Introduction

User subroutine for the definition of a user module. The following example illustrates the creation of user arrays called rwork and iwork.

Arrays declaration

The first step is to declare these two arrays at the very beginning of the module. The first one iwork is an allocatable array of one dimension whereas rwork is a pointer to a bidimensionnal array.

  ! Example: allocatable user arrays
  integer,          dimension(:), allocatable :: iwork
  double precision, dimension(:,:), pointer :: rwork => null()

Arrays allocation

The init_user_module subroutine allocates rwork and iwork if they are not already allocated or associated (for rwork).

  ! Allocate arrays
  subroutine init_user_module(ncel, ncelet)
    ! Arguments
    integer, intent(in) :: ncel, ncelet
    ! Local variables
    integer :: err = 0
    if (.not.allocated(iwork)) then
      allocate(iwork(ncelet), stat=err)
    endif
    if (err .eq. 0 .and. .not.associated(rwork)) then
      allocate(rwork(3, ncelet), stat=err)
    endif
    if (err /= 0) then
      write (*, *) "Error allocating array."
      call csexit(err)
    endif
    return
  end subroutine init_user_module

Access to arrays in C

It is possible to access the rwork array in the C part of the code. This can be done by using the get_user_module_rwork subroutine.

  ! Pass pointer to rwork array to C
  function get_user_module_rwork() result(r) &
    bind(c, name='get_user_module_rwork')
    use, intrinsic :: iso_c_binding
    implicit none
    type(c_ptr) :: r
    if (associated(rwork)) then
      r = c_loc(rwork(1,1))
    else
      r = c_null_ptr
    endif
  end function get_user_module_rwork

Arrays freeing

Eventually, the finalize_user_module subroutine is used to free iwork and rwork.

  ! Free related arrays
  subroutine finalize_user_module
    if (allocated(iwork)) then
      deallocate(iwork)
    endif
    if (associated(rwork)) then
      deallocate(rwork)
    endif
  end subroutine finalize_user_module