How to use fortran module subroutine in c

Question

I'm trying to use a fortran module subroutine in c and cannot get through, here is a simplified version of my problem:

I have one fortran module that contains a subroutine, and the second subroutine uses the module.

!md.f90
module myadd
implicit none
contains

subroutine add1(a) bind(c)
implicit none
integer a
a=a+1

end subroutine add1
end module myadd


!sb.f90
subroutine sq(a) bind(c)
use myadd
implicit none
integer a
call add1(a)
a=a*a
end subroutine sq

Now I want to call the sb function in c:

//main.cpp
extern "C"{ void sb(int * a); }
int main(){
  int a=2;
  sb(&a);
}

how should I link them together?

I tried something like

ifort -c md.f90 sb.f90
icc sb.o main.cpp

but it gives error

sb.o: In function sq': sb.f90:(.text+0x6): undefined reference toadd1' /tmp/icc40D9n7.o: In function main': main.cpp:(.text+0x2e): undefined reference tosb'

Does anyone know how to solve the problem?

Here's a related question: stackoverflow.com/questions/15557439/… — Jason
– Jason, Commented Jan 17, 2015 at 19:44

M. S. B. · Accepted Answer · 2013-10-13 04:09:33Z

3

int main(void){
  int a=2;
  sb(&a);
  return 0;
}

and

module myadd
use iso_c_binding
implicit none
contains

subroutine add1(a) bind(c)
implicit none
integer (c_int),intent (inout) :: a
a=a+1

end subroutine add1
end module myadd


!sb.f90
subroutine sq(a) bind(c, name="sb")
use iso_c_binding
use myadd
implicit none
integer (c_int), intent(inout) :: a
call add1(a)
a=a*a
end subroutine sq

with

gcc -c main.c
gfortran-debug fort_subs.f90 main.o

It is easier to link with the Fortran compiler because it brings in the Fortran libraries.

answered Oct 13, 2013 at 4:09

M. S. B.

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4 Comments

xslittlegrass Over a year ago

It works. Thanks a lot! Do you know how to do the same using intel compilers? I always get error with intel : main.o: In function main': main.c:(.text+0x0): multiple definition of main' for_main.o:/export/users/nbtester/efi2linux_nightly/branch-13_0/20120801_000000/libdev/frtl/src/libfor/for_main.c:(.text+0x0): first defined here /home/compilers/Intel/composer_xe_2013.0.079/compiler/lib/intel64/for_main.o: In function

main': /export/users/nbtester/efi2linux_nightly/branch-13_0/20120801_000000/libdev/frtl/src/libfor/for_main.c:(.text+0x38): undefined reference to

MAIN__'

Hristo Iliev Over a year ago

@xslittlegrass, if you use ifort to link Fortran code with a C/C++ main() function, you should give it the -nofor-main option, otherwise the compiler links the for_main.o object file, which contains a main function, which in turn calls the main Fortran program (usually named MAIN under the hood).

xslittlegrass Over a year ago

@HristoIliev It works! Thanks. Do you what is the compiler flag for icc to ask icc to bring in the fortran library?

Hristo Iliev Over a year ago

@xslittlegrass, I'm not aware of such option. It's probably best to use ifort to link mixed-language applications.

IanH · Accepted Answer · 2013-10-13 06:25:08Z

1

The reason for your link error is twofold:

you omitted the object file for the source file that holds the module from the final command line (md.o).
you've called sq in the fortran sb in the C++ code.

Fix those and you'll be right to go.

answered Oct 13, 2013 at 6:25

IanH

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