gcc / g++ find where a header file is included from

To list absolute paths of include files, use

-M

Instead of outputting the result of preprocessing, output a rule suitable for make describing the dependencies of the main source file. The preprocessor outputs one make rule containing the object file name for that source file, a colon, and the names of all the included files, including those coming from -include or -imacros command line options.

gcc  -M test.c

If you dont want the system includes like

#include <stdio.h>

then use

-MM

Like -M but do not mention header files that are found in system header directories, nor header files that are included, directly or indirectly, from such a header.

gcc  -MM test.c