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Creating Groups {#tutorial_hdf_create_groups}
===============================
Goal
----
This tutorial will show you:
- How to create a HDF5 file?
- How to create a group?
- How to check whether a given group exists or not?
- How to create a subgroup?
Source Code
----
The following code creates two groups: `Group1` and `SubGroup1`, where
`SubGroup1` is a child of `Group1`.
You can download the code from [here][1] or find it in the file
`modules/hdf/samples/create_groups.cpp` of the opencv_contrib source code library.
@snippet samples/create_groups.cpp tutorial
Explanation
----
First, we create a HDF5 file
@snippet samples/create_groups.cpp tutorial_create_file
If the given file does not exist, it will be created. Otherwise, it is open for read and write.
Next, we create the group `Group1`
@snippet samples/create_groups.cpp tutorial_create_group
Note that we have to check whether `/Group1` exists or not using
the function cv::hdf::HDF5::hlexists() before creating it. You can not create
a group with an existing name. Otherwise, an error will occur.
Then, we create the subgroup named `Subgroup1`. In order to
indicate that it is a sub group of `Group1`, we have to
use the group name `/Group1/SubGroup1`:
@snippet samples/create_groups.cpp tutorial_create_subgroup
Note that before creating a subgroup, we have to make sure
that its parent group exists. Otherwise, an error will occur.
In the end, we have to close the file
@snippet samples/create_groups.cpp tutorial_close_file
Result
----
There are many tools that can be used to inspect a given HDF file, such
as HDFView and h5dump. If you are using Ubuntu, you can install
them with the following commands:
@code
sudo apt-get install hdf5-tools hdfview
@endcode
There are also binaries available from the The HDF Group official website <https://support.hdfgroup.org/HDF5/Tutor/tools.html>.
The following figure shows the result visualized with the tool HDFView:
The output for `h5dump` is:
@code
$ h5dump mytest.h5
HDF5 "mytest.h5" {
GROUP "/" {
GROUP "Group1" {
GROUP "SubGroup1" {
}
}
}
}
@endcode
[1]: https://github.com/opencv/opencv_contrib/tree/master/modules/hdf/samples/create_groups.cpp
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