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HDF5 Tutorial:   Learning The Basics
Reading from and Writing to a Dataset

Contents:


Reading from and Writing to a Dataset

During a dataset I/O operation, the library transfers raw data between memory and the file. The data in memory can have a datatype different from that of the file and can also be of a different size (i.e., the data in memory is a subset of the dataset elements, or vice versa). Therefore, to perform read or write operations, the application program must specify:

The steps to read from or write to a dataset are as follows:

To read from or write to a dataset, the H5Dread /h5dread_f and H5Dwrite / h5dwrite_f routines are used.

C:
   status = H5Dread (set_id, mem_type_id, mem_space_id, file_space_id,
                     xfer_prp, buf );
   status = H5Dwrite (set_id, mem_type_id, mem_space_id, file_space_id,
                     xfer_prp, buf);

FORTRAN:
   CALL h5dread_f(dset_id, mem_type_id, buf, dims, error, &
                     mem_space_id=mspace_id, file_space_id=fspace_id, &
                     xfer_prp=xfer_plist_id)
        or
   CALL h5dread_f(dset_id, mem_type_id, buf, dims,  error)


   CALL h5dwrite_f(dset_id, mem_type_id, buf, dims, error, &
                     mem_space_id=mspace_id, file_space_id=fspace_id, &
                     xfer_prp=xfer_plist_id)
        or
   CALL h5dwrite_f(dset_id, mem_type_id, buf, dims, error)

High Level APIs

The High Level HDF5 Lite APIs include functions that simplify and condense the steps for creating and reading datasets. Please be sure to review them, in addition to this tutorial.

Programming Example

Description

The following example shows how to read and write an existing dataset. It opens the file created in the previous example, obtains the dataset identifier for the dataset /dset, writes the dataset to the file, then reads the dataset back. It then closes the dataset and file.

Note that H5S_ALL is passed in for the memory and file dataspace parameters in the read and write calls. This indicates that the entire dataspace of the dataset will be read or written to.

See HDF5 Introductory Examples for the examples used in the Learning the Basics tutorial. There are examples for several other languages, including Java.

For details on compiling an HDF5 application: [ click here ]

Remarks

File Contents

Figure 6.1a shows the contents of dset.h5 (created by the C program).
Figure 6.1b shows the contents of dsetf.h5 (created by the FORTRAN program).

Fig. 6.1a   dset.h5 in DDL

      HDF5 "dset.h5" {
      GROUP "/" {
         DATASET "dset" {
            DATATYPE { H5T_STD_I32BE }
            DATASPACE { SIMPLE ( 4, 6 ) / ( 4, 6 ) }
            DATA {
               1, 2, 3, 4, 5, 6,
               7, 8, 9, 10, 11, 12,
               13, 14, 15, 16, 17, 18,
               19, 20, 21, 22, 23, 24
            }
         }
      }
      }

Fig. 6.1b   dsetf.h5 in DDL

HDF5 "dsetf.h5" {
GROUP "/" {
   DATASET "dset" {
      DATATYPE { H5T_STD_I32BE }
      DATASPACE { SIMPLE ( 6, 4 ) / ( 6, 4 ) }
      DATA {
         1, 7, 13, 19,
         2, 8, 14, 20,
         3, 9, 15, 21,
         4, 10, 16, 22,
         5, 11, 17, 23,
         6, 12, 18, 24
      }
   }
}
}

- - Last modified: 21 December 2016