Passing an array from fortran to a C++ function - c++

Question

I have a main program in Fortran. I am using Intel Visual Fortran XE 2011 on Visual Studio 2010. I would like to use a function which is coded in C++. The function I'm using is getting several arrays (input - set from the main fortran program) and use them to form an output array (to be returned to the main fortran program).
I've taken the following steps:
1)I created a Fortran project with the Fortran main program and module and I set it as "startup project".
2)I created a C++ project of type "static library".
3)I added $(IFORT_COMPILERvv)\compiler\lib\ia32 as explained here http://software.intel.com/en-us/articles/configuring-visual-studio-for-mixed-language-applications
The C++ static library is build with no problem.
The errors I get is about the declaration of the real(8) variables in the fortran program.
I get the following two errors for all real(8) declarations, i.e. 6 errors in total:
error #5082: Syntax error, found '(' when expecting one of: :: %FILL , TYPE BYTE CHARACTER CLASS DOUBLE DOUBLECOMPLEX DOUBLEPRECISION ...
error #5082: Syntax error, found '::' when expecting one of: ( * , ; [ / = =>
Here is the code I used:
Main Fortran Program:
Program Fort_call_C
use iso_c_binding
implicit none
interface
subroutine vec_sum_c(a,b,c) bind (C, name = "vec_sum_c")
use iso_c_binding
implicit none
real(8) (c_double), intent (in), dimension (*) :: a,b
real(8) (c_double), intent (out), dimension (*) :: c
end subroutine get_filled_ar
end interface
integer:: i
integer (c_int)::m
real(8)(c_double),dimension(:):: a, b, c
open(unit=10, file="input_arrays.txt",status="unknown")
read(10,*) m
allocate(a(m),b(m),c(m))
do i=1,m
read(10,*)a(i),b(i)
end do
close(10)
call vec_sum_c(m,a,b,c)
do i=1,m
print*, c(i)
end do
pause
end program
And the C++ function is:
extern"C" void vec_sum_c(int *m, double *a, double *b, double *c){
int mm = *m;
for(int i=0;i<=m-1;i++){
c[i]=a[i]+b[i];
}
}
Could anybody please help me with this issue?
And would you please let me know if the idea of sending a whole array from a fortran program to a c++ routine is a safe or problematic (better-to-be-avoided) attempt?

Answer 1

Your Fortran syntax is out. You have the real kind twice. Try
REAL(C_DOUBLE), INTENT(IN), DIMENSION(*) :: a, b
etc.
C_DOUBLE is a named constant. It happens to have the value 8 with that processor.
Also:
you are missing the argument m in the Fortran interface body for the C function.
you change your mind about the name of the subroutine in the Fortran interface body between the opening and closing statement!
Your C++ for loop less than equal compares against m, that should probably be mm.
There are no inherent problem sending whole arrays in this manner.

Answer 2

I had only managed to pass the value of a varible from C
function to fortran function.
I have here pasted the two source files namely main.c and fortran.f
You can use these two files in microsoft visual studio 10. After
doing all the settings in visual studio as suggested in page http://software.intel.com/en-us/articles/configuring-visual-studio-for-mixed-language-applications, you need to make another change as;
go to the project property of C/C++ static library ;
go to C/C++
go to Code Generation
set the Runtime Library to Multi-threaded Debug (/MTd)
now you can build the program....
main.c:
#include <stdio.h>
#include <malloc.h>
void testc(double **pa, double **p)
{
double b;
double *a, *c;
int m;
c = (double*) malloc(sizeof(double));
*c = 10;
*p = c;
a = (double*) malloc(sizeof(double)*5);
a[0]=1.23;
a[1]=2.46;
a[2]=3.69;
a[3]=4.11;
a[4]=7.21;
*pa=a;
for (m=0;m<5;m++)
{
b=a[m];
b=b+1.0;
a[m]=b;
}
}
fortran.f:
program test
use iso_c_binding
implicit none
interface
subroutine testc(pa, m) bind(c)
use iso_c_binding
type(c_ptr):: m
type(c_ptr):: pa
end subroutine testc
end interface
type(c_ptr) :: pa
type(c_ptr) :: m
real(c_double),pointer::fpa(:)
real(c_double),pointer::fm(:)
call testc(pa,m)
call c_f_pointer(pa, fpa, [5])
call c_f_pointer(m, fm, [1])
print *, fm(1)
print*, fpa(1)
pause
end program test