13
Sat, Jul
4 New Articles

RPG Academy: BIF Up Your Code! Using BIFs to Perform Date Operations

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

RPG's date-related BIFs form a powerful set of tools that will help ease your date-operations-caused pains! Keep reading to learn how to use them properly.

 

Date operations, such as calculating a due date or something apparently as simple as retrieving the last day of a given month, are the source of many headaches for RPG programmers everywhere.

 

Everyone has a few homegrown date routines in their applications. Even though they work well most of the time, they become a nightmare when they don't do what we expect. RPG has a well-balanced set of BIFs to handle date, time, and timestamp data types, and you can use them to replace those error-prone, ages-old code, thus making your code clearer, faster, and more reliable. Let's start with the date-related BIFs and leave the time/timestamp BIFs for later.

 

A Simple Problem: Calculating the Last Day of the Month

What seems to be a simple problem can sometimes be a big chore. Calculating the last day of the month is a common date operation that many of us have in our applications. Most solutions I've seen use a compile time array and do some math to determine the last day of February. To be honest, most implementations of this date operation work well and don't need replacing (surely there are more urgent situations to address), but I chose to use this as an example because it's a very common situation.

 

I'm going to build a function that returns the last day of the input date. For that, I'll use a Date variable as input parameter and return a two-digits-long packed decimal. You might say, "OK, that's a problem for me because my dates are all stored in decimal (8, 0) format." To that, I say, "Not a problem; just use a BIF to convert them to Date format." That's where I'm going to start.

 

Introducing the %DATE BIF

In two recent TechTips (1 and 2), I explained how to use BIFs to convert between numeric and character data types. Some readers commented that I had forgotten about %DATE, but it wasn't a lapse; it was a conscious attempt not to overwhelm the readers with information. Anyway, the time has come to introduce %DATE. This BIF takes character, numeric, or timestamp expression data and converts it into a date data type. There's a second, optional parameter to indicate the date format of the expression. If the date format is not specified for character or numeric input, the default value is either the format specified on the DATFMT control-specification keyword or *ISO. Here are some examples of the %DATE BIF usage:

 

D W_ValidDate   S               D   INZ

(…)

C                   EVAL     W_ValidDate = %Date('2014-11-16')

C                   EVAL     W_ValidDate = %Date(20141116)  

  

This, however, will produce an error, because the date is not valid:

 

C                   EVAL     W_ValidDate = %Date('2014-31-99')

 

This will cause a compile time error because the expression can be evaluated at compile time. If instead of the literal I had a variable as %DATE's input parameter, then the error would occur at run time.

 

Now that we know how to convert the numeric and character fields to date, we can provide the input that the LastDayOfMonth function expects. So let's build it!

 

The LastDayOfMonth Function

As I said before, this function takes in a date and returns the last day of that date's month. There are many (creative) ways to calculate the last day of a given month, so feel free to use whatever you prefer. The one I present here was engineered to make use of a few more date-related BIFs, as you'll see in a moment. Let's start with the function prototype, work variables, and input parameter validation:

 

*------------------------------------------------------------------------*

*   Copy Statements                                                     *

*------------------------------------------------------------------------*

* Date Operations                                                        

/Copy QCPYLESRC,DTE_OPS_PR                                              

                                                                          

*------------------------------------------------------------------------*

*   Last day of the month (returns the last day of the month of a date) *

*------------------------------------------------------------------------*

P LastDayOfMonth B                  Export                              

D LastDayOfMonth PI             2P 0                                    

* Input parameters                                                      

D P_Date                         D   VALUE                        

                                                                          

* Work variables                                                        

D W_Return       S             2P 0 INZ(99)                            

D W_Date        S               D   INZ                                

D W_TempDate    S               D   INZ

                                                                          

* Check input parms                                                      

* P_Date                                                                  

C                   TEST(E)                 P_Date                        

C                   IF       %ERROR                                      

C                   RETURN   W_Return                                    

C                   ENDIF                                                

 

This first part of this code, right down to the input parameter validation, is very similar to the Chg_Case function's from two previous TechTips (1 and 2), so I won't go over it in detail. Notice, however, that I'm using the TEST opcode with the (E) extender to test if the input parameter contains a valid date. The extender allows me to do without yet another indicator and use the %ERROR BIF instead. I'll talk more about this BIF when I discuss error handling, later in the series. Anyway, if P_Date doesn't contain a valid date, 99 (the value to which W_Return is being initialized) is returned. It's a simple way to indicate an error, because 99 is definitely not a valid last of the month. Now let's skip to the calculation itself, since there's no need to retrieve additional information (remember the three-step process of building a function introduced before?). I'm going to calculate the last day of the month by first finding the last day of the previous month, adding a month to the resulting date and then extracting the day of that date. For that, I'll use the %DAYS%MONTHS, and %SUBDT BIFs. While the first two are straightforward (they convert a numeric value to a "Date-type-operation-compatible" format), %SUBDT is a bit more complex; think of it as a kind of %SUBST for dates, where you indicate the part of the date you want to extract instead of the starting character. While the first two are straightforward (they convert a numeric value to a "Date-type-operation-compatible" format), %SUBDT is a bit more complex; think of it as a kind of %SUBST for dates, where you indicate the part of the date you want to extract instead of the starting character. Look at the code below, and all of this will become clearer:

 

* If the input parm is ok, calculate the last day of the month          

* by adding a month and then subtracting the day part of that date,

* from the itself, to get the last day of the input date's month

C                  EVAL     W_TempDate = P_Date + %Months(1)               

C                  EVAL     W_Date = W_TempDate

C                                   - %Days(%SubDt(W_TempDate: *Days))

* Return the last day of the month                                      

C                   EVAL     W_Return = %SUBDT(W_Date:*D)                

C                   RETURN   W_Return                                    

                                                                          

P LastDayOfMonth E                                                      

 

There are two steps to the process: calculate the last day of the month by first adding a month to the original date – W_TempDate = P_Date + %Months(1) – and then subtract the day part of this temporary date to find the last day of the previous month – W_Date = W_TempDate - %Days(%SubDt(W_TempDate: *Days)). So there you have it —20 something lines of code, including comments and the function's header and footer, that solve a simple problem in a simple way.

 

Two things that I haven't mentioned: there's also a %YEARS BIF that works just like %DAYS and %MONTHS; and %SUBDT can be used to extract any of the three date components by specifying *DAYS*MONTHS, or *YEARS or their short versions (*D, *M, or *Y, respectively) in the BIF's second parameter. The readers with SQL experience are probably wondering why use RPG for this if there's an SQL function that does the same thing. Well, you're right: I'll be talking about the Last_Day SQL function in a future TechTip of the SQL 101 Series.

 

As I said in the beginning, the date-related BIFs are very powerful and useful. The next TechTip will demonstrate just that by doing some more "date math" with %DIFF. Until then, I want to hear from you: use the Comments section below (or the usual LinkedIn groups) to leave your comments and questions!

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: