vendor: OpenCV 5.0.0 snapshot at 755e50675d97db9b7d449d8bd6b09888646f6c6e

modules/hdf/tutorials/read_write_attributes/read_write_attributes.markdown

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+Reading and Writing Attributes{#tutorial_hdf_read_write_attributes}
+===============================
+
+Goal
+----
+This tutorial shows you:
+ - How to write attributes?
+ - How to read attributes?
+
+@note Although attributes can be associated with groups and datasets, only attributes
+with the root group are implemented in OpenCV. Supported attribute types are
+`int`, `double`, `cv::String` and `cv::InputArray` (only for continuous arrays).
+
+Source Code
+----
+
+The following code demonstrates reading and writing attributes
+inside the root group with data types `cv::Mat`, `cv::String`, `int`
+and `double`.
+
+You can download the code from [here][1] or find it in the file
+`modules/hdf/samples/read_write_attributes.cpp` of the opencv_contrib source code library.
+
+@snippet samples/read_write_attributes.cpp tutorial
+
+Explanation
+----
+
+The first step is to open the HDF5 file:
+
+@snippet samples/read_write_attributes.cpp tutorial_open_file
+
+Then we use cv::hdf::HDF5::atwrite() to write attributes by specifying its value and name:
+
+@snippet samples/read_write_attributes.cpp tutorial_write_mat
+
+@warning Before writing an attribute, we have to make sure that
+the attribute does not exist using cv::hdf::HDF5::atexists().
+
+To read an attribute, we use cv::hdf::HDF5::atread() by specifying the attribute name
+
+@snippet samples/read_write_attributes.cpp tutorial_read_mat
+
+In the end, we have to close the HDF file
+
+@snippet samples/read_write_attributes.cpp tutorial_close_file
+
+Results
+----
+
+Figure 1 and Figure 2 give the results visualized using the tool HDFView.
+
+![Figure 1: Attributes of the root group](pics/attributes-file.png)
+
+![Figure 2: Detailed attribute information](pics/attributes-details.png)
+
+[1]: https://github.com/opencv/opencv_contrib/tree/master/modules/hdf/samples/read_write_attributes.cpp