When creating an application that will be targeted to many versions of Windows what is the best practice to determine where application specific data should be stored. Specifically:
I know on Windows Vista for instance there are environment variables, like %APPDATA%, that could be used, but what about Windows 7, Windows XP, Windows 98.
My main question is, does Microsoft have a best practices doc for this, outlining the file system locations for the different types of data (app vs. user) and the security implications that need to be kept in mind when reading/writing to these locations?
I'm also interested in how this pertains to not only .NET applications (where ApplicationSettingsBase can be utilized) but also in unmanaged C/C++ applications.
Thanks to Pax and Remus for both of the great answers. I've found this item as well (specific to XP):
There's a good description here of the various CSIDL values and the folders they refer to (including a description which should hopefully tell you what you need to know).
It also contains links to the functions you should use to retrieve these special folder paths.
Note that, as of Vista, the method has changed a little. It now uses KNOWNFOLDERID instead of CSIDL and the functions have changed as well. See here.
You can still use the older functions (at the moment) since I believe they're now just wrappers around the new ones. At some point in the future, that may change.