Recently, I had to write a program that displayed two identical files residing in two different libraries. I wanted to display the data side by side, but presenting two subfiles horizontally wasn't user-friendly enough and made for a lengthy program. I came up with a technique that works similarly to side-by-side subfiles, but it's easier for the user and easier to program.

Define a subfile with the fields you need to see, keeping fields from one file in one half and fields from the other file in the other half. Load the subfile a page at a time. Initially, load the subfile from both files. Use the cursor position returned through the file information data structure (INFDS) to detect which half of the screen the user is in. Update only the fields for the file belonging to the half of the screen where the cursor is located. (Use the CHAIN and UPDAT operation on the subfile because you will be changing the records already in the subfile.)

The page-at-a-time technique I used allowed me to save the key from the first record on each page in an array and use that key to reset the file pointer for each roll up or roll down request.

This technique works great. Use it any time you need to present two lists side by side without using two subfiles.

-Michael Veit