[FEAT]

[omaxian]

Is there a way to link fortran to C++ to python with pybind11?

Here is a simple example of what I mean. Suppose I have the following fortran module

! fortmodule.f90
module fortmodule
use iso_c_binding
implicit none

integer(C_INT), bind(C), dimension(5) :: numbers

contains

subroutine fortransub() bind(C)

   print *, "Hello from Fortran!"
   numbers(1) = 1
   numbers(2) = 2
   numbers(3) = 3
   numbers(4) = 4
   numbers(5) = 5

end subroutine

end module

And I wanted to link it with pybind11 doing something like:

// TestFortran.cpp
#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
#include <stdio.h>

extern "C" void fortransub();
extern "C" int numbers[5];

int makeMe()
{
   int i;
   printf("Hello from C!\n");
   fortransub();
   for (i=0; i<5; i=i+1)
      printf("%d ", numbers[i]);
   printf("\n");

return 0;
}


PYBIND11_MODULE(TestFortran, m) {
    
    m.def("makeMe", &makeMe, "Test fortran/C/python");
}

Is something like this possible? I am not sure how to compile if it is.

If it were pure C++ (i.e., if MakeMe were replaced with main) the compile statement would simply be:

g++ -c TestFortran.cpp
gfortran TestFortran.o fortmodule.f90

Is there a way to adapt this to pybind11? Thank you.

[bstaletic]

It should work fine. You need to compile code with -fPIC. Then, when linking the shared objects, use -shared. For a simple, single-file, extension modules, I use this:

g++ -fPIC -shared foo.cpp -o foo.so -isystem /usr/include/python3.9

[omaxian]

Yes, the key is to compile the fortran into a library and then call it that way. Thank you.