Re: Dynamic sized multiple occurrence data structure -- RPG400-L

Hi Mike,

Is there any trick available to create a multiple occurrence data
structure and define the size at run time?

[SNIP]

my application is used as a stored procedure that returns a result setand so I can't use arrays.

The "SET RESULT SET" SQL statement can specify the number of rows toreturn. For example


     C/exec sql Set Result Sets Array :MYMODS for :COUNT Rows
     C/end-exec

Your program will have to keep track of how many elements you've loadedinto the MODS and set the number of rows (in the COUNT variable in myexample, above) appropriately.

As far as how many occurrences exist in your MODS, I strongly recommendthat you allocate all 1000 of them as a normal MODS. The unususedoccurrences won't matter. The amount of memory they occupy won't have anysignificant impact on the system.

It's possible to base your MODS on a pointer, and allocate only as many asyou need -- exactly the same way you do it with an array -- but there'sreally no value to doing so (either with a MODS or an array!) if you onlyhave 1000 elements.

You can hurt the performance of your program, and make a program that'svery difficult to maintain, using techniques like this. Sure, you maysave a few kilobytes or even megabytes of memory, but who the heck caresabout that? The iSeries will store unused portions of your program ondisk, only loading it into memory if nothing else needs the memory. Sothe amount of memory you use really doesn't have a sigificant impact.Certainly nothing worth the cost of making your program hard to maintain!!

Even if the memory usage is a problem, big deal. Buy another 512mb memorymodule for your system. What does that cost? $300 or something? Bycomparison to the extra days it'll take you to write and debug yoruprogram, and by comparison to the years of extra time maintaining yourprogram, the cost of an extra memory module is extremely cheap. Don'tcreate a maintenance nightmare over a couple of kilobytes!