Handling Intel Fortran Pointers

Intel Fortran (integer) pointers are not the same as Fortran 90 pointers, but are instead like C pointers. On IA-32 systems, Intel Fortran pointers are 4-byte INTEGER quantities. On Itanium®-based systems, Intel Fortran pointers are 8-byte INTEGER quantities.

When passing an Intel Fortran pointer to a routine written in another language:

• The argument should be declared in the non-Fortran routine as a pointer of the appropriate data type.
• The argument passed from the Fortran routine should be the Intel Fortran pointer name, not the pointer-based variable name.

  For example, on IA-32 systems:
  ! Fortran main program.

        INTERFACE

           SUBROUTINE Ptr_Sub (p)

           !DEC$ ATTRIBUTES C, ALIAS:'_Ptr_Sub' :: Ptr_Sub

              INTEGER p

           END SUBROUTINE Ptr_Sub

        END INTERFACE

        REAL A(10), VAR(10)

        POINTER (p, VAR) ! VAR is the pointer-based

                         ! variable, p is the int.

        p = LOC(A)

        CALL Ptr_Sub (p)

        WRITE(*,*) 'A(4) = ', A(4)

        END

    !

    //C subprogram

        void Ptr_Sub (float *p)

        {

           p[3] = 23.5;

        }

  On Itanium-based systems, the alias name for Ptr_Sub should not have a leading underscore (see below) and the declaration for p in the INTERFACE block should be INTEGER(8)p:
  !DEC$ ATTRIBUTES C, ALIAS:'Ptr_Sub' :: Ptr_Sub

  When the main Fortran program and C function are built and executed, the following output appears:
  A(4) = 23.50000

When receiving a pointer from a routine written in another language:

• The argument should be declared in the non-Fortran routine as a pointer of the appropriate data type and passed as usual.
• The argument received by the Fortran routine should be declared as an Intel Fortran pointer name, then the POINTER statement should associate it with a pointer-based variable of the appropriate data type (matching the data type of the passing routine). When inside the Fortran routine, use the pointer-based variable to set and access what the pointer points to.

For example, on IA-32 systems:

 ! Fortran subroutine.
      SUBROUTINE Iptr_Sub (p)
      !DEC$ ATTRIBUTES C, ALIAS:'_Iptr_Sub' :: Iptr_Sub
         integer VAR(10)
         POINTER (p, VAR)
         OPEN (8, FILE='STAT.DAT')
         READ (8, *) VAR(4) ! Read from file and store the
                            ! fourth element of VAR
      END SUBROUTINE Iptr_Sub
 !
 //C main program
 extern void Iptr_Sub(int *p);
 main ( void )
 {
   int a[10];
   Iptr_Sub (&a[0]);
   printf("a[3] = %i\n", a[3]);
 }

   !DEC$ ATTRIBUTES C, ALIAS:'Iptr_Sub' :: Iptr_Sub

When the main C program and Fortran subroutine are built and executed, the following output appears if the STAT.DAT file contains 4:

   a[3] = 4