File Extension Naming

I have had a program that I created quite a while back (15 years) that used a file extension .cww which I think is now used by Codewarrior on Windows. Some years later I changed it to .cw5 which is apparently used by Codewallet. I was going to change to .cw6 in a new version but Compress Vessel uses it. Now it is unlikely that these programs will be on the same computer as my educational App but I was wondering what others do to avoid this issue? (also messes with keeping compatibility of old files)

What are the rules around who keeps or creates file extensions. If I want to create a new cross platform extension what are some good guidelines?

the big one eats the little one …

Look at Ruby extension

Use a longer extension.

Thanks, I thought as much.
While playing around with this I seemed to have removed something, my app no longer launches if I double click on a data file.
Where do i put the four letter creator code as the OS doesn’t put the right icon with the saved files either

Mac apps no longer use creator codes. You will need to familiarize yourself with Uniform Type Identifiers.

…and on Mac, you’re not limited to a 3-Char-Extension name.

Right. Linux, Windows & macOS have not been limited to 3 letter extensions for a long time. Windows since the advent of Windows NT based releases.

I have 2 file types, 1 for the Crossword Creator and one for the Crossword Player
OK so to bring my program file type up to date would it look like this?

Display Name = Crossword Wizard File
Description = ?
UTI Identifier = com.rushsoftware.cwwtext
Conforms To = public.text
Extensions = .cwwtext
Mime = ?
OS Types = ?
UTI Type = Exported


Display Name = Crossword Wizard Player File
Description = ?
UTI Identifier = com.rushsoftware.cwptext
Conforms To = public.text
Extensions = .cwptext
Mime = ?
OS Types = ?
UTI Type = Exported

Should also mention whatever I do needs to be cross platform.

The extension is the cross platform information.

You need a role, which is totally hidden in Xojo. See macOS -> FileTypes. Your role is editor. You don’t need a Mime type. Because you have a text file your OS Type should be TEXT.

There are no rules for choosing file extensions. You just have to find something that no one else has used, so searching with Google is common. As others noted, using a longer extension is fine and a good way to ensure you are unique. Xojo original started with the extension “rb” (for RealBasic), then switched to “rbp” (for RealBasicProject when Ruby stole rb from us) and now uses “xojo_binary_project” which ought to stay unique to us for a while.

You’ll set all this up in the File Type Set editor and may also need to do additional work in your installer for Windows. More information here:

That is why I wrote (earlier):

[quote=406511:@Emile Schwarz]the big one eats the little one …
Look at Ruby extension[/quote]

Thanks, working much better.