If mem_type_id is either a fixed-length or variable-length string, it is important to set the string length when defining the datatype. String datatypes are derived from H5T_C_S1 (or H5T_FORTRAN_S1 for Fortran codes), which defaults to 1 character in size. See H5Tset_size and “Creating variable-length string datatypes.”

file_space_id is used to specify only the selection within the file dataset's dataspace. Any dataspace specified in file_space_id is ignored by the library and the dataset's dataspace is always used. file_space_id can be the constant H5S_ALL. which indicates that the entire file dataspace, as defined by the current dimensions of the dataset, is to be selected.

mem_space_id is used to specify both the memory dataspace and the selection within that dataspace. mem_space_id can be the constant H5S_ALL, in which case the file dataspace is used for the memory dataspace and the selection defined with file_space_id is used for the selection within that dataspace.

The behavior of the library for the various combinations of valid dataspace IDs and H5S_ALL for the mem_space_id and the file_space_id parameters is described below:

mem_space_id	file_space_id	Behavior
valid dataspace identifier	valid dataspace identifier	mem_space_id specifies the memory dataspace and the selection within it. file_space_id specifies the selection within the file dataset's dataspace.
H5S_ALL	valid dataspace identifier	The file dataset's dataspace is used for the memory dataspace and the selection specified with file_space_id specifies the selection within it. The combination of the file dataset's dataspace and the selection from file_space_id is used for memory also.
valid dataspace identifier	H5S_ALL	mem_space_id specifies the memory dataspace and the selection within it. The selection within the file dataset's dataspace is set to the "all" selection.
H5S_ALL	H5S_ALL	The file dataset's dataspace is used for the memory dataspace and the selection within the memory dataspace is set to the "all" selection. The selection within the file dataset's dataspace is set to the "all" selection.

Setting an "all" selection indicates that the entire dataspace, as defined by the current dimensions of a dataspace, will be selected. The number of elements selected in the memory dataspace must match the number of elements selected in the file dataspace.

xfer_plist_id can be the constant H5P_DEFAULT. in which case the default data transfer properties are used.

Writing to an dataset will fail if the HDF5 file was not opened with write access permissions.

Datatype conversion takes place at the time of a read or write and is automatic. See the “Data Transfer: Datatype Conversion and Selection” section in the “HDF5 Datatypes” chapter of the HDF5 User’s Guide for a discussion of data conversion.

If the dataset's space allocation time is set to H5D_ALLOC_TIME_LATE or H5D_ALLOC_TIME_INCR and the space for the dataset has not yet been allocated, that space is allocated when the first raw data is written to the dataset. Unused space in the dataset will be written with fill values at the same time if the dataset's fill time is set to H5D_FILL_TIME_IFSET or H5D_FILL_TIME_ALLOC. (Also see H5Pset_fill_time and H5Pset_alloc_time.)

If a dataset's storage layout is 'compact', care must be taken when writing data to the dataset in parallel. A compact dataset's raw data is cached in memory and may be flushed to the file from any of the parallel processes, so parallel applications should always attempt to write identical data to the dataset from all processes.

SUBROUTINE h5dwrite_f(dset_id, mem_type_id, buf, dims, hdferr, & 
                      mem_space_id, file_space_id, xfer_prp)
  IMPLICIT NONE
  INTEGER(HID_T), INTENT(IN) :: dset_id      ! Dataset identifier
  INTEGER(HID_T), INTENT(IN) :: mem_type_id  ! Memory datatype identifier
  TYPE, INTENT(IN) :: buf                    ! Data buffer; may be a scalar 
                                             ! or an array
  DIMENSION(*), INTEGER(HSIZE_T), INTENT(IN)  :: dims 
                                             ! Array to hold corresponding 
                                             ! dimension sizes of data 
                                             ! buffer buf; dim(k) has value 
                                             ! of the k-th dimension of 
                                             ! buffer buf; values are 
                                             ! ignored if buf is a scalar
  INTEGER, INTENT(OUT) :: hdferr             ! Error code 
                                             ! 0 on success and -1 on failure

  INTEGER(HID_T), OPTIONAL, INTENT(IN) :: mem_space_id 
                                             ! Memory dataspace identfier 
                                             ! Default value is H5S_ALL_F
  INTEGER(HID_T), OPTIONAL, INTENT(IN) :: file_space_id 
                                             ! File dataspace identfier 
                                             ! Default value is H5S_ALL_F

  INTEGER(HID_T), OPTIONAL, INTENT(IN) :: xfer_prp 
                                             ! Transfer property list 
                                             ! identifier; default value 
                                             ! is H5P_DEFAULT_F 
END SUBROUTINE h5dwrite_f
	

SUBROUTINE h5dwrite_vl_f(dset_id, mem_type_id, buf, dims, len, hdferr, & 
                     mem_space_id, file_space_id, xfer_prp)
  IMPLICIT NONE
  INTEGER(HID_T), INTENT(IN) :: dset_id     ! Dataset identifier
  INTEGER(HID_T), INTENT(IN) :: mem_type_id ! Memory datatype identifier
  TYPE, INTENT(IN), & DIMENSION(dims(1),dims(2)) :: buf
                                            ! Data buffer; may be a scalar 
                                            ! or an array
                                            ! TYPE must be one of the following
                                            !     INTEGER
                                            !     REAL
                                            !     CHARACTER
  INTEGER(HSIZE_T), INTENT(IN), DIMENSION(2)  :: dims 
                                            ! Array to hold corresponding 
                                            ! dimension sizes of data 
                                            ! buffer buf 
                                            ! dim(k) has value of the k-th 
                                            ! dimension of buffer buf
                                            ! Values are ignored if buf is 
                                            ! a scalar
  INTEGER(SIZE_T), INTENT(IN), DIMENSION(*)  :: len 
                                            ! Array to store length of
                                            ! each element
  INTEGER, INTENT(OUT) :: hdferr            ! Error code 
                                            ! 0 on success and -1 on failure
  INTEGER(HID_T), OPTIONAL, INTENT(IN) :: mem_space_id 
                                            ! Memory dataspace identfier 
                                            ! Default value is H5S_ALL_F 
  INTEGER(HID_T), OPTIONAL, INTENT(IN) :: file_space_id 
                                            ! File dataspace identfier 
                                            ! Default value is H5S_ALL_F
  INTEGER(HID_T), OPTIONAL, INTENT(IN) :: xfer_prp 
                                            ! Transfer property list identifier
                                            ! Default value is H5P_DEFAULT_F
END SUBROUTINE h5dwrite_vl_f