[svn-r242] Example showing how to read from chunked dataset has been added.

examples/h5_chunk_read.c

@@ -0,0 +1,139 @@
+/*  
+ *   This example shows how to read data from a chunked dataset.
+ *   We will read from the file created by h5_extend_write.c 
+ */
+ 
+#include "hdf5.h"
+
+#define FILE        "SDSextendable.h5"
+#define DATASETNAME "ExtendableArray" 
+#define RANK         2
+#define NX     10
+#define NY     5 
+
+main ()
+{
+   hid_t       file;                        /* handles */
+   hid_t       datatype, dataset;  
+   hid_t       filespace;                   
+   hid_t       memspace;                  
+   hid_t       cparms;                   
+   H5T_class_t class;                       /* data type class */
+   size_t      elem_size;                   /* size of the data element
+                                               stored in file */ 
+   size_t      dims[2];                     /* dataset and chunk dimensions */ 
+   size_t      chunk_dims[2];
+
+   size_t      size[2];
+   size_t      count[2];
+   int         offset[2];
+
+   herr_t      status, status_n;                             
+
+   int         data_out[NX][NY];  /* buffer for dataset to be read */
+   int         chunk_out[2][5];   /* buffer for chunk to be read */
+   int         i, j, rank, rank_chunk;
+
+ 
+/*
+ * Open the file and the dataset.
+ */
+file = H5Fopen(FILE, H5ACC_DEFAULT, H5C_DEFAULT);
+dataset = H5Dopen(file, DATASETNAME);
+ 
+/*
+ * Get dataset rank and dimension.
+ */
+ 
+filespace = H5Dget_space(dataset);    /* Get filespace handle first. */
+rank      = H5Pget_ndims(filespace);
+status_n  = H5Pget_dims(filespace, dims);
+printf("dataset rank %d, dimensions %d x %d \n", rank, dims[0], dims[1]);
+
+/*
+ * Get creation properties.
+ */
+cparms = H5Dget_create_parms(dataset); /* Get properties handle first. */
+
+/*
+ * Get chunking information: rank and dimensions
+ */
+rank_chunk = H5Cget_chunk(cparms, 2, chunk_dims);
+printf("chunk rank %d, dimensions %d x %d \n", rank_chunk,
+        chunk_dims[0], chunk_dims[1]);
+ 
+ 
+/*
+ * Define the memory space to read dataset.
+ */
+memspace = H5Pcreate_simple(RANK,dims,NULL);
+ 
+/*
+ * Read dataset back and display.
+ */
+status = H5Dread(dataset, H5T_NATIVE_INT, memspace, filespace,
+                 H5C_DEFAULT, data_out);
+    printf("\n");
+    printf("Dataset: \n");
+for (j = 0; j < dims[0]; j++) {
+    for (i = 0; i < dims[1]; i++) printf("%d ", data_out[j][i]);
+    printf("\n");
+}     
+
+/*
+            dataset rank 2, dimensions 10 x 5 
+            chunk rank 2, dimensions 2 x 5 
+
+            Dataset:
+            1 1 1 3 3 
+            1 1 1 3 3 
+            1 1 1 0 0 
+            2 0 0 0 0 
+            2 0 0 0 0 
+            2 0 0 0 0 
+            2 0 0 0 0 
+            2 0 0 0 0 
+            2 0 0 0 0 
+            2 0 0 0 0 
+*/
+
+/*
+ * Define the memory space to read a chunk.
+ */
+memspace = H5Pcreate_simple(rank_chunk,chunk_dims,NULL);
+
+/*
+ * Define chunk in the file (hyperslab) to read.
+ */
+offset[0] = 2;
+offset[1] = 0;
+count[0]  = chunk_dims[0];
+count[1]  = chunk_dims[1];
+status = H5Pset_hyperslab(filespace, offset, count, NULL);
+
+/*
+ * Read chunk back and display.
+ */
+status = H5Dread(dataset, H5T_NATIVE_INT, memspace, filespace,
+                 H5C_DEFAULT, chunk_out);
+    printf("\n");
+    printf("Chunk: \n");
+for (j = 0; j < chunk_dims[0]; j++) {
+    for (i = 0; i < chunk_dims[1]; i++) printf("%d ", chunk_out[j][i]);
+    printf("\n");
+}     
+/*
+         Chunk: 
+         1 1 1 0 0 
+         2 0 0 0 0 
+*/
+
+/*
+ * Close/release resources.
+ */
+H5Dclose(dataset);
+H5Pclose(filespace);
+H5Pclose(memspace);
+H5Fclose(file);
+
+}