hdf5/examples/h5_attribute.c

/* 
 *  This program illustrates the usage of the H5A Interface functions.
 *  It creates and writes a dataset, and then creates and writes array,
 *  scalar, and string attributes of the dataset. 
 *  Program reopens the file, attaches to the scalar attribute using
 *  attribute name and reads and displays its value. Then index of the
 *  third attribute is used to read and display attribute values.
 *  The H5Aiterate function is used to iterate through the dataset attributes,
 *  and display their names. The function is also reads and displays the values 
 *  of the array attribute. 
 */ 
 
#include <hdf5.h>

#define FILE "Attributes.h5"

#define RANK  1   /* Rank and size of the dataset  */ 
#define SIZE  7

#define ARANK  2   /* Rank and dimension sizes of the first dataset attribute */
#define ADIM1  2
#define ADIM2  3 
#define ANAME  "Float attribute"      /* Name of the array attribute */
#define ANAMES "Character attribute" /* Name of the string attribute */

herr_t attr_info(hid_t loc_id, const char *name, void *opdata); 
                                     /* Operator function */

int main (void)
{

   hid_t   file, dataset;       /* File and dataset identifiers */
   
   hid_t   fid;                 /* Dataspace identifier */
   hid_t   attr1, attr2, attr3; /* Attribute identifiers */
   hid_t   attr;
   hid_t   aid1, aid2, aid3;    /* Attribute dataspace identifiers */ 
   hid_t   atype;               /* Attribute type */

   hsize_t fdim[] = {SIZE};
   hsize_t adim[] = {ADIM1, ADIM2};  /* Dimensions of the first attribute  */
   
   float matrix[ADIM1][ADIM2]; /* Attribute data */ 

   herr_t  ret;                /* Return value */
   uint    i,j;                /* Counters */
   int     idx;                /* Attribute index */
   char    string_out[80];     /* Buffer to read string attribute back */
   int     point_out;          /* Buffer to read scalar attribute back */

/*
 * Data initialization.
 */
int vector[] = {1, 2, 3, 4, 5, 6, 7};  /* Dataset data */
int point = 1;                         /* Value of the scalar attribute */ 
char string[] = "ABCD";                /* Value of the string attribute */

   
for (i=0; i < ADIM1; i++) {            /* Values of the array attribute */
    for (j=0; j < ADIM2; j++)
        matrix[i][j] = -1.;
}

/*
 * Create a file.
 */
file = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

/* 
 * Create the dataspace for the dataset in the file.
 */
fid = H5Screate(H5S_SIMPLE);
ret = H5Sset_extent_simple(fid, RANK, fdim, NULL);

/*
 * Create the dataset in the file.
 */
dataset = H5Dcreate(file, "Dataset", H5T_NATIVE_INT, fid, H5P_DEFAULT);

/*
 * Write data to the dataset.
 */
ret = H5Dwrite(dataset, H5T_NATIVE_INT, H5S_ALL , H5S_ALL, H5P_DEFAULT, vector);

/*
 * Create dataspace for the first attribute. 
 */
aid1 = H5Screate(H5S_SIMPLE);
ret  = H5Sset_extent_simple(aid1, ARANK, adim, NULL);

/*
 * Create array attribute.
 */
attr1 = H5Acreate(dataset, ANAME, H5T_NATIVE_FLOAT, aid1, H5P_DEFAULT);

/*
 * Write array attribute.
 */
ret = H5Awrite(attr1, H5T_NATIVE_FLOAT, matrix);

/*
 * Create scalar attribute.
 */
aid2  = H5Screate(H5S_SCALAR);
attr2 = H5Acreate(dataset, "Integer attribute", H5T_NATIVE_INT, aid2,
                  H5P_DEFAULT);

/*
 * Write scalar attribute.
 */
ret = H5Awrite(attr2, H5T_NATIVE_INT, &point); 

