Creating C++ Nodes (for :program:`ament_cmake`) =============================================== .. admonition:: The C++ binary block for :program:`ament_cmake` .. dropdown:: TL;DR When adding a new Node in an existing :file:`CMakeLists.txt`, you might benefit from using the following template. Remember to: #. Add **ALL** dependencies (including ROS2 ones) with ``find_package``, if applicable. .. literalinclude:: ../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/CMakeLists.txt :language: cmake :lines: 8-10 #. Change ``print_forever_node`` to the name of your Node. #. Add all source files to ``add_executable``. #. Add all ROS2 dependencies of this binary to ``ament_target_dependencies``. #. Add any other (**NOT ROS2**) libraries to ``target_link_libraries``. .. literalinclude:: ../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/CMakeLists.txt :language: cmake :lines: 12-47 :emphasize-lines: 7,12,17,21 Create the package ------------------ .. warning:: We'll skip using the ``--node-name`` option to create the Node template, because, currently, it generates a Node and a :file:`CMakeLists.txt` different from my advice. .. code-block:: console cd ~/ros2_tutorial_workspace/src ros2 pkg create cpp_package_with_a_node \ --build-type ament_cmake \ --dependencies rclcpp which outputs .. dropdown:: ros2 pkg create output .. code-block:: console :emphasize-lines: 13-16 going to create a new package package name: cpp_package_with_a_node destination directory: /home/murilo/ROS2_Tutorial/ros2_tutorial_workspace/src package format: 3 version: 0.0.0 description: TODO: Package description maintainer: ['murilo '] licenses: ['TODO: License declaration'] build type: ament_cmake dependencies: ['rclcpp'] creating folder ./cpp_package_with_a_node creating ./cpp_package_with_a_node/package.xml creating source and include folder creating folder ./cpp_package_with_a_node/src creating folder ./cpp_package_with_a_node/include/cpp_package_with_a_node creating ./cpp_package_with_a_node/CMakeLists.txt [WARNING]: Unknown license 'TODO: License declaration'. This has been set in the package.xml, but no LICENSE file has been created. It is recommended to use one of the ament license identitifers: Apache-2.0 BSL-1.0 BSD-2.0 BSD-2-Clause BSD-3-Clause GPL-3.0-only LGPL-3.0-only MIT MIT-0 Package-related sources ----------------------- .. admonition:: In this step, we'll work on these. .. code-block:: console :emphasize-lines: 2,6 cpp_package_with_a_node ├── CMakeLists.txt ├── include │   └── cpp_package_with_a_node │   └── .placeholder ├── package.xml └── src ├── print_forever_node.cpp ├── print_forever_node.hpp └── print_forever_node_main.cpp The files already exist, we just need to modify them as follows .. tab-set:: .. tab-item:: package.xml The :file:`package.xml` works the same way as in :program:`ament_python`, with the exception of the two lines about :program:`ament_cmake` shown below. :download:`package.xml <../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/package.xml>` .. literalinclude:: ../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/package.xml :language: xml :linenos: :emphasize-lines: 10,18 .. tab-item:: CMakeLists.txt A *one-size-fits-most* solution is shown below. For each new Node we add a block to the :file:`CMakeLists.txt` with the following format. :download:`CMakeLists.txt <../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/CMakeLists.txt>` .. literalinclude:: ../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/CMakeLists.txt :language: cmake :linenos: :emphasize-lines: 12-47 Making C++ ROS2 Nodes --------------------- .. admonition:: (Murilo's) ``rclcpp`` best practices For each new C++ Node, we make three files following the style below. For a Node called ``print_forever_node`` we have #. :file:`src/print_forever_node.hpp` with the Node's class definition. In general, this is not exported to other packages, so it should not be in the package's :file:`include` folder. #. :file:`src/print_forever_node.cpp` with the Node's class implementation. #. :file:`src/print_forever_node_main.cpp` with the Node's main function implementation. .. admonition:: In this step, we'll work on these. .. code-block:: console :emphasize-lines: 7-10 cpp_package_with_a_node ├── CMakeLists.txt ├── include │   └── cpp_package_with_a_node │   └── .placeholder ├── package.xml └── src ├── print_forever_node.cpp ├── print_forever_node.hpp └── print_forever_node_main.cpp These files do not exist, so we'll create them. .. tab-set:: .. tab-item:: folder Create the folder. .. code-block:: console cd ~/ros2_tutorial_workspace/src/cpp_package_with_a_node mkdir src .. tab-item:: src/