Re: Passing Files as Parameters

Comments in-line

Jon Paris

www.Partner400.com
www.SystemiDeveloper.com



On Nov 4, 2010, at 9:48 AM, rpg400-l-request@xxxxxxxxxxxx wrote:

Would that be that it permits having all file operations in the callee? With the file having to be declared in both caller and callee, I don't really get the advantage.

1) It avoids the file being opened multiple times (file open is relatively expensive)

2) It makes it possible to write more generic routines for file handling (think subfiles for example) that take advantage of the fact that the current cursor position comes "with" the file.

There are a bunch more but these are the main ones. Like a lot of new functionality the usage is not always immediately apparent, becuase we've got used to building things a certain way. We tend to constrain our designs to fit the mental set of "tools" that we have. If you were to reverse the scenario and ask a C programmer (for example) how they would design an application in a scenario where they could _not_ pass files as parms they would be astounded that you could even contemplate such a restrictive scenario.

Also, WHAT exactly is being passed as the first parameter? Why is the file template not in the caller instead of the callee? What's the advantage over declaring the files in both caller and callee and passing only 2 parameters, the key and the record? Thanks!

What is passed? Nothing that is of any use to you other than for its intended purpose. It is an internal reference to the associated entries in the RPG run-time. Think c-style file handle. The file itself has to be defined (and is "owned") by the first program in the chain. Any subsequent program/procedure in the chain needs to know what the file looks like hence the need for the template. The advantage as I've already noted is that only one open is done.