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

On 2025-02-05, Alan Mackenzie <acm@muc.de> wrote:

Hello, comp.lang.c.
>
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?

All that stuff depends on the GCC installation, and therefore cannot
be specified in concrete terms in a general document.

Unfortunately

  gcc -print-search-dirs

does not have info about the include file search directories. I'm guessing that
could have to do with the split between the compiler and preprocessor.

Anyway, we can coax the information out of the preprocessing stuff,
by adding the -v option to gcc -E.

Try this:

$ echo | gcc -xc -E -v - 2>&1 | awk '/include.*search starts here/,/End of search list/'
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/i686-linux-gnu/7/include
 /usr/local/include
 /usr/lib/gcc/i686-linux-gnu/7/include-fixed
 /usr/include/i386-linux-gnu
 /usr/include
End of search list.

The above happens to come from a 32 bit Ubuntu 18 VM, that I maintain for
compiling for 32 bit Intel. (You cannot install that from scratch; 32 bit
support started to be deprecated after Ubuntu 16; I created that VM by
upgrading from 16.)


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