(Author's Note: This technique came from On-Line Streaming Video RPG IV Training, where you can find more tips like this one.)
One barrier to writing subprocedures seems to be getting started with that first one. Where do you begin?
The answer to that question is to simply convert an existing subroutine to a subprocedure.
Let's use the subroutine named CENTERSR as an example of how this can be accomplished.
Consider the follow source code. It uses the subroutine CENTERSR to center the text in the field named CENTER. In this example, we copy a field whose content we want centered to the field named CENTER and then call the subroutine. After the subroutine returns, the data is copied back to the original field, presumably centered accurately, as follows:
D workfld S 255A
D center S 255A
D LeftMarg S 3P 0
D nLen S 3P 0
C eval center = myCompName
C exsr centerSR
C eval myCompName = Center
CSR CenterSR BegSR
C eval nLen = %Len(%Trim(Center))
C eval LeftMarg = %DIV(nLen : 2 )
C if leftMarg > 0
/free
%subst(workfld:leftmarg) = %TrimL(Center);
/end-free
C eval center = Workfld
C endif
CSR endCenterSR EndSR
To convert this to a subprocedure, replace the BEGSR and ENDSR statements with Subprocedure specifications, as follows:
C eval nLen = %Len(%Trim(Center))
C eval LeftMarg = %DIV(nLen : 2 )
C if leftMarg > 0
C eval %subst(workfld:leftMarg) = %TrimL(Center)
C eval center = Workfld
C endif
P CenterSR E
This creates a subprocedure starting point.
Next, convert the work fields to subprocedure parameters and local variables, as follows:
D CenterSR PI
D center 255A
D LeftMarg S 3P 0
D nLen S 3P 0
C eval nLen = %Len(%Trim(Center))
C eval LeftMarg = %DIV(nLen : 2 )
C if leftMarg > 0
C eval %subst(Center:leftMarg) = %TrimL(Center)
C endif
P CenterSR E
In the above example, the CENTER work field is converted to a parameter. The work field named WORKFLD is no longer needed. The other two fields, nLen and LeftMarg, are moved to the subprocedure. When a field is declared inside of a subprocedure, it is known as a local variable. It is not visible to the rest of the program at that point—only to the Calc specs within the subprocedure.
The last thing we need to do is create a prototype, which is a copy of the parameter list for the subprocedure. The RPG IV compiler uses the prototype to syntax-check your calls to your subprocedures. Without it, RPG IV would not be able to determine if the field you're passing on a parameter to your subprocedure should be numeric or character. So let's create a prototype for the CENTERSR subprocedure.
D center 255A
Prototypes are normally placed in the global Definition specifications near the top of the source member. It's a good idea to always put them into a /COPY member that contains prototypes for similar functions. For example, if we had procedures to left-justify text, right-justify text, center text, and search text, we might have a source member named TEXTPROTOS that contains the prototypes of all of these subprocedures.
The final step is to update the call to the subprocedure. We need to convert the call to the subroutine to a call to the subprocedure. We do that as follows:
This single line of code replaces the original Calc specs that moved, called, moved data. It also replaces the work fields we had to declare and manage. So the following has been replaced with the single CALLP operation:
D center S 255A
D LeftMarg S 3P 0
D nLen S 3P 0
C eval center = myCompName
C exsr centerSR
C eval myCompName = Center
Moving to subprocedures can be fun and exciting. Above all, it can be as easy or as complicated as you make it.
Bob Cozzi is a programmer/consultant, writer/author, and software developer of the RPG xTools, a popular add-on subprocedure library for RPG IV. His book The Modern RPG Language has been the most widely used RPG programming book for nearly two decades. He, along with others, speaks at and runs the highly-popular RPG World conference for RPG programmers.
Bob Cozzi is a programmer/consultant, writer/author, and software developer. His popular RPG xTools add-on subprocedure library for RPG IV is fast becoming a standard with RPG developers. His book The Modern RPG Language has been the most widely used RPG programming book for more than a decade. He, along with others, speaks at and produces the highly popular RPG World conference for RPG programmers.
MC Press books written by Robert Cozzi available now on the MC Press Bookstore.
 |
||
 |
|
RPG TnT Get this jam-packed resource of quick, easy-to-implement RPG tips! List Price $65.00 Now On Sale
|
|
||
 |
|
The Modern RPG IV Language Cozzi on everything RPG! What more could you want? List Price $99.95
Now On Sale
|
More 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.
TRY 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.
Forms 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.
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:
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.
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:
LATEST COMMENTS
MC Press Online