Rules for inlude files: - include files from the current subdir via #include "abc.h" - include header from other subdirs vai #include <def.h> ( do NOT use a specific path - this may change!) - include privtae header files via path: #include "../other_dir/ppp.h" - should be avoided! Classes of files - public header: - should be installed at a central place ($includedir) - should itself only include other public headers - private header: - will not be installed at other places - will (usually) only be included from that subdir