Should I use #include in headers?

Question

Is it necessary to #include some file, if inside a header (*.h), types defined in this file are used?

For instance, if I use GLib and wish to use the

Answer 1

What I normally do is make a single include file that includes all necessary dependencies in the right order. So I might have:

#ifndef _PROJECT_H_
#define _PROJECT_H_
#include 
#include "my_project_types.h"
#include "my_project_implementation_prototypes.h"
#endif

All in project.h. Now project.h can be included anywhere with no order requirements but I still have the luxury of having my dependencies, types, and API function prototypes in different headers.