19
Sun, May
7 New Articles

RPG Academy: Write Better Code—A Few More Naming Variables Guidelines

RPG
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

It’s time to discuss a few more variable prefixes and a technique you can resort to when you’re forced by the circumstances to use indicators, namely when you manipulate display and printer files.

 

The last installment of this series covered parameter and work variable prefixes, which are arguably the most-used variables in a typical RPG program. However, I recommend taking a few more steps and using separate variables for key fields and constants as well. Keep reading to find out why.

 

More Naming Variables Guidelines: Key Field Variable and Constant Prefixes

Besides the parameter and work variables mentioned in the previous TechTip, there are others that are equally important and often neglected, leading to hours and hours of wasted time looking for an error. I’m talking about key fields.

 

Don’t forget K_ for key fields. Just like P_, I use this prefix to isolate keys to database operations, thus making sure that whichever value I started with is not lost when the file is read.

 

This principle might not be clear, so let me show you an example:

 

/FREE

SETLL MYFIELD MYFILE;

READ MYFILE;

DOW NOT %EOF(MYFILE);

   // The cursor is positioned and the first record was read

   // do something with it...

   READ MYFILE;

ENDDO;

/END-FREE

 

If MYFIELD is a field from MYFILE, but with a value that I got from somewhere else or composed from other fields, I would lose that value when I read the file. That’s why I prefer to use K_ prefixed variables:

 

/FREE

SETLL K_MYFIELD MYFILE;

READ MYFILE;

DOW NOT %EOF(MYFILE);

   // The cursor is positioned and the first record was read

   // do something with it...

   READ MYFILE;

ENDDO;

/END-FREE

 

There’s another group of fields that are sometimes used as part of keys to files, among other things: the constants. They also require a prefix.

 

Use C_ for constants. This is one of those prefixes that are critical for me. Did you ever try to assign a value to a variable and get a strange error from the compiler that didn’t make sense? Well, usually those errors occur when you try to assign a value to something defined as a constant. By using the C_ prefix, you make your constants easily identifiable.

 

Here’s an example of a constant (in this case, it indicates the maximum size of an array):

 

DCL-C C_MaxArraySize CONST(999);

 

Constants are not only easier to identify, they also improve performance. Because of their definition, they’re not handled like regular variables. The system acknowledges them for what they are, constants, and doesn’t treat them as plain old variables.

 

Now let’s discuss that named indicator technique I mentioned previously. Naturally, I’ll start by assigning a prefix to all indicator-related variables.

 

Use I_ for named indicators. I really hate indicators, but there are (still) times when I’m forced to used them. When that happens, I try to turn their non-human-readable numbers into something that makes sense, like turning *IN10 into I_SflDsp.

 

Sound interesting? To do it, start by defining a pointer over the memory address assigned to the indicators, like this:

 

// **************************************************************

//   Redefinition of indicators

// **************************************************************

// Definition of Indicator Pointer

DCL-S IndicatorPtr POINTER Inz (%Addr(*In));

 

Then, build a data structure based on that pointer:

 

// Specification of Indicators

DCL-DS *N Based(IndicatorPtr);

      INDLST CHAR(99);

END-DS;

 

After this, you can create groups of indicators for error-handling purposes, like this:

 

DCL-S ErrIndicators IND Overlay (INDLST: 31) Dim (40);

 

Alternatively, you can assign individual, human-readable names to each of them:

 

// **************************************************************

// Description of screen indicators

// **************************************************************

// General indicators

DCL-S I_DspMsgSfl IND Overlay (INDLST: 02);

DCL-S I_Hardcopy IND Overlay (INDLST: 03);

DCL-S I_PageDown IND Overlay (INDLST: 04);

DCL-S I_PageUp IND Overlay (INDLST: 05);

DCL-S I_Help IND Overlay (INDLST: 06);

DCL-S I_Home IND Overlay (INDLST: 07);

DCL-S I_SflDsp IND Overlay (INDLST: 10);

DCL-S I_SflDspCtl IND Overlay (INDLST: 11);

DCL-S I_SflClr IND Overlay (INDLST: 12);

 

Note that these are all part of the data structure built over the pointer shown before. If you want to assign more meaningful names to the indicators related to the error messages (or if you have to, because you still use message file-based error messages in display files), you can. It would look something like this:

 

// Error Indicators (I_XXYYYYYYYA)

//                      | |     |)

//                     | |     Letter (For reused MSGs on same scr)

//                     | Message ID

//                      Screen ID

 

// Indicators screen INVINPC1

DCL-S I_C1DBO0038 IND Overlay (INDLST: 35);

 

I try to avoid indicators as much as I can and, for most things, that’s possible. With a little creativity and some study, you’ll find that you can use something called “program to display file” fields, or P-Fields, defined in the DDS source, to eliminate the usage of indicators for most of the attributes. The hexadecimal values needed to set them can be found in the SDA Programming Guide under the section for the DSPATR keyword. Unfortunately, as far as I know, P-Fields do not support the MDT, OID, PC, and SP attributes; of this group of attributes, only the Position Cursor (PC) can be eliminated by using the CSRLOC keyword. It’s possible to use a service program that calls the List Field API (QUSLFLD) over the display file and retrieves the row and column for the field in question.

 

I’m sure some of the readers don’t agree with the prefix scheme described here. Feel free to share your ideas about this topic in an open and constructive discussion in the comments section below or in one of the LinkedIn groups where RPG Academy’s TechTips usually pop up!

Rafael Victoria-Pereira

Rafael Victória-Pereira has more than 20 years of IBM i experience as a programmer, analyst, and manager. Over that period, he has been an active voice in the IBM i community, encouraging and helping programmers transition to ILE and free-format RPG. Rafael has written more than 100 technical articles about topics ranging from interfaces (the topic for his first book, Flexible Input, Dazzling Output with IBM i) to modern RPG and SQL in his popular RPG Academy and SQL 101 series on mcpressonline.com and in his books Evolve Your RPG Coding and SQL for IBM i: A Database Modernization Guide. Rafael writes in an easy-to-read, practical style that is highly popular with his audience of IBM technology professionals.

Rafael is the Deputy IT Director - Infrastructures and Services at the Luis Simões Group in Portugal. His areas of expertise include programming in the IBM i native languages (RPG, CL, and DB2 SQL) and in "modern" programming languages, such as Java, C#, and Python, as well as project management and consultancy.


MC Press books written by Rafael Victória-Pereira available now on the MC Press Bookstore.

Evolve Your RPG Coding: Move from OPM to ILE...and Beyond Evolve Your RPG Coding: Move from OPM to ILE...and Beyond
Transition to modern RPG programming with this step-by-step guide through ILE and free-format RPG, SQL, and modernization techniques.
List Price $79.95

Now On Sale

Flexible Input, Dazzling Output with IBM i Flexible Input, Dazzling Output with IBM i
Uncover easier, more flexible ways to get data into your system, plus some methods for exporting and presenting the vital business data it contains.
List Price $79.95

Now On Sale

SQL for IBM i: A Database Modernization Guide SQL for IBM i: A Database Modernization Guide
Learn how to use SQL’s capabilities to modernize and enhance your IBM i database.
List Price $79.95

Now On Sale

BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$0.00 Raised:
$

Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: