Directories for gcc

[Yong Mao]

Hi all,

I'm new to using gcc on Linux. Now I have got a question. I know that we can
use -I option to indicate the include directory so that the compiler can
find my own .h files. I know I don't have to specify the include directories
for some system .h files ( stdio.h  for instance, is put under /usr/include
and gcc will go to search that directory ) . My question is  how the
compiler decides the search directories for the system include files.  Is
this configurable somewhere or built into the binary of the gcc?

A similar case is the man command which will look up the /etc/man.config
file to decide the directories for the man pages search and therefore I can
control the search directories by writing the content of the /etc/man.config
file.

Thanks.