🧾 What EXCEPT Does

  • It writes a record to a printer file based on a named output specification.

  • The format must be defined in O-specs in the source, or externally in the printer file.

📘 Example (Fixed-Format RPG)

Assume a printer file MYREPORT is defined with a record format named DETAIL.

FMYREPORT O   F   132        PRINTER
DName        S             30A
DAge         S              3S 0

C             EXCEPT DETAIL
ODETAIL   E            Name Age

  • EXCEPT DETAIL writes the output line defined in the ODETAIL specification.

  • The fields Name and Age are placed at specific positions.

⚙️ Key Notes

Feature Description
Output only EXCEPT is used only for writing, not reading
PRINTER files only Works with files defined with PRINTER device
O-Spec Required Needs output specs (O-specs) or externally described formats
Used in reports Common in old-style report generation

🚫 Not Used in Free-Form RPG

  • In modern free-form RPG, EXCEPT is generally not used.

  • Instead, output is handled with WRITE or SQL/IFS/logs depending on the context.

✅ Summary

  • EXCEPT writes output lines to printer files using a named output spec.

  • It's a legacy opcode, used primarily in fixed-format RPG for printed report generation.

  • Modern programs avoid EXCEPT in favor of WRITE, free-form printing, or SQL-based reporting.

----------------------------------------------------------------------------------------------------------------------------------------------

Great question.

🔒 Does EXCEPT Lock a File in RPGLE?

No, the EXCEPT operation does not lock a file or record in the traditional sense.

📘 Why?

  • EXCEPT is used to write output to a printer file (PRTF)—not a database file.

  • Printer files do not involve record-level locking like database files do.

  • It simply sends a formatted line to the spool file or printer output.

⚙️ Details:

Feature EXCEPT Behavior
Used for Report printing (not DB I/O)
Locks file? ❌ No – no record or file locking
Device Type PRINTER
Concurrency Safe – multiple jobs can write to their own spool files independently

✅ Summary

  • EXCEPT is strictly for formatted report writing.

  • It does not lock any files or records.

  • Locking concerns apply to database files (PF/LF) accessed with CHAIN, READ, UPDATE, etc.—not to printer files used with EXCEPT.

If you're seeing unexpected behavior around locking, it may involve other files in your program, not the EXCEPT itself. I can help you analyze that too.

----------------------------------------------------------------------------------------------------------------------------------

No, you cannot update a database file using the EXCEPT opcode in RPGLE.

🔍 What EXCEPT Does and Doesn't Do

Feature EXCEPT Behavior
Used for Writing output lines to a printer file
Updates database file? ❌ No
Inserts new DB records? ❌ No
Device type PRINTER device only
Associated file type O-spec output or external printer formats

✅ If You Want to Update a File in RPGLE

Use these opcodes instead (for database files):

Opcode Purpose
CHAIN Retrieve a record by key
READ Read a sequential record
UPDATE Update a locked record
WRITE Add a new record
DELETE Delete an existing record

🧠 Example (Correct Way to Update a Record):

dcl-f MyFile usage(*update) keyed;

chain keyField MyFile;
if %found(MyFile);
   MyField = 'NewValue';
   update MyFile;
endif;

✅ Summary

  • EXCEPT is not used for updating or manipulating database files.

  • It is used only for writing output lines to a printer file (e.g., report generation).

  • For database updates, use CHAIN + UPDATE, or SQL UPDATE statements.

---------------------------------------------------------------------------------------------------------------------------

Yes, in AS/400 RPGLE interviews—especially for legacy system roles—you might encounter questions about the EXCEPT opcode. Here's how such interview questions are typically framed and how you can respond:

💬 Common Interview Questions on EXCEPT Opcode

✅ 1. What is the purpose of the EXCEPT opcode in RPG?

Answer:

The EXCEPT opcode is used in traditional RPG (especially fixed-format) to write output records to a printer file. It references a named output specification (O-spec), which defines how the output line should be formatted. It is typically used for generating reports or printed documents.

✅ 2. Can EXCEPT be used to update or write to database files?

Answer:

No. EXCEPT is used only with printer files, not database files. For updating database records, we use opcodes like UPDATE, WRITE, DELETE, and CHAIN.

✅ 3. What’s the difference between EXCEPT and WRITE in RPG?

Answer:

Feature EXCEPT WRITE
File type Printer file Database or printer file
Needs record format? Yes, defined in O-spec or externally Yes
Used in Report generation Writing records (DB or print)
Modern use? Rare / legacy Common in free-form RPG

✅ 4. Is EXCEPT still used in modern RPG programming?

Answer:

Rarely. Modern RPG (free-form) and reporting tools typically use WRITE, embedded SQL, or external reporting tools (like Query/400, DB2 Web Query, or JasperReports). EXCEPT is mainly seen in legacy RPG III or RPG IV (fixed-format) programs.

✅ 5. What happens if the named EXCEPT format doesn’t exist?

Answer:

If the format is not defined in the O-specs or in the external printer file, the compiler will throw an error during compilation, as EXCEPT needs a valid output format to write to.

✅ Pro Tip for Interviews

If you're asked about EXCEPT, the interviewer is likely checking:

  • Your familiarity with legacy RPG practices

  • Whether you know the difference between printer vs. database file handling

  • Your adaptability to modern techniques

 

Prev
Next
Save ()

Post Comments