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Flexible are Your Calculations? | IBM i | IBM Systems Magazine http://www.ibmsystemsmag.com/ibmi/enewsletterexclusive/1706

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Developer> RPG

How Flexible are Your Calculations?RPG programming techniques to help you solve unsolvable problems.

September 2007 | by Jon Parisand Susan Gantner

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Well leave to your imagination what the subprocedures look like! (Or if your imagination fails you, you can study the full source code.) But before

we move on, well just show you the prototype for the calcroutine and one of the subprocedure prototypes (of necessity all of the others have the

same basic format). Notice that the calc prototype uses the EXTPROC keyword and there are no single quotation marks around the name this

indicates that currentOpPtris a procedure pointer and will determine which procedure is called. Notice also that the prototype for the add

subprocedure has exactly the same definition in terms of return value and parameters as does calc.

Adding new operations is a breeze. Simply code the new subprocedures, add the required codes to the operationsdata structure and the related

subprocedure information to the pProceduresdata structure - remembering to modify the DIM clauses of course! The main calculations wont

change at all.

So Far, So Good What Now?

We now have the mechanics in place to add as many different operations as we want. But what about referencing the variables by name? We coulduse the multi-level IF-block approach, but it has the same disadvantages as it had for the operation codes themselves. It may not be immediately

obvious, but we can adopt a similar approach for the variables to the one we used for the operation codes.

One approach we considered was to modify the subprocedures to accept pointers to the variables to be processed, but that didn't help with another

problem we needed to address namely, that when you pass a parameter, the parameter definitions in the caller and the callee must match. The

variables we want to use in our calculations probably wont be the same size and type. With a normal subprocedure, we could solve this with the

CONST or VALUE keywords. These would cause the compiler to generate the necessary code to convert the caller's variable to the size and type

required by the subprocedure. But by definition our variables will change users can select which ones to use.

Next page: >>

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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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Even More Flexible Calculations

E-Newsletter Exclusive | In the September EXTRA e-Newsletter, Jon Paris and Susan Gantner shared some solutions to &qout;unsolvable&qout;

RPG problems with a technique for flexible calculations. Now they delve deeper with a more complex example, making a sequence of calculations

not only possible but simple to create and use.

RPG - Anchoring Your Team

Cover Story | Alternate approaches to extending your RPG applications.

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