Signature:
  SUBROUTINE h5pget_virtual_dsetname_f(dcpl_id, index, name, hdferr, name_len)
    INTEGER(HID_T)  , INTENT(IN)  :: dcpl_id
    INTEGER(SIZE_T) , INTENT(IN)  :: index
    CHARACTER(LEN=*), INTENT(OUT) :: name
    INTEGER, INTENT(OUT)          :: hdferr
    INTEGER(SIZE_T), OPTIONAL     :: name_len
Optional parameters:
  name_len - The size of name needed to hold the source dataset name. (OUT)
Inputs:
  dcpl_id - The identifier of the virtual dataset creation property list.
  index   - Mapping index.
            The value of index is 0 (zero) or greater and less than count 
            (0 ≤ index < count), where count is the number of mappings 
            returned by h5pget_virtual_count.
Outputs:
  name   - A buffer containing the name of the source dataset.
  hdferr - Returns 0 if successful and -1 if fails.