Directories for gcc

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.

 

RE: Directories for gcc

[Rupert Wood]

Yong Mao wrote:

> 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?

Both, really.

A default set of directories is compiled in: look at gcc/protoize.c in
the source. You can see these from a binary gcc by compiling or
preprocessing any source with the '-v' switch.

You can also always add more directories on the command line using '-I'
or '-isystem'. You can probably also edit them into the compiler specs
file (<prefix>/lib/gcc-lib/<host>/version/specs) but I don't know much
about specs files. If you need more directories for a configure/make
source tree then you set -I switches in the CC or CFLAGS environments,
e.g. (bash)

    export CC="gcc -I/space/home/rmw/local/include"
  or
    export CFLAGS="-O2 -g -I/space/home/rmw/local/include"

Hope that helps,
Rup.

Re: Directories for gcc

[Axel Kittenberger]

> A default set of directories is compiled in: look at gcc/protoize.c in
> the source. You can see these from a binary gcc by compiling or
> preprocessing any source with the '-v' switch.
>
> You can also always add more directories on the command line using '-I'
> or '-isystem'. You can probably also edit them into the compiler specs
> file (<prefix>/lib/gcc-lib/<host>/version/specs) but I don't know much
> about specs files. If you need more directories for a configure/make
> source tree then you set -I switches in the CC or CFLAGS environments,
> e.g. (bash)

Might be worth a mention additionally if you don't want it to look in 
/usr/include for headers specify the command parameter:
--nostdinc

- Axel

RE: Directories for gcc

[Yong Mao]

Hi,

Thanks for the information. So the conclusion is that the standard search
directories for GCC have been hard-coded into the binary and you can only
add your own directories to it by some option or environment variables
setting.

Have a good day.

-----Original Message-----
From: Rupert Wood [mailto:me@rupey.net]
Sent: Thursday, December 13, 2001 4:38 PM
To: 'Yong Mao'
Cc: gcc-help@gcc.gnu.org
Subject: RE: Directories for gcc


Yong Mao wrote:

> 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?

Both, really.

A default set of directories is compiled in: look at gcc/protoize.c in
the source. You can see these from a binary gcc by compiling or
preprocessing any source with the '-v' switch.

You can also always add more directories on the command line using '-I'
or '-isystem'. You can probably also edit them into the compiler specs
file (<prefix>/lib/gcc-lib/<host>/version/specs) but I don't know much
about specs files. If you need more directories for a configure/make
source tree then you set -I switches in the CC or CFLAGS environments,
e.g. (bash)

    export CC="gcc -I/space/home/rmw/local/include"
  or
    export CFLAGS="-O2 -g -I/space/home/rmw/local/include"

Hope that helps,
Rup.