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RPG Academy: BIF Up Your Code! Part 4, Simplifying String Operations with BIFs

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You can simplify your code with the set of string-related BIFs presented in this TechTip. Master them and you'll be the one pulling the strings of your code and not the other way around.

 

Working with strings in RPG can be a real pain: all of those MOVE and CAT op codes and work variables with different lengths just to "stitch" the appropriate string together!

 

Don't take this the wrong way, but using MOVE and CAT to handle strings is so System/36! Over the years, IBM introduced several time-saving BIFs to handle almost every situation when it comes to string operations. In the previous TechTip, I introduced %CHAR and you probably already know %TRIM, but there's still a lot more to discover.

 

"Old" vs. "New" Ways

The code below depicts the old, "traditional" and the new, "BIF-esque" ways of performing a few string operations. Both scenarios perform the same task: splitting a string in two, adding some text in the middle, and stitching them back together. Let's start with the "traditional" approach:

 

D base_str       S            100A   INZ('THIS IS A TEST, 1, 2, 3')

D result         S           100A   INZ(*BLANKS)      

D temp_str1       S             15A   INZ(*BLANKS)

D temp_str2       S             84A   INZ(*BLANKS)    

D temp_str3       S             19A   INZ(*BLANKS)    

                                                              

C                   MOVEL     base_str     temp_str1    

* "temp_str1" is now 'THIS IS A TEST,'                      

C                   MOVE     base_str     temp_str2      

* "temp_str2" is now '1, 2, 3'

* plus a lot of trailing blanks that I'm omitting

C     temp_str1     CAT       ' 0,'         temp_str3      

* "temp_str3" is now 'THIS IS A TEST, 0,'              

C     temp_str3     CAT       temp_str2     result        

* "result" is now 'THIS IS A TEST, 0, 1, 2, 3'

* plus a lot of trailing blanks that I'm omitting

 

 

Now for the new, "BIF-esque" approach:

 

D base_str       S           100A   INZ('THIS IS A TEST, 1, 2, 3')

D result         S           100A   INZ(*BLANKS)                  

D temp_str1       S             15A   INZ(*BLANKS)                  

D temp_str2       S             84A   INZ(*BLANKS)                  

D temp_str3       S             19A   INZ(*BLANKS)                  

                                                                      

C                   EVAL     temp_str1 = %SUBST(base_str : 1 : 15)  

* "temp_str1" is now 'THIS IS A TEST,'                              

C                   EVAL     temp_str2 = %TRIM(%SUBST(base_str : 16))

* "temp_str2" is now '1, 2, 3'                                      

* without the %TRIM, it would be ' 1, 2, 3'                        

C                   EVAL     temp_str3 = temp_str1 + ' 0, '        

* "temp_str3" is now 'THIS IS A TEST, 0, '                          

C                   EVAL     result = temp_str3 + temp_str2        

* "result" is now 'THIS IS A TEST, 0, 1, 2, 3'                      

 

 

However, thanks to the EVAL op code and the BIFs, this could be much shorter.

 

In fact, it can be written in only one statement:

                                        

(…)

C                   EVAL     result = %SUBST(base_str : 1 : 15)

C                                         + ' 0, '        

C                                        + %TRIM(%SUBST(base_str :

16))  

 

 

This is an "over the top" example, but surely you see the difference in readability and maintainability between the two scenarios: while the variable sizes are critical to the success of the MOVE and MOVEL operations, in the "BIF-esque" approach they are irrelevant, as long as they're big enough to hold the substrings they need to hold. Even if you're familiar with the BIFs used here, keep reading. You might find something that you didn't know about these BIFs.

 

 

 

Out with the Old, in with the New

 

Let's begin with %SUBST. This BIF is similar to the SUBST op code (which I could have used in the "traditional" approach instead of the MOVE op code, but chose not to), with the same three parameters: base string, start position, and length to extract. Actually, the SUBST op code has a fourth parameter (the target string), which doesn't exist in its BIF counterpart due to its function nature. Anyway, if the third parameter is not specified, the length is the length of the string parameter less the start value plus one. In other words, the start position and everything to its right will be extracted, as you can see from the temp_str2 assignment in the code above. If you're still a bit confused, here are a few simple examples to make things clearer:

 

  • The value of %SUBST('Hello World' : 7) is 'World'
  • The value of %SUBST('Hello World' : 5+2 : 10-7) is 'Wor'
  • The value of % SUBST('abcd' + 'efgh' : 4 : 3) is 'def'

The first example, which omits the length parameter, returns everything to the right of position 7, including that character (see temp_str2's assignment above); the second one uses all three parameters and also illustrates the use of arithmetic operations in the start position and length parameters; you'll see how useful this can be later (see temp_str1's assignment above); finally, the third example shows a concatenation operation in the base string parameter; even though this might not be very common, its purpose here is to remind you that the CAT op code can be replaced by the '+' operator and used to simplify string concatenation (see temp_str3's and result's assignment above).

 

Do You %TRIM?

If you already knew %SUBST, it's possible that you also know %TRIM and its siblings, %TRIMR and %TRIML. What you might not know is that you can also use %TRIM to…well, trim characters other than the blank space. To do that, you just need to specify the characters to trim in the BIF's second (and optional) parameter:

 

 

D edited         S             20A   INZ('£******1.23***      ')

 

D trimmed         S             20A   Varying

 

 

 

C                   EVAL     trimmed = %TRIM(edited : '$£*')

 

 * Trims '£' and '*' from the edited numeric value     

 

 * "trimmed" is now '1.23***     '     

 

However, note that blanks will not be trimmed, since a blank is not specified in the 'characters to trim' parameter. To do that, you need to add a blank space to the second parameter of the BIF, like so:

 

D edited         S             20A   INZ('£******1.23***     ')
D trimmed         S            20A   Varying
 
C                   EVAL     trimmed = %TRIM(edited : '$£* ')
 * Trims '£', '*' and ' ' from the edited numeric value     
 * "trimmed" is now '1.23'

It's possible to do the same with the aforementioned %TRIML (Trim leading characters) and %TRIMR (Trim trailing characters), but it will 
only affect the characters to the left and right of the edited number from the example above, like this:

D edited         S             20A   INZ('£******1.23***     ')
D Ltrimmed       S             20A   Varying
D Rtrimmed       S             20A   Varying
 
C                   EVAL     Ltrimmed = %TRIML(edited : '$£* ')
 * "Ltrimmed" is now '1.23***       '
C                   EVAL     Rtrimmed = %TRIMR(edited : '$£* ')

* "Rtrimmed" is now '£******1.23'

 

By using BIFs as parameters to other BIFs, it gets easy to shorten the number of lines of code, but don't get carried away! It's crucial that you keep a sane balance between number of lines and readability.

 

Finally, you could argue that there are ways to determine the exact position of a substring within a string; finding the 'TEST, ' substring in the example above can be performed with the SCAN op code. That's correct, and it will be discussed in the next TechTip. Meanwhile, comment away in the Comments section below!

 

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

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