Re: pointer arguments in procedures -- RPG400-L

What I don't understand is how, inside the procedure, to make RPG
understand that the pointer is a string pointer so that I can do %subst
and all the other usual string operations on the argument.

Pass an actual STRING to the procedure. Pass it by reference (rather thanby VALUE) so that all that gets passed under the covers is the address ofthe variable. Then you don't need to work with pointers at all, andyou'll be able to use string operations on it.

If you want any size variable to be used as input, add options(*varsize)to the prototype, and it'll allow any size variable to be passed.However, if you do that, be very careful not to refer to the memory beyondwhat the caller passed in, or you'll be looking at memory that doesn'tbelong to you.

RPG does not have data types for pointers, as C does. I think you'reprobably coming from a C background, because it (and C++) are the onlylanguages I know of that have the peculiar notion that a pointer shouldhave a data type. A pointer is exactly that -- a pointer. It's avariable that holds an address.

IMHO, what scares people away from working with pointers is the complexityof using them in C where they're not just pointers, but also specify aview of memory... then you get into things like casting pointers to otherpointers, or dereferencing a pointer that the pointer points to... it getsvery complicated very quickly in C... and people get scared.

Pointers in RPG are much simpler. They're just variables holding anaddress. That's it. If you want to view what's at that location inmemory, you declare a variable that's based on that pointer -- then thatvariable uses the memory that the pointer points to. Very simple.

But all of this is unnecessary for what you want to do -- all you need todo is pass the character field by reference. You don't need pointers orbased variables.

Unless, of course, you're trying to implement your own "string class" thatallows more than 64k of data in a character variable. If you're doingthat, then you'll have to use BASED and pointers -- but I'd recommend NOTusing RPG's string opcodes in that case. I'd also recommend adding alevel of abstraction so that the caller doesn't know that he has to pass apointer, instead of that have some sort of "String Data Type" that getspassed.