24
Sun, Nov
1 New Articles

Improve Your Passing Game Using LDA

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

The Local Data Area is a great tool for passing limited amounts of data from one program to the next. When you utilize an externally defined data structure to standardize your LDA definition, you have an extremely effective way to pass data from one program to the next. This combination can be helpful when you are trying to debug programs.

The Local Data Area, or LDA, as it is more commonly referred to, can be a powerful tool for program-to-program communications. The LDA requires very little overhead, is easy to code and maintain, and is automatically supplied with every AS/400 session. It is these very attributes which make it unique and special among the various methods of passing small amounts of information between your programs.

The data in the LDA is only available to the current job. Submitted jobs and jobs running in other workstation sessions each have their own LDAs. On the AS/400, the size of the LDA is 1K, or 1,024 bytes. You can use any or all of the LDA from any of your CL or high-level language (HLL) programs.

In addition, the LDA can be externally described in RPG programs and can be very useful in reducing (or eliminating entirely) the number of parameters that must be passed from one program to the next. This axiom is especially valuable if the data being passed needs to be accessible to only a few links within a long chain of programs. Instead of passing the same parameters from one program to the next, you can place the data in the LDA and access or update the data only in the programs that really need it.

In the case of submitted jobs, the LDA originally consists of a “snapshot” of the LDA from the workstation that submitted the job. Once the submitted job is running, however, the LDA for the submitted job takes on a life of its own. Changes to the data in the submitted job’s LDA do not affect the LDA of the job that submitted it.

Reading the Defense

Defining the LDA in your RPG programs is as simple as defining any other data structure. In Figure 1, we show the simplest definition of the LDA. The U in position 23 of the data structure definition specification (right before the DS) tells the system that we are providing a definition for the LDA.

Here, we have defined the first 43 bytes of the LDA. Even though the total size of the LDA is 1,024 bytes, the program in our example needed to define only the portion of the LDA that it was going to use. You can define subfields either by length or with “From” and “To” positions. In this example, we chose to specify the length of the subfields and let the system calculate the “From” and “To” positions for us.

Once the data is stored in the LDA, it will be available to any subsequent programs in the job.

The key to using the LDA effectively is to ensure that your definitions are consistent from program to program. It is for this reason that we recommend you define your LDA using an externally defined data structure.

What is an externally defined data structure? It is a physical file that is used for data definition instead of data storage. It is both defined with and created using DDS (exactly as you would define a physical file). In Figure 2, you can see DDS for a file used to externally define the LDA in our sample RPG program (Figure 3). If you take a look at the definition specifications, you can see where the LdaDefDS externally described data structure is used to define our LDA. The extname (external name) keyword in the DDS tells the compiler that the LdaDefDS externally described data structure should be used to describe the LDA within our program.

Externally defining the LDA has two major advantages:
1) There will be a consistent definition of the LDA from one program to the next. This will help you to avoid data decimal errors, field-name inconsistencies, and other annoying program termination errors.

2) Changing the definition of the LDA is as simple as changing the definition specifications of the externally defined data structure and recompiling the programs that reference the LDA. Obviously, the programs that need the new definition would need to be changed too, but the process is simplified.

There are a variety of OS/400 commands that are designed to work with data areas. A few of them were designed to work with the LDA, too. These are the Change Data Area (CHGDTAARA), (Display Data Area) DSPDTAARA, and Retrieve Data Area (RTVDTAARA) commands. You simply need to use *LDA as the first positional parameter or enter *LDA when prompted for the data area name.

Watch Out for the Blitz!

The RPG program prompts an operator for parameters required to run a report. (The prompt display is shown in Figure 4.) The operator is required to enter a range of transaction dates, as well as some additional options regarding the printed output. The program edits the entries for validity and issues any errors found. Once the entries are deemed to be error free, the LDA is updated, and the report program (named REPORTCL) is submitted to the job queue.

