Re: Dynamic Variable Names in RPGLE -- RPG400-L

Any idea if we can use dynamic variable names in RPGLE?

Something like this
fldvalue = %value(&var1);

What you have to understand is that computers don't understand variables.(Not directly, anyway.) When a program is running, it has no notion ofvariables, it just has addresses in memory.

"Read 4 bytes from address x'123456' and store that in aregister. Read 4 bytes from address x'654321' and store that in aregister. Add the two registers together. Store the result in memorylocation x'987654' and so on...

There are no variables. Variables are a device that was created to makelife simpler for human beings to write computer programs.

Now, an interpreted language (one that isn't compiled) has variables atrun time, because the source code is being translated as the program runs.In an interpreted language, it's relatively easy to have something likevarName = 'custno'; varValue = %value(varName). Why? Because it's inthe process of interpreting the source code and converting variables intomemory addresses ANYWAY... it's no problem for it to do that dynamically.

On the other hand, for a compiled language like RPG, there are novariables anymore. They were discarded when the program was compiled.None of the variable names exist anymore. (with a few exceptions)

Once we chain to a file or create cursor program knows what fields are
available.  Is there any API or Userspace stuff to get the value of the
fields using a dynamic variable name?

Yes and no. One situation where the variable names are stored in theprogram code is when you have a DBGVIEW() specified. In that case, thevariable names are saved in the program so that you can refer to them whenyou're debugging. Consequently, the debugger APIs would be able to dowhat you're asking for.

Another situation is when a variable is exported from service program. Inthat case, the variable's name is made available so that any other(separately compiled) program is able to look up the memory location basedon the export name. For that, you can use the QleGetExp() API to get apointer to the export.

For an externally defined file, you may be able to derive the field valuebased on the field name because the name is part of the file's externaldefinition. If the fields are loaded from the file into contiguous memory(such as when you use a data structure to load the fields into) then youcould use the field's offset in the record as the offset from the start ofthe user space to set a pointer to the spot where the field lives inmemory.

But, other than those times, there's really no way to do what you'reproposing, other than re-design RPG from the ground up as an interpretedlanguage.

If you tell us why you need this capability, I'm sure we'll havealternatative ways of solving your problem that don't involve this levelof complexity.