CODEWITHSUNDEEP
fortran
David Wilson
David Wilson

Reputation: 23

Array of unknown rank as subroutine argument

I am designing a module which works with the hdf5 Fortran library. This module contains subroutines to read and write arrays of different types and shapes to/from a file.

e.g. I wish to be able to call writeToHDF5(filepath, array) regardless of what the shape and type of array is. I realise that interfaces have to be used to achieve this with different types. I am however wondering if it is possible to have an assumed shape of the array.

e.g.

if an array was defined such as 

integer(kind=4), dimension(*),intent(in) :: array

and a two dimensional array was passed this would work. Is there any way to do this without creating separate subroutines for each shape of the array?

Upvotes: 2

Views: 1577

Answers (2)

TheWhitestOfFangs
TheWhitestOfFangs

Reputation: 465

I know that this comes out late, but for any future readers - the answer is actually yes. This is a simple example of a procedure to read a single data-set of integers with any given shape. The inputs needed were read from the HDF5 using a single routine which does not require any special specification and are the same for integer, real, string and so on. I have tested it on a "0-D" array (so size of (/1/) ), 1-D, 2-D, 3-D and 4-D arrays. In all cases, the data was retrieved properly. (Note: I removed some checks regarding the Errorflag, as they are not critical for the example)

  subroutine ReadSingleDataset_int(FileName,DataName,DataType,Data_dims,Errorflag,InputArray)
  implicit none
  character(len=*), intent(in) :: FileName,DataName
  integer(HID_T), intent(in)   :: DataType
  integer(hsize_t), dimension(:), intent(in) :: Data_dims
  logical, intent(out) :: ErrorFlag
  integer, dimension(*), intent(inout) :: InputArray

  integer :: hdferr
  integer(HID_T) :: file_id,dset_id

  ErrorFlag=.FALSE.

  IF (.NOT.HDF5_initialized) THEN
     CALL h5open_f(hdferr)
     HDF5_initialized=.TRUE.
  ENDIF

  call h5fopen_f(trim(FileName),H5F_ACC_RDONLY_F, file_id, hdferr)
  call h5dopen_f(file_id,trim(DataName),dset_id,hdferr)

  call h5dread_f(dset_id,DataType,InputArray,Data_dims,hdferr)

  call h5dclose_f(dset_id,hdferr)
  call h5fclose_f(file_id,hdferr)

  end subroutine ReadSingleDataset_int

My main interest in this now is - would it be possible to replace the type/class specific (integer/real/etc') with a generic one on the lines of:

class(*), dimension(*), intent(inout) :: InputArray

As I have several routines like that (for int, real, string) which only vary in that specification of the input type/class. If that limitation could be alleviated as well, that will be even more elegant. (Just to point out the issue - the h5dread_f does not accept the buffer argument, InputArray in my case, to be unlimited polymorphic)

Upvotes: 0

Steve Lionel
Steve Lionel

Reputation: 7267

As Vladimir F says, Fortran 2015 adds "assumed-rank" - this is useful Fortran-Fortran (it was requested by MPI for the Fortran bindings), but when you receive such an array, you can't do much with it directly without additional complications. Several compilers support this already, but few (if any?) support the newly added SELECT RANK construct that make this a bit more useful.

You can, however, use C_LOC and C_F_POINTER to "cast" the assumed-rank dummy to a pointer to an array of whatever rank you like, so that's a possibility.

The standard (even back to Fortran 90) does give you an out here. If you write:call writeToHDF5(filepath, array(1,1)) (assuming array is rank 2 here), the explicit interface of the called procedure can specify any rank for the dummy argument through the magic of "sequence association". There are some restrictions, though - in particular the array is not allowed to be assumed-shape or POINTER.

Upvotes: 6

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