The first thing the RPG program does is read in the LDA (using the IN op code) and clears all current contents. We do not want whatever happens to be there to interfere with the operation of our report prompt program. We then call a simple CL program that retrieves the operator default printer ID and Output Queue names via the Retrieve Job Attributes (RTVJOBA) command. The retrieved values will be presented on the prompt screen as default values.

The program then establishes a loop that will present the prompt screen and perform an edit on the values entered. If the values entered are valid, the program writes the values out to the LDA using the OUT op code. The REPORTCL program will then be submitted to the job queue. If errors are found, they will be presented on the screen. The operator will remain in the loop until valid entries are keyed and the report is submitted, or the operator presses the F3 function key to exit.

We should note that the IN and OUT op codes in our RPG program were necessary only because we needed to read and write the contents of the LDA outside of the program

cycle. We could have omitted the op codes if we wanted the LDA read at program initialization and written at program termination.

Since the LDA of a submitted job is initially the same as that of the submitting job, the LDA established in our report prompt program is available to any program called within the submitted REPORTCL job.

Look for the Open Man

Submitted jobs can sometimes be a real pain to debug. That is not the case with our submitted REPORTCL job. Why? Because by simply using the DSPDTAARA command (with *LDA as the primary positional parameter), you can see the parameters that were submitted with the job.

The other reason it is easy to debug a program using the LDA is that you may now run the submitted job (REPORTCL, in our case) interactively. Since the data required in order for the report to run is stored in the LDA, we do not have to hassle with the parameters which would normally need to be passed to our called program. If we need to change one of the parameters for our test, we simply use the CHGDTAARA command to do so.

First Down!

When you combine the use of two pretty good tools, like the LDA and externally described data structures, you can end up with results that exceed expectations. In this particular case, we ended up with code that was easier to understand, debug, and maintain. Hopefully, this will allow us more time to work on the projects we would prefer to work on.

Figure 1: Program-described definition specifications defining the LDA Figure 2: Externally described data structure used to define the LDA

DName+++++++++++ETDsFrom+++To/L+++IDc.Keywords
D LDA UDS
D DeviceID 10
D OutQueue 10
D Copies 3S 0
D DateFrom L
D DateTo L A R LDAREC TEXT('Local Data Area Desc')
A DEVICEID 10A TEXT('Printer ID')
A OUTQUEUE 10A TEXT('Name of OutQueue')
A COPIES 3S 0 TEXT('Number of Copies')
A DATEFROM L TEXT('Report "From" Date')
A DATETO L TEXT('Report "To" Date')

FLDA001Ds cf e workstn

D Command s 512
D Length s 15 5 *

d Lda euds extname(LdaDefDS)

c *dtaara define *lda Lda
c in Lda
c clear Lda
c eval Copies = 1 * retrieve USER ID default values for Printer ID and OutQ
c call 'LDA001CL'
c parm DeviceID
c parm OutQueue

c dou *InKc
c exfmt prompt * clear error indicators
c movea '0000000' *in(40) * eoj requested
c if *InKc
c leave
c endif * edit format entries
c *mdy test(d) FromDate 41
c *mdy test(d) ToDate 42 * "from" date must be less than "to" date
c if *in41 = *off and *in42 = *off
c *mdy move FromDate DateFrom
c *mdy move ToDate DateTo
c if DateFrom > DateTo
c eval *In43 = *On
c endif
c endif * must specify a printer and the number of copies
c DeviceID comp *blanks 44
c Outqueue comp *blanks 46
c Copies comp *zeros 45 * if any errors are found, set the alarm and re-submit display
c if *in41 or *in42 or *in43 or *in44 or
c *in45 or *in46
c eval *in40 = *on
c iter
c endif * free of errors, so submit report

* Write LDA
c out Lda * Submit report to the job queue
c eval command = 'sbmjob cmd(+
c CALL PGM(REPORTCL))'
c call 'QCMDEXC'
c parm command
c parm 28 length
c leave
c enddo
c eval *inlr = *on

Figure 3: RPG Report Prompt program

<>
<>
<>

Figure 4: Sample Report Prompt screen



Improve_Your_Passing_Game_Using_LDA05-00.png 897x512
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: