Hi Aman,
it seems to me the problem is that you still use the same type for the
dataset creation and dataset writing, and for the filetype the offset of
member b should be zero, since the file structure only consists of that
element. So I would think it should be like this (I do this
theoretically as I'm not familiar with the C++ API and using the C API
myself):
struct MemType { int a; int b; };
struct FileType { int b; };
mtype.insertMember("b", HOFFSET(MemType, b), datatype);
ftype.insertMember("b", HOFFSET(FileType, b), datatype);
H5::DataSetdataset = solution.createDataSet( "Well", ftype, dataspace,
ds_creatplist );
dataset.write( MemTypeVar, mtype );
Note that HOFFSET(FileType,b) would be just zero. But in any case the
main point is that for creating a dataset you use the file type (which
specifies what you want in the file), for writing you use the memtype
(which specifies what you have in memory). Both need to be valid types,
of course.
Werner
On 25.07.2016 23:18, Aman Verma wrote:
Werner,
I tried your suggestion (and various permutations along the same line).
For the example that you mention below, when I do:
H5::CompTypemtype(sizeof(MemType));
mtype.insertMember("b", HOFFSET(MemType, b), datatype);
H5::DataSetdataset = solution.createDataSet( "Well", mtype, dataspace,
ds_creatplist );
dataset.write( MemTypeVar, mtype );
This is the only variation that runs without errors. But it gives me
the same output as before (large file size, sizeof(MemType)).
When I do what you suggested:
H5::CompTypemtype(sizeof(MemType));
H5::CompTypeftype(sizeof(FileType));// addition to the above code
mtype.insertMember("b", HOFFSET(MemType, b), datatype);
H5::DataSetdataset = solution.createDataSet( "Well", ftype, dataspace,
ds_creatplist );// changed from the above code
dataset.write( MemTypeVar, ftype );// changed from the above code
I get a runtime error ‘unable to create a dataset’ (obviously as I am
not inserting anything into ftype).
Now when I insert into ftype:
H5::CompTypemtype(sizeof(MemType));
H5::CompTypeftype(sizeof(FileType));
ftype.insertMember("b", HOFFSET(FileType, b), datatype);// changed
from the above code
H5::DataSetdataset = solution.createDataSet( "Well", ftype, dataspace,
ds_creatplist );
dataset.write( MemTypeVar, ftype );
I get a smaller size file (as expected, sizeof(FileType)). However the
data being written is controlled only by the offset (here, 0) and
hence it writes all the data from MemType with offset 0 (both a and b).
Hope this explains my problem. What statement(s) am I missing here to
(a) provide the stride in MemType or to (b) write out the ‘b’
component specifically? Could you give a small example of how to
achieve what you laid out in the last email?
Thanks,
Aman
*From:*Hdf-forum [mailto:[email protected]] *On
Behalf Of *Werner Benger
*Sent:* Friday, July 22, 2016 2:47 PM
*To:* [email protected]
*Subject:* Re: [Hdf-forum] [Ext] Re: Writing subset of compound datatype
Hi Aman,
the file type would need to be a compound type as well with a member
name equal to the member in the memory type. Then HDF5 can convert it.
An elementtype of float would not work, but something like
struct MemType { int a, b; };
struct FileType { int b; };
Then if you have an in-memory array of type MemType and dataset of
type FileType, it should just write the "b" component of the in-memory
array to the file.
Werner
On 22.07.2016 21:29, Aman Verma wrote:
Werner,
Thanks for responding. I understand what you’re saying and had
tried it before. During dataset creation, I replaced mtype (Class’
type) with mElementType (let’s say float). This leads to runtime
errors.
H5::CompTypemtype(sizeof(Class));
mtype.insertMember("MD", HOFFSET(Class, dMD), datatype);
H5::DataSetdataset = solution.createDataSet( "/Well",
mElementType, dataspace, ds_creatplist );
dataset.write( ObjectArray, mtype );
Further on, during the dataset write, I now substitute:
dataset.write( ObjectArray, mElementType );
This too leads to some complaining. However, the file is written
out but with junk/wrong values. I am not surprised at this
behavior given what I’m doing. However, I wonder if there is a way
to release the unused space.
