gfortran: default include search path? - gfortran

Question

How do you find the default search path for include files for gfortran?
For gcc, a past Q&A showed this website:
https://gcc.gnu.org/onlinedocs/gcc-4.1.1/cpp/Search-Path.html#Search-Path
But,
I'm not sure if it applies to gfortran.
I don't think it always applies.
For example, on an Linux server, (for lack of any other method) I did this
strace gfortran try.f90 > tmp.txt 2>&1
and found this particular gfortran searches directories like
/opt/intel/compilers_and_libraries_2016.2.181/linux/ipp/lib/intel64/x86_64-redhat-linux/4.4.7/finclude
and it does not search /usr/include . Apparently, this particular gfortran came with the Intel Fortran compiler and was customized.
So, my question is, is strace the only way to know what the default search paths are? (I need to know this, because I'm remotely helping a friend. I don't have direct access to his machine.)
Update: I should have mentioned the -print-search-dirs option. It doesn't include the "include" search path:
gfortran -print-search-dirs | grep --color include
The output of -print-search-dirs doesn't include the directories which strace indicates in the above experiment of mine.
Update2: I've just found that the gfortran on ubuntu searches only /usr/lib/gcc/x86_64-linux-gnu/7/finclude. I'm surprised that it doesn't even search /usr/include. So far, it seems we have to use -I/usr/include whereas we don't need -L/usr/lib . . . Does somebody know the reason for this asymmetry?
Update3: The answer below shows how to list include search paths:
echo | gfortran -E -Wp,-v -
Unfortunately, this one lists the paths only of the preprocessor (for #include), not for the INCLUDE statement of the Fortran language.
You can verify this by looking into one of the directories which the preprocessor does search. For example, I found cpuid.h in one of them. So, I compared
include 'cpuid.h'
with
#include "cpuid.h"
in a Fortran source program. Of course, either causes error, but the error messages make it clear that in the former case, the file isn't found and in the latter, the include file is found and inserted into the source code and that caused compile error.
Incidentally, this exercise showed that on my Linux server, gfortran searches /usr/lib/gcc/ . . . /finclude among other directories whereas its preprocessor searches /usr/lib/gcc/ . . . /include , which kind of makes sense.

Answer 1

For me
gfortran -print-search-dirs
does the trick.
My version
gfortran --version
GNU Fortran (GCC) 5.3.0
Copyright (C) 2015 Free Software Foundation, Inc.
GNU Fortran comes with NO WARRANTY, to the extent permitted by law.
You may redistribute copies of GNU Fortran
under the terms of the GNU General Public License.
For more information about these matters, see the file named COPYING
I don't use it often and not a FORTRAN expert, so hope this helps.
Update
I looked back on some old notes and found this incantation:
echo | gfortran -E -Wp,-v -
Perhaps this is more useful?