For decades, the LOOKUP opcode has been the operation of choice for searching an array for a specific value. In addition, the LOOKUP opcode provides methods for searching for values that are greater than, less than, or equal to a specific value. There's no new news there.
In OS/400 V5R1, IBM introduced the %LOOKUP built-in function. Unlike most opcodes that have been ported to a built-in function, however, %LOOKUP actually has additional function. %LOOKUP not only allows you to specify the starting array element for the search, it allows you to specify the number of elements to be searched. Finally, we can search from element 3 to element 7 without an act of Congress!
Like the %TRIM built-in function, %LOOKUP comes in multiple versions. With the LOOKUP opcode, the now-deprecated Resulting Indicators controlled the type of search being performed. You could specify up to two resulting indicators to combine up to two search types. For example, you could search for a value of greater than, a value of greater than or equal to, a value of less than, a value of less than or equal to, and so on.
The built-in function simplifies this control by providing %LOOKUPxx where xx is a Boolean control. Currently, there are LT, LE, GT, and GE Boolean controls and therefore a total of five lookup built-in functions; using %LOOKUP without any "xx" suffix causes a LookUp equal condition. I have to admit that I spent about 30 minutes trying to figure out why %LOOKUPEQ did not compile, and then I opened The Modern RPG IV Language and realized that the equal look up is spelled %LOOKUP not %LOOKUPEQ.
The LookUp built-in functions are as follows:
- %LOOKUP(SearchText : Array [: StartIndex [: NumElems]])
- %LOOKUPLT(SearchText : Array [: StartIndex [: NumElems]])
- %LOOKUPLE(SearchText : Array [: StartIndex [: NumElems]])
- %LOOKUPGT(SearchText : Array [: StartIndex [: NumElems]])
- %LOOKUPGE(SearchText : Array [: StartIndex [: NumElems]])
Here is an example of %LOOKUP being used:
D nState S 5I 0
C eval nState = %lookup('IL' : States)
Of course, you don't need to do a SORTA before a %LOOKUP built-in function. However, if you want to use %LOOKUPxx and search for a greater than, less than, or similar condition, then the array must previously have been sorted or arranged in ascending or descending sequence.
%LOOKUPxx returns the array element where it locates the search text. If you need to begin the search in another location, you specify the starting array element on the third parameter of %LOOKUPxx,
In addition to LOOKUP, there is also a C language runtime function named bsearch() that allows you to search for a pattern not only in an array but in any character string. While similar to the %scan() built-in, bsearch() is really intended for searching through an array of data for a specific value. The interesting thing is that with bsearch() you have to write a compare routine (i.e., subprocedure) that bsearch() will call to do the comparison.
For now, the power of %LOOKUPxx provides you with all the search capability you need for arrays. In the future, enhancements to LOOKUP may include the abilities to search multiple-occurrence data structures and to specify the data structure subfield on which to perform the lookup. I'm looking forward to that enhancement!
Bob Cozzi has been programming in RPG since 1978. Since then, he has written many articles and several books, including The Modern RPG Language--the most widely used RPG reference manual in the world. Bob is also a very popular speaker at industry events such as RPG World and is the author of his own Web site and of the RPG ToolKit, an add-on library for RPG IV programmers.