Again, for simplicity, let’s say I only want to write out the
element bfrom an array of the struct
typedefstructs1_t {
int a;
float b;
doublec;
} s1_t[LENGTH];
How can I achieve this without doing:
s1_tid = H5Tcreate (H5T_COMPOUND, sizeof(s1_t));
which leads to the file size being on the order of
sizeof(s1_t)instead of sizeof(float))?
Appreciate your time.
Aman
*From:*Hdf-forum [mailto:[email protected]] *On
Behalf Of *Werner Benger
*Sent:* Friday, July 22, 2016 9:58 AM
*To:* [email protected]
<mailto:[email protected]>
*Subject:* Re: [Hdf-forum] [Ext] Re: Writing subset of compound
datatype
Hi Aman,
no, you don't copy anything. You reference your full data
structure and describe it with the complete memory layout of your
data structure, but in the file you use a different data type.
Currently you are using "mtype" in both the creation of the
dataset and when writing the data, so in file you get the same as
in memory. But you dont want that, you want to create a dataset
that contains only a part of your data structure, so during data
set creation time you would use a different type, not "mtype".
Werner
On 22.07.2016 16:07, Aman Verma wrote:
Hi Werner,
I guess what you’re implying is that I copy the components
being written to file (Element belonging to ObjectArray[i]) to
a different, more appropriate datatype such as an array:
ElementTemp[i]. However I want to avoid doing this copying at
every time step. There also doesn’t seem a way to make a
reference to this data, else I could just use that to write.
What am I missing here?
Aman
*From:*Hdf-forum [mailto:[email protected]]
*On Behalf Of *Werner Benger
*Sent:* Friday, July 22, 2016 7:58 AM
*To:* [email protected]
<mailto:[email protected]>
*Subject:* [Ext] Re: [Hdf-forum] Writing subset of compound
datatype
Hi,
you probably want a different datatype in the file than in
memory, i.e. in memory you want a datatype that describes the
entire class, but for the file type one that only refers to
the components written.
Werner
On 22.07.2016 00:22, Aman Verma wrote:
I want to write, in a single line, the elements:
ObjectArray[i].Element (0<=i<n) without having to copy the
elements into a separate array altogether.
Using CompType and insertMember, I am writing just a
subset (including Element) of an array of a compound
datatype ObjectArray (a class/object in my case).
H5::CompTypemtype(sizeof(Class));
mtype.insertMember("MD", HOFFSET(Class, dMD), datatype);
H5::DataSetdataset = solution.createDataSet( "/Well",
mtype, dataspace, ds_creatplist );
dataset.write( ObjectArray, mtype );
This works fine. However, not unexpectedly, since I am
defining the CompType with the size of the whole class
(Class), while writing out only a subset (Element), my .h5
file is bigger (sizeof(Class)) than it should be
(sizeof(Element)). I am already using compression. Is
there a way to ‘delete’ this unused space? Or is there a
better way to do what I’m trying to achieve? Is using
hyperslab the right answer?
Thanks
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___________________________________________________________________________
Dr. Werner Benger Visualization Research
Center for Computation & Technology at Louisiana State University
(CCT/LSU)
2019 Digital Media Center, Baton Rouge, Louisiana 70803
Tel.: +1 225 578 4809 Fax.: +1 225 578-5362
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Hdf-forum is for HDF software users discussion.
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___________________________________________________________________________
Dr. Werner Benger Visualization Research
Center for Computation & Technology at Louisiana State University (CCT/LSU)
2019 Digital Media Center, Baton Rouge, Louisiana 70803
Tel.: +1 225 578 4809 Fax.: +1 225 578-5362
_______________________________________________
Hdf-forum is for HDF software users discussion.
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___________________________________________________________________________
Dr. Werner Benger Visualization Research
Center for Computation & Technology at Louisiana State University (CCT/LSU)
2019 Digital Media Center, Baton Rouge, Louisiana 70803
Tel.: +1 225 578 4809 Fax.: +1 225 578-5362
_______________________________________________
Hdf-forum is for HDF software users discussion.
[email protected]
http://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org
Twitter: https://twitter.com/hdf5
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___________________________________________________________________________
Dr. Werner Benger Visualization Research
Center for Computation & Technology at Louisiana State University (CCT/LSU)
2019 Digital Media Center, Baton Rouge, Louisiana 70803
Tel.: +1 225 578 4809 Fax.: +1 225 578-5362
_______________________________________________
Hdf-forum is for HDF software users discussion.
[email protected]
http://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org
Twitter: https://twitter.com/hdf5
