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Compound datatypes must be built out of other datatypes. First, one creates an empty compound datatype and specifies its total size. Then members are added to the compound datatype in any order.
h5_compound.c
Compound.java
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
#include "hdf5.h"
#define FILE "SDScompound.h5"
#define DATASETNAME "ArrayOfStructures"
#define LENGTH 10
#define RANK 1
int
main(void)
{
/* First structure and dataset*/
typedef struct s1_t {
int a;
float b;
double c;
} s1_t;
s1_t s1[LENGTH];
hid_t s1_tid; /* File datatype identifier */
/* Second structure (subset of s1_t) and dataset*/
typedef struct s2_t {
double c;
int a;
} s2_t;
s2_t s2[LENGTH];
hid_t s2_tid; /* Memory datatype handle */
/* Third "structure" ( will be used to read float field of s1) */
hid_t s3_tid; /* Memory datatype handle */
float s3[LENGTH];
int i;
hid_t file, dataset, space; /* Handles */
herr_t status;
hsize_t dim[] = {LENGTH}; /* Dataspace dimensions */
/*
* Initialize the data
*/
for (i = 0; i < LENGTH; i++) {
s1[i].a = i;
s1[i].b = i*i;
s1[i].c = 1./(i+1);
}
/*
* Create the data space.
*/
space = H5Screate_simple(RANK, dim, NULL);
/*
* Create the file.
*/
file = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
/*
* Create the memory datatype.
*/
s1_tid = H5Tcreate (H5T_COMPOUND, sizeof(s1_t));
H5Tinsert(s1_tid, "a_name", HOFFSET(s1_t, a), H5T_NATIVE_INT);
H5Tinsert(s1_tid, "c_name", HOFFSET(s1_t, c), H5T_NATIVE_DOUBLE);
H5Tinsert(s1_tid, "b_name", HOFFSET(s1_t, b), H5T_NATIVE_FLOAT);
/*
* Create the dataset.
*/
dataset = H5Dcreate(file, DATASETNAME, s1_tid, space, H5P_DEFAULT);
/*
* Wtite data to the dataset;
*/
status = H5Dwrite(dataset, s1_tid, H5S_ALL, H5S_ALL, H5P_DEFAULT, s1);
/*
* Release resources
*/
H5Tclose(s1_tid);
H5Sclose(space);
H5Dclose(dataset);
H5Fclose(file);
/*
* Open the file and the dataset.
*/
file = H5Fopen(FILE, H5F_ACC_RDONLY, H5P_DEFAULT);
dataset = H5Dopen(file, DATASETNAME);
/*
* Create a datatype for s2
*/
s2_tid = H5Tcreate(H5T_COMPOUND, sizeof(s2_t));
H5Tinsert(s2_tid, "c_name", HOFFSET(s2_t, c), H5T_NATIVE_DOUBLE);
H5Tinsert(s2_tid, "a_name", HOFFSET(s2_t, a), H5T_NATIVE_INT);
/*
* Read two fields c and a from s1 dataset. Fields in the file
* are found by their names "c_name" and "a_name".
*/
status = H5Dread(dataset, s2_tid, H5S_ALL, H5S_ALL, H5P_DEFAULT, s2);
/*
* Display the fields
*/
printf("\n");
printf("Field c : \n");
for( i = 0; i < LENGTH; i++) printf("%.4f ", s2[i].c);
printf("\n");
printf("\n");
printf("Field a : \n");
for( i = 0; i < LENGTH; i++) printf("%d ", s2[i].a);
printf("\n");
/*
* Create a datatype for s3.
*/
s3_tid = H5Tcreate(H5T_COMPOUND, sizeof(float));
status = H5Tinsert(s3_tid, "b_name", 0, H5T_NATIVE_FLOAT);
/*
* Read field b from s1 dataset. Field in the file is found by its name.
*/
status = H5Dread(dataset, s3_tid, H5S_ALL, H5S_ALL, H5P_DEFAULT, s3);
/*
* Display the field
*/
printf("\n");
printf("Field b : \n");
for( i = 0; i < LENGTH; i++) printf("%.4f ", s3[i]);
printf("\n");
/*
* Release resources
*/
H5Tclose(s2_tid);
H5Tclose(s3_tid);
H5Dclose(dataset);
H5Fclose(file);
return 0;
}
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
The program outputs the following:
Field c : 1.0000 0.5000 0.3333 0.2500 0.2000 0.1667 0.1429 0.1250 0.1111 0.1000 Field a : 0 1 2 3 4 5 6 7 8 9 Field b : 0.0000 1.0000 4.0000 9.0000 16.0000 25.0000 36.0000 49.0000 64.0000 81.0000 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
H5Tcreate creates a new datatype of the specified class with
the specified number of bytes.
hid_t H5Tcreate ( H5T_class_t class, size_t size )
H5T_COMPOUND datatype class is supported with this
function.
H5Tinsert adds a member to the compound datatype specified by
type_id.
herr_t H5Tinsert ( hid_t type_id, const char * name, off_t offset,
hid_t field_id )
HOFFSET macro to compute the offset of a member within
a struct:
HOFFSET ( s, m )This macro computes the offset of member m within a struct variable s.
H5Tclose releases a datatype.
herr_t H5Tclose ( hid_t type_id )The type_id parameter is the identifier of the datatype to release.
HDF5 "SDScompound.h5" {
GROUP "/" {
DATASET "ArrayOfStructures" {
DATATYPE {
H5T_STD_I32BE "a_name";
H5T_IEEE_F32BE "b_name";
H5T_IEEE_F64BE "c_name";
}
DATASPACE { SIMPLE ( 10 ) / ( 10 ) }
DATA {
{
[ 0 ],
[ 0 ],
[ 1 ]
},
{
[ 1 ],
[ 1 ],
[ 0.5 ]
},
{
[ 2 ],
[ 4 ],
[ 0.333333 ]
},
{
[ 3 ],
[ 9 ],
[ 0.25 ]
},
{
[ 4 ],
[ 16 ],
[ 0.2 ]
},
{
[ 5 ],
[ 25 ],
[ 0.166667 ]
},
{
[ 6 ],
[ 36 ],
[ 0.142857 ]
},
{
[ 7 ],
[ 49 ],
[ 0.125 ]
},
{
[ 8 ],
[ 64 ],
[ 0.111111 ]
},
{
[ 9 ],
[ 81 ],
[ 0.1 ]
}
}
}
}
}