/*
 * Create string attribute.
 */
aid3  = H5Screate(H5S_SCALAR);
atype = H5Tcopy(H5T_C_S1);
        H5Tset_size(atype, 4);
attr3 = H5Acreate(dataset, ANAMES, atype, aid3, H5P_DEFAULT);

/*
 * Write string attribute.
 */
ret = H5Awrite(attr3, atype, string); 

/*
 * Close attribute and file datapsaces.
 */
ret = H5Sclose(aid1); 
ret = H5Sclose(aid2); 
ret = H5Sclose(aid3); 
ret = H5Sclose(fid); 

/*
 * Close the attributes.
 */ 
ret = H5Aclose(attr1);
ret = H5Aclose(attr2);
ret = H5Aclose(attr3);
 
/*
 * Close the dataset.
 */
ret = H5Dclose(dataset);

/*
 * Close the file.
 */
ret = H5Fclose(file);

/*
 * Reopen the file.
 */
file = H5Fopen(FILE, H5F_ACC_RDONLY, H5P_DEFAULT);

/*
 * Open the dataset.
 */
dataset = H5Dopen(file,"Dataset");

/*
 * Attach to the scalar attribute using attribute name, then read and 
 * display its value.
 */
attr = H5Aopen_name(dataset,"Integer attribute");
ret  = H5Aread(attr, H5T_NATIVE_INT, &point_out);
printf("The value of the attribute \"Integer attribute\" is %d \n", point_out); 
ret =  H5Aclose(attr);

/*
 * Attach to the string attribute using its index, then read and display the value.
 */
attr = H5Aopen_idx(dataset, 2);
atype = H5Tcopy(H5T_C_S1);
        H5Tset_size(atype, 4);
ret   = H5Aread(attr, atype, string_out);
printf("The value of the attribute with the index 2 is %s \n", string_out);
ret   = H5Aclose(attr);
ret   = H5Tclose(atype);

/*
 * Get attribute info using iteration function. 
 */
idx = H5Aiterate(dataset, NULL, attr_info, NULL);

/*
 * Close the dataset and the file.
 */
H5Dclose(dataset);
H5Fclose(file);
return 0;  
}

/*
 * Operator function.
 */
herr_t attr_info(hid_t loc_id, const char *name, void *opdata)
{
    hid_t attr, atype, aspace;  /* Attribute, datatype and dataspace identifiers */
    int   rank;
    hsize_t sdim[64]; 
    herr_t ret;
    int i;
    size_t npoints;             /* Number of elements in the array attribute. */ 
    float *float_array;         /* Pointer to the array attribute. */
/*
 * Open the attribute using its name.
 */    
    attr = H5Aopen_name(loc_id, name);

/*
 * Display attribute name.
 */
    printf("\n");
    printf("Name : ");
    puts(name);

/* 
 * Get attribute datatype, dataspace, rank, and dimensions.
 */
    atype = H5Aget_type(attr);
    aspace = H5Aget_space(attr);
    rank = H5Sextent_ndims(aspace);
    ret = H5Sextent_dims(aspace, sdim, NULL);
/*
 *  Display rank and dimension sizes for the array attribute.
 */

    if(rank > 0) {
    printf("Rank : %d \n", rank); 
    printf("Dimension sizes : ");
    for (i=0; i< rank; i++) printf("%d ", (int)sdim[i]);
    printf("\n");
    }

/*
 * Read array attribute and display its type and values.
 */

    if (H5T_FLOAT == H5Tget_class(atype)) {
    printf("Type : FLOAT \n"); 
    npoints = H5Sextent_npoints(aspace);
    float_array = (float *)malloc(sizeof(float)*(int)npoints); 
    ret = H5Aread(attr, atype, float_array);
    printf("Values : ");
    for( i = 0; i < npoints; i++) printf("%f ", float_array[i]); 
    printf("\n");
    free(float_array);
    }


/*
 * Release all identifiers.
 */
    H5Tclose(atype);
    H5Sclose(aspace);
    H5Aclose(attr);
    return 0;
}