This may seem like a silly question, but when you start autocad for the first time, it creates a profile with the default support file search paths. Where does AutoCAD get this from?
I want to use this for a tool I am creating.
Command: setvar acadprefix
will give you the support file search path (it was written to registry when you install AutoCAD)
clearify what do you mean by tool?
I believe the initial paths are partially hard-coded, using some of the installation information as the starting point for the drive and first few folders. You might be able to pull some of this information out of the registry, but it would be just as easy to hard-code it yourself in the registry or a data file rather than re-calculate it every time.
If you are going to fly by the seat of your pants, expect friction burns.
Adopt. Adapt. Overcome. Or be overcome.
here it is:-
HKCU\Software\Autodesk\AutoCAD\R1XX.X\ACAD-XXXX:XXX\Profiles\Your Default Profile\General\ACAD
where XXXX it is version dependet
in key "Profiles" you should read the (Default) key and have Your Default Profile
and key ACAD contains what you are after.