Getting native type of HDF5 attribute

Hdf-forum archives
1

Hi,

I am using Visual Studio (C#) and HDF5 P/Invoke.

I have made an HDF5 file with groups and datasets with attributes of
different datatypes (in this case, let's say it is an integer, saved as
H5T.NATIVE_INT32, but I have the same problem for other datatypes). Now I
am making a code to read data from the HDF5 file. To read the attribute
value, I first need to determine the data type of the attribute value. I
have tried the following:

attributeId = H5A.open(groupId, attributeName, H5P.DEFAULT);
hid_t attributeSpace = H5A.get_space(attributeId);
H5S.class_t extentType = H5S.get_simple_extent_type(attributeSpace);
hid_t typeId = H5A.get_type(attributeId);
attributeClass = H5T.get_class(typeId);
type = H5T.get_native_type(typeId, H5T.direction_t.DEFAULT);
H5T.close(typeId);

However, the resulting variable type does not match with the
H5T.NATIVE_INTEGER type, or any other H5T type I can think of. In fact, even

H5T.get_native_type(H5T.NATIVE_INT, H5T.direction_t.DEFAULT) ==
H5T.NATIVE_INT

returns false, so it appears as if H5T.get_native_type() does not return a
type, but perhaps a copy or a pointer of it, which is not identical to the
type itself. Is this expected behaviour or a bug? How do I correctly figure
out the type of an attribute value?

Best regards,
Johan Lindberg

2

Johan, the only valid way to compare the underlying types of two datatype handles (identifiers)
is H5Tequal (or H5T.equal in HDF.PInvoke)

https://support.hdfgroup.org/HDF5/doc/RM/RM_H5T.html#Datatype-Equal

Most likely, you will narrow down the type by first establishing the datatype’s “class”
via H5Tget_class (H5T.get_class), and then refine your test from there.

The HDF5 API handles, including datatype IDs, are opaque and transient, and don’t mean anything
as integer values.

G.

···

From: Hdf-forum [mailto:hdf-forum-bounces@lists.hdfgroup.org] On Behalf Of Johan Lindberg
Sent: Monday, May 22, 2017 4:23 AM
To: hdf-forum@lists.hdfgroup.org
Subject: [Hdf-forum] Getting native type of HDF5 attribute

Hi,

I am using Visual Studio (C#) and HDF5 P/Invoke.

I have made an HDF5 file with groups and datasets with attributes of different datatypes (in this case, let's say it is an integer, saved as H5T.NATIVE_INT32, but I have the same problem for other datatypes). Now I am making a code to read data from the HDF5 file. To read the attribute value, I first need to determine the data type of the attribute value. I have tried the following:

attributeId = H5A.open(groupId, attributeName, H5P.DEFAULT);
hid_t attributeSpace = H5A.get_space(attributeId);
H5S.class_t extentType = H5S.get_simple_extent_type(attributeSpace);
hid_t typeId = H5A.get_type(attributeId);
attributeClass = H5T.get_class(typeId);
type = H5T.get_native_type(typeId, H5T.direction_t.DEFAULT);
H5T.close(typeId);

However, the resulting variable type does not match with the H5T.NATIVE_INTEGER type, or any other H5T type I can think of. In fact, even

H5T.get_native_type(H5T.NATIVE_INT, H5T.direction_t.DEFAULT) == H5T.NATIVE_INT

returns false, so it appears as if H5T.get_native_type() does not return a type, but perhaps a copy or a pointer of it, which is not identical to the type itself. Is this expected behaviour or a bug? How do I correctly figure out the type of an attribute value?

Best regards,
Johan Lindberg

3

Thanks for the quick reply, Gerd! That is exactly what I needed.

Best,
Johan

···

2017-05-22 15:24 GMT+02:00 Gerd Heber <gheber@hdfgroup.org>:

Johan, the only valid way to compare the underlying types of two datatype
handles (identifiers)

is H5Tequal (or H5T.equal in HDF.PInvoke)

https://support.hdfgroup.org/HDF5/doc/RM/RM_H5T.html#Datatype-Equal

Most likely, you will narrow down the type by first establishing the
datatype’s “class”

via H5Tget_class (H5T.get_class), and then refine your test from there.

The HDF5 API handles, including datatype IDs, are opaque and transient,
and don’t mean anything

as integer values.

G.

*From:* Hdf-forum [mailto:hdf-forum-bounces@lists.hdfgroup.org] *On
Behalf Of *Johan Lindberg
*Sent:* Monday, May 22, 2017 4:23 AM
*To:* hdf-forum@lists.hdfgroup.org
*Subject:* [Hdf-forum] Getting native type of HDF5 attribute

Hi,

I am using Visual Studio (C#) and HDF5 P/Invoke.

I have made an HDF5 file with groups and datasets with attributes of
different datatypes (in this case, let's say it is an integer, saved as
H5T.NATIVE_INT32, but I have the same problem for other datatypes). Now I
am making a code to read data from the HDF5 file. To read the attribute
value, I first need to determine the data type of the attribute value. I
have tried the following:

attributeId = H5A.open(groupId, attributeName, H5P.DEFAULT);

hid_t attributeSpace = H5A.get_space(attributeId);

H5S.class_t extentType = H5S.get_simple_extent_type(attributeSpace);

hid_t typeId = H5A.get_type(attributeId);

attributeClass = H5T.get_class(typeId);

type = H5T.get_native_type(typeId, H5T.direction_t.DEFAULT);

H5T.close(typeId);

However, the resulting variable type does not match with the
H5T.NATIVE_INTEGER type, or any other H5T type I can think of. In fact, even

H5T.get_native_type(H5T.NATIVE_INT, H5T.direction_t.DEFAULT) ==
H5T.NATIVE_INT

returns false, so it appears as if H5T.get_native_type() does not return a
type, but perhaps a copy or a pointer of it, which is not identical to the
type itself. Is this expected behaviour or a bug? How do I correctly figure
out the type of an attribute value?

Best regards,

Johan Lindberg

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