There three types of include files:

• Standard library headers. These are header files that are supplied by the system. These files are included with <> brackets, without the deprecated .h or .hpp suffix. E.g. #include <string>
• External library headers. This concerns non-standard header files that are provided by parties external to the software system that is being developed. These headers are also included with <> brackets. E.g. #include <boost/config.hpp>
• User headers. These are header files that are part of the software system that is being developed are included by means of "" quotes. E.g. #include "myheader.h"