Ted Holt
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Guru: Global Variables in Modules
December 13, 2021 Ted Holt
When I first learned to program computers (RPG II, COBOL 74), the only kind of variables I knew of were global variables. Any statement within a program was able to use any variable. It was not until I started my computer science degree that I found out about local variables, which are known to only part of a program. Since that time, it has been my practice to use local variables as much as possible and global variables only when necessary.
Ideally an RPG program, service program, module, or subprocedure would have no global variables at all, but I don’t …
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The Four Hundred Guru Retires
December 13, 2021 Ted Holt
This is the last issue of The Four Hundred for which I am serving as technical editor.
I have been editing the technical content of and writing articles for this august publication for 20 years. For most of that time, this has been a side job that I’ve done outside of normal working hours (i.e., nights and weekends). I’m ready for a change. Technical editing and writing are not easy and they take a lot of time, time that I had rather spend doing other things.
In the days ahead I plan to spend:
- Less time sitting and more time
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Guru: Abstract Data Types and RPG
November 8, 2021 Ted Holt
An abstract data type (ADT) is a type of data and a set of operations defined over that type of data. Using ADTs allows a programmer to work with data in terms of functionality rather than physical representation. The ADT is the basis of object-oriented programming. Does that mean that abstract data types don’t apply to procedural languages like RPG? Not at all. Quite the contrary.
Before I show you how you can use abstract data types in RPG-based applications, let me further illustrate abstract data types with another, non-OO object — the user profile. The user profile is a …
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Guru: Flexible Interfaces
November 1, 2021 Ted Holt
The details are murky, it’s been eons ago. Probably the mid-1990’s. I was working on an AS/400 that ran a mixture of System/36 and native applications. I needed to call a program that had been written in the latest version of RPG from both S/36 RPG II and native RPG III (a.k.a. RPG/400) programs. I hope I’m remembering this correctly. It’s been so long.
The problem I ran into was rooted in a numeric parameter. S/36 programs passed numeric parameters in zoned decimal format, whereas native RPG and CL programs used packed decimal. The called program defined the parameter as …
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Guru: Quick And Handy RPG Output, Take 2
October 25, 2021 Ted Holt
I am pleased today to revisit a topic I wrote about just over seven and a half years ago. I do so for two reasons. First, I’ve made a slight improvement to my routine. Second, I’d like to provide more examples of this routine in action. My previous article suffered from a paucity of examples. I can’t believe I let that happen.
I’m talking about the writeln subprocedure, a handy routine that I use to write unstructured text to a spooled file. I derived the inspiration for this routine from Pascal, a programming language I used heavily when I was …
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Guru: What Is Constant Folding And Why Should I Care About It?
October 18, 2021 Ted Holt
Constant folding is a compiler-optimization technique, whereby the compiler replaces calculations that involve constants with the result values when possible. Constant folding is common in modern compilers, and according to the RPG reference, the RPG compiler uses this technique. (See the documentation of the %div and %rem functions, for example.)
But you and I don’t write compilers. We write business applications. Why then should we care about constant folding? That’s a question worth pondering.
Consider how I used to have to write RPG in the Dark Ages.
C MOVE CUSTNR CUSTSV 50
Here I’m copying the customer account number to …
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Guru: Alternate SQL Row-Selection Criteria Revisited Revisited
September 27, 2021 Ted Holt
I am not a “do as I say and not as I do” kind of person. After I wrote the article Guru: Alternate SQL Row-Selection Criteria Revisited, I got serious about using dynamic SQL in my RPG programs instead of enabling and disabling logical expressions in the WHERE clause. I’m reliving the days when OPNQRYF was my best friend, trying to make apostrophes play nice with string concatenation.
Overall, I’m happy with the change. When I have converted the switch-laden version to dynamic SQL, I have seen a noticeable performance improvement in some cases, and at least a slight …
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Guru: Another Red Flag – Joining On Expressions
August 30, 2021 Ted Holt
One would think that a given datum, for example a sales order number, would be defined identically in the various database tables in which it is found within an organization, but one might be wrong. I have on many occasions faced the challenge of joining two or more tables on unmatched data types.
But it gets worse than that. Sometimes joins involve expressions, which may consist of mathematical operations and/or invocations of functions, both intrinsic and user-written. As with the word DISTINCT in a SELECT, the presence of expression in a join sends up a little red flag that …
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Guru: Set Beats A Loop
August 23, 2021 Ted Holt
Hey, Ted:
I’m sending you some RPG source code that I put into one of our inquiry programs and would like to have your insight. Instead of using the SETLL, DOW and READE opcodes to loop through a group of selected records, I used the SQL SET statement. This seems to me much easier for someone else to understand and follow. Is this good practice?
— Mike
I was glad to see Mike’s email in my inbox, as always. He and I met in person at the RPG & DB2 Summit a few years ago, and I’ve enjoyed getting to …
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Guru: Odds and Ends
August 16, 2021 Ted Holt
I really appreciate the comments that readers add to the end of articles or send to me in email. The more you share, the more all of us are better off. I know that you don’t have time to go back through articles we have published to see if anyone has commented, so this week I do that for you. Please keep the feedback coming!
Several people posted responses to Paul Tuohy’s article Getting Meaningful Audit Information from a Journal. You can read them for yourself, but I wanted to thank Emanuele, who mentioned a tool that is similar …
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