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HDF5 requires you to use chunking in order to define extendible datasets. Chunking makes it possible to extend datasets efficiently, without having to reorganize storage excessively.
The following operations are required in order to write an extendible dataset:
/**************************************************************
*
* This example shows how to work with extendible datasets.
* In the current version of the library a dataset MUST be
* chunked in order to be extendible.
*
* This example is derived from the h5_extend_write.c and
* h5_read_chunk.c examples that are in the "Introduction
* to HDF5".
*
*************************************************************/
#include "hdf5.h"
#define FILE "ext.h5"
#define DATASETNAME "ExtendibleArray"
#define RANK 2
int
main (void)
{
hid_t file; /* handles */
hid_t dataspace, dataset;
hid_t filespace;
hid_t cparms;
hid_t memspace;
hsize_t dims[2] = { 3, 3}; /* dataset dimensions
at creation time */
hsize_t dims1[2] = { 3, 3}; /* data1 dimensions */
hsize_t dims2[2] = { 7, 1}; /* data2 dimensions */
hsize_t maxdims[2] = {H5S_UNLIMITED, H5S_UNLIMITED};
hsize_t size[2];
hssize_t offset[2];
hsize_t i,j;
herr_t status, status_n;
int data1[3][3] = { {1, 1, 1}, /* data to write */
{1, 1, 1},
{1, 1, 1} };
int data2[7] = { 2, 2, 2, 2, 2, 2, 2};
/* Variables used in reading data back */
hsize_t chunk_dims[2] ={2, 5};
hsize_t chunk_dimsr[2];
hsize_t dimsr[2];
int data_out[10][3];
int rank, rank_chunk;
/* Create the data space with unlimited dimensions. */
dataspace = H5Screate_simple (RANK, dims, maxdims);
/* Create a new file. If file exists its contents will be overwritten. */
file = H5Fcreate (FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
/* Modify dataset creation properties, i.e. enable chunking */
cparms = H5Pcreate (H5P_DATASET_CREATE);
status = H5Pset_chunk ( cparms, RANK, chunk_dims);
/* Create a new dataset within the file using cparms
creation properties. */
dataset = H5Dcreate (file, DATASETNAME, H5T_NATIVE_INT, dataspace,
cparms);
/* Extend the dataset. This call assures that dataset is 3 x 3.*/
size[0] = 3;
size[1] = 3;
status = H5Dextend (dataset, size);
/* Select a hyperslab */
filespace = H5Dget_space (dataset);
offset[0] = 0;
offset[1] = 0;
status = H5Sselect_hyperslab (filespace, H5S_SELECT_SET, offset, NULL,
dims1, NULL);
/* Write the data to the hyperslab */
status = H5Dwrite (dataset, H5T_NATIVE_INT, dataspace, filespace,
H5P_DEFAULT, data1);
/* Extend the dataset. Dataset becomes 10 x 3 */
dims[0] = dims1[0] + dims2[0];
size[0] = dims[0];
size[1] = dims[1];
status = H5Dextend (dataset, size);
/* Select a hyperslab */
filespace = H5Dget_space (dataset);
offset[0] = 3;
offset[1] = 0;
status = H5Sselect_hyperslab (filespace, H5S_SELECT_SET, offset, NULL,
dims2, NULL);
/* Define memory space */
dataspace = H5Screate_simple (RANK, dims2, NULL);
/* Write the data to the hyperslab */
status = H5Dwrite (dataset, H5T_NATIVE_INT, dataspace, filespace,
H5P_DEFAULT, data2);
/* Close resources */
status = H5Dclose (dataset);
status = H5Sclose (dataspace);
status = H5Sclose (filespace);
status = H5Fclose (file);
/****************************************************************
Read the data back
***************************************************************/
file = H5Fopen (FILE, H5F_ACC_RDONLY, H5P_DEFAULT);
dataset = H5Dopen (file, DATASETNAME);
filespace = H5Dget_space (dataset);
rank = H5Sget_simple_extent_ndims (filespace);
status_n = H5Sget_simple_extent_dims (filespace, dimsr, NULL);
cparms = H5Dget_create_plist (dataset);
if (H5D_CHUNKED == H5Pget_layout (cparms))
{
rank_chunk = H5Pget_chunk (cparms, 2, chunk_dimsr);
}
memspace = H5Screate_simple (rank,dimsr,NULL);
status = H5Dread (dataset, H5T_NATIVE_INT, memspace, filespace,
H5P_DEFAULT, data_out);
printf("\n");
printf("Dataset: \n");
for (j = 0; j < dimsr[0]; j++)
{
for (i = 0; i < dimsr[1]; i++)
printf("%d ", data_out[j][i]);
printf("\n");
}
status = H5Pclose (cparms);
status = H5Dclose (dataset);
status = H5Sclose (filespace);
status = H5Sclose (memspace);
status = H5Fclose (file);
}
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
hid_t H5Pcreate ( H5P_class_t type )
herr_t H5Pset_chunk ( hid_t plist, int ndims, const hsize_t * dim )
A non-negative value is returned if successful; otherwise a negative value is returned.
herr_t H5Dextend ( hid_t dataset_id, const hsize_t * size )
This function returns a non-negative value if successful; otherwise it returns a negative value.
int H5Pget_chunk ( hid_t plist, int max_ndims, hsize_t * dims )
herr_t H5Pclose ( hid_t plist )where plist is the identifier of the property list to terminate access to.