Re: What are GCC's "Standard system directories" on GNU/Linux?

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.

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Alan Mackenzie (Nuremberg, Germany).