Get system-wide config/data location

[voltron]

Is it possible to get system-wide location of the config/data directory for any user with Qt? Something like C:\Users\AllUsers\AppData in Windows and /usr/local/share in Linux etc.

I checked Qt4 docs, seems QDesktopServices is the right class to use, but it returns only user folder not system-wide location. In Qt5 there is a QStandardPaths class, which can return both user and system-wide locations. But QStandardPaths::standardLocations(QStandardPaths::AppDataLocation) returns list of paths and I can't extract required path from this list, as there is no warranty that order of items in it always will be the same. Also from what I understand, result returned by QStandardPaths::locate(QStandardPaths::AppDataLocation, fileName) depends on the user who runs program, e.f. for ordinal user it will return user directory like /home/user/.local/share/someprog, for sysadmin /usr/local/share/someprog.

Any ideas how to get system-wide config/data directory in crossplatform way?
Thanks!