I know I'm not the first to need this. I am working on an in house created codebase and I would like to apply highlighting to it within Eclipse. In Notepad++ I can set language for the file I'm looking at. Is there any way to do this for Eclipse?
The code I'm working on would use the same syntax styling as C++.
Your best bet is to go to Preferences -> General -> Editors -> File associations. Add the file extension of the thing you are trying to open and add the C++ editor as the associated default editor.
If there is no file extension, then things are a little harder. Instead of double-clicking to open the file, right-click -> Open with... -> other -> C++ editor. This will remember your choice for that file only.