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From: Alan Mackenzie <acm@muc.de>
Newsgroups: comp.lang.c
Subject: Re: What are GCC's "Standard system directories" on GNU/Linux?
Date: Wed, 5 Feb 2025 13:58:33 -0000 (UTC)
Organization: muc.de e.V.
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References: <vnvik4$2qqi$1@news.muc.de> <slrnvq6ohl.983.dan@djph.net>
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Hello, Dan.

Dan Purgert <dan@djph.net> wrote:
> On 2025-02-05, Alan Mackenzie wrote:
>> In the GCC manual, section 3.16 "Options for Directory Search" partially
>> describes where, how, and in what order GCC finds #include files when
>> compiling.
>>
>> It's the "partially" bit which is getting on my nerves.  The manual
>> section contains a priority list for finding #include files, but the
>> fifth item just vaguely states:
>>
>>     5. Standard system directories are scanned.
>>
>> .  Which directories are these?  Where is this documented?

> It is, as I recall, defined at compile time of gcc. You can get your
> system-specific "standard system directories" by running the command:

>   echo | gcc -xc -E -v -

> It'll print out a bunch of stuff, starting off with the compile-time
> options that were used when compiling gcc itself.  The bit you're
> looking for being listed out under the heading:

>   #include <...> search starts here:


> HTH

Thank you indeed!  That was extremely helpful, and told me everything I
need to know.

I'm creating my own version of the linux kernel, and have several
application programs to build that must #include files from this version
rather than the standard ones.

The listing from the command you gave me tells me that <linux/kd.h> will
be read from /usr/include/linux/kd.h, and so on.  Now I know that, I can
amend the Makefiles.

> -- 
> |_|O|_| 
> |_|_|O| Github: https://github.com/dpurgert
> |O|O|O| PGP: DDAB 23FB 19FA 7D85 1CC1  E067 6D65 70E5 4CE7 2860

-- 
Alan Mackenzie (Nuremberg, Germany).