04
Mon, Nov
1 New Articles
  1. You are here:  
  2. Home
  3. Programming
  4. RPG
  5. Reader Feedback and Q&A

Reader Feedback and Q&A

RPG
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times
I am beginning to receive questions and comments regarding previous issues' content as well as questions on entirely new topics. To that end, I am starting a Reader Feedback and Q&A section. I will include this section as part of an issue when you send me feedback or questions that warrant publication. While other publications may print questions that are fabricated to suit the purposes of the publication, I will only answer questions you send me through email, online forums, or my RPG IV list server. So keep in touch!

Q: I recently discovered an API named "Access" in a published article. I copied the syntax into my program. It works and saves me a lot of time. I have no problem with this as long as I understand what is going on. I have researched the Access API and understand the parameters, but there is one part of the following line of code that I have not seen before.
     C                   return    (Access(%Addr(Filename):F_OK) = 0)


The part I do not understand is the use of = 0. I suspect it has more to do with calling a procedure than the Access API. Can you help me with this?

A: I don't know where you found the Access() API/procedure you mention, but the technique used in your example code is a technique that I teach in my onsite RPG IV seminars.

It is what we call a "Boolean expression," meaning that the result of the expression is either true or false (*ON or *OFF in RPG IV-speak). In your example, the value returned from the procedure is compared to zero. If the returned value is equal to zero, then the condition is true and *ON is returned to the caller. If the return value is not equal to zero, then the condition is false and *OFF is returned to the caller.

A similar Boolean operation, one that I use in my seminars, follows:

     C                   eval      *INLR = (A = B)


In this expression, if A is equal to B, then *ON is moved into *INLR; otherwise, *OFF is moved into *INLR.

The conditional expression on the right side of the assignment operator (i.e., the equal sign) is performed as though it were on an IF statement. The result of the conditional test is copied to the field on the left side of the assignment operator. The Boolean expression illustrated above could be rewritten as follows:

     C                   if        A = B
     C                   eval      *INLR = *ON
     C                   else
     C                   eval      *INLR = *OFF
     C                   endif


If you're a long-time RPG programmer, you may remember the COMP (compare) operation code. The COMP operation code compared two values and set on an indicator based on the result of that comparison. Boolean expressions in RPG IV can be thought of as a contemporary form of the COMP operation code.

Remember, however, that an indicator data type was added to RPG IV a few releases back. So the result of a Boolean expression can be either a traditional RPG indicator or a so-called named indicator. The data type for named indicators is N, and the fields must be one position in length. Here's a simple named indicator being used in the same situation:

0001 D match           S              1N   Inz(*OFF)

0002 C                   Eval      match = (A = B)


The MATCH field (line 1) is declared as a named indicator (N data type) and is initialized to *OFF. Line 2 does a comparison of A equal to B, and if A is equal to B, *ON is moved into MATCH; otherwise, *OFF is moved into MATCH.

BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$

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: