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Administrator > Security

An Array of Arrays

July 2006 | by Jon Paris and Susan Gantner

Print Email

An Array of Arrays

One of the most under-utilized features of RPG IV has to be arrays. We frequently see programs that use a database lookup when an array could've

served the purpose and would almost certainly have been far more efficient. For example, many of you probably have a database on your system

containing the U.S. state codes and names. This, in spite of the fact that the last record to be added to the file was Hawaii in August of 1959. Not

exactly a dynamic file is it?! We suspect that part of the reason for this lies in the fact that prior to V5R1, RPG didn't have a high-speed array search

capability. The performance of the old LOOKUP op-code was so poor that it was often faster to use a database lookup. The advent of the %LOOKUP

BIF removed this shortcoming, but old habits die hard. If you want to know more about the details behind how %LOOKUP operates read the article,

"Look before you %LOOKUP."

For this article, we decided to explore the idea of using arrays for the validation of codes such as account and part numbers, GL codes, etc. Our

examples demonstrate two basic approaches to the problem. The first method searches a conventional RPG array, which is loaded with all of the

customer numbers present in the customer master file. The second takes a rather different approach. It takes advantage of the fact that customer

numbers are indeed numbers and uses the number as the index into an array of indicators. The programs have been set up to time their operation

through a number of iterations so we can compare the relative speeds of the different approaches. It may have occurred to you since both of these

approaches utilize arrays, that they're constrained by RPG's limit of 32,767 elements. We'll address that issue in our third example.

Now that you know where we're headed, let's jump into our first program.

H Option(*SrcStmt:*NoDebugIO) DftActGrp(*No)

H BndDir('PARIS/EXTRATOOLS')

FcustMast IF E K DISK

/Copy BASETOOLPR

D LoadCustomerNumbers...

D pr 10i 0

(A) D validCustomer s Like(custNo)

D Dim(32767) Ascend

D customerCount s 10i 0

D searchCust s Like(custNo)

D x s 10i 0

D result s 10i 0

D loopMax s 10i 0

D hits s 10i 0


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D misses s 10i 0

D splitTimestamp ds

D timestamp z

D timePortion 12a Overlay(timestamp: 12)

/Free

(B) dsply 'Number of test loops to run?' '' loopMax;

StartTimer();

customerCount = LoadCustomerNumbers();

For x = 1 to loopMax;

searchCust = GetRandom( 1: 32000 );

i = %Lookup(searchCust: validCustomer: 1: customerCount);

if i > 0;

hits += 1;

else;

misses += 1;

endIf;

endFor;

(C) timestamp = StopTimer();

dsply ('Total time ' + timePortion );

dsply ('Hits = ' + %Char(hits) + ' - Misses = ' + Char(misses) );

*inlr = *On;

/end-free

(D) P LoadCustomerNumbers...

P b

D pi 10i 0

/Free

read custMast;

Dow not %Eof( custmast );

customerCount += 1;

validCustomer( customerCount ) = custNo;

read custMast;

EndDo;

return customerCount;

/end-free

P LoadCustomerNumbers...

P e

Next page: >>

Page 1 2 3

Jon Paris is a technical editor with IBM Systems Magazine and co-owner of Partner400.

More Articles From Jon Paris

Susan Gantner is a technical editor with IBM Systems Magazine and co-owner of Partner400.

More Articles From Susan Gantner

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