File Associations

• User: HKCU\Software\Classes

• System: HKLM\Software\Classes

• Old Way: HKCR\

  • I recently learned HKCR had actually been obsoleted a decade ago (I forget if it was Win95 or WinXP)
    https://social.msdn.microsoft.com/Forums/vstudio/en-US/630ed1d9-73f1-4cc0-bc84-04f29cffc13b/what-registry-keys-are-responsible-for-file-extension-association?forum=netfxbcl

• File Extension: HKCU\Software\Classes\.ext\

  • (Default) = NameOfAssociation (ie, PerlScript or txtfile, etc)
  • PerceivedType = text (or similar)
  • ShellNew\
    • see Customized Context Menu (not included)

• Association: HKCU\Software\Classes\NameOfAssociation

  • (Default) = Text Version of Name of Association (shown in Explorer)
  • DefaultIcon\(DEFAULT) = PathToIcon
  • Shell\
    • (Default) = nameOfVerb (sets the default verb to run for double-click)
    • nameOfVerb\
      • (Default) = Human Readable Verb
      • command\(Default) = path\to\exe "%1" %*
        • make it REG_EXPAND_SZ if you want path to include %EnvironmentVariables%

• RClick > “Open With” > Use as Default end up here: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\

  • reference: https://stackoverflow.com/a/3924822/5508606
  • If you want to go back to the system default, delete ...\FileExts\.ext\UserChoice

I’m wondering the best way to undo the weird changes done to my registry

If you had used a registry-watcher utility to see exactly what changes Notepad++ made, it would be easy.

In the “good old days” of Windows, where they always used HKCR (or, technically, it’s been using that as an alias to the appropriate sections of HKCU\Software\Classes for user-specific associations and HKLM\Software\Classes for system-level associations), I would have just gone through the .ext entries, and looked up their FileType entries, and modified or deleted those shell commands. However, the “always use this app to open” settings in modern Windows will sometimes use different or convoluted registry entries, and I don’t always know where to look for those. That’s why when I am playing with associations, I prefer to just use the registry directly, and avoid both in-app and windows-gui association manipulations. Unfortunately, MS is fighting harder against that, and I’ve started to see sometimes where MS resets the app that gets used, even though my HK**\Software\Classes settings have remained unchanged; I’m still trying to figure out exactly how MS does the modern “default app” settings.

Or, the TL;DR version: good luck with that. :-)

But of course now I realize I really don’t want these file associations at all, and I’m wondering the best way to undo the weird changes done to my registry from what I attempted inside of Notepad++.

So I’m flummoxed as to what to do next.

AND…I’d really like to know the proper way of doing what I tried and failed to do (simply add two extensions as “registered”).

Maybe I have some misunderstanding of this feature, but I thought you had to run in Admin mode to configure this. Perhaps not.

It still doesn’t seem to explain why, for my non-Admin mode running of Notepad++, that I went from 0 registered extensions, to 10…