Dear all,
I am sorry if I am posing a stupid question, but it seems I cannot
really see how I can solve this on my own.
The problem is understanding HDF5's possibility of creating datasets
with slabs. For instance, write a 5x2 matrix with only one row set to {
42, 42 }.
As far as I've learned reading the docs, I create the file, the
dataspace with properties (5x2 of integers, for instance), and finally
the dataspace itself. Then I can select the hyperslab and write to it.
What I'm getting is junk. I suspect I'm writing what I'm not supposed to
write, or reading where I've not intended to read, or both. Here's the dump:
HDF5 "test.h5" {
GROUP "/" {
DATASET "dset" {
DATATYPE H5T_STD_I32BE
DATASPACE SIMPLE { ( 5, 2 ) / ( 5, 2 ) }
DATA {
(0,0): 704643072, 704643072,
(1,0): 0, 0,
(2,0): 16777216, 0,
(3,0): 16777216, 0,
(4,0): 16777216, 0
}
}
}
}
I've played with my values, with count, offset and block, but I cannot
grasp how it works.
The code is below, it is commented with what I think each instruction
does, and what each variable means.
I really hope you can help me.
Thank you!
#include "hdf5.h"
int main()
{
hid_t file_id, dataspace_id, dataset_id;
herr_t status;
int rank = 2; /* rank 2 tensor */
hsize_t dims[2] = { 5, 2 }; /* 5 rows, 2 columns */
hsize_t offset[2], stride[2], count[2], block[2];
int newdata[3] = { 42, 42 };
/* create file */
file_id = H5Fcreate("test.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
/* create dataspace */
dataspace_id = H5Screate_simple(rank, dims, NULL);
/* create dataset: the ACTUAL data */
dataset_id = H5Dcreate(file_id, "/dset", H5T_STD_I32BE, dataspace_id,
H5P_DEFAULT);
/* slab properties */
offset[0] = 1; /* row offset, select second row */
offset[1] = 0; /* col offset, first column*/
stride[0] = 1; /* select every 1 element, don't skip any row*/
stride[1] = 1; /* and don't skip any elements on columns */
count[0] = 1; /* select only one block per dimension */
count[1] = 1; /* supposing 1 block means one entire row with this */
block[0] = 1; /* size of the row block */
block[1] = 3; /* column block size */
/* select a slab */
status = H5Sselect_hyperslab(dataspace_id, H5S_SELECT_SET,
offset, stride, count, block);
/* write! */
status = H5Dwrite(dataset_id, H5T_STD_I32BE, H5S_ALL, H5S_ALL,
H5P_DEFAULT,
newdata);
/* close dataset */
status = H5Dclose (dataset_id);
/* close dataspace */
status = H5Sclose(dataspace_id);
/* close file */
status = H5Fclose(file_id);
return 0;
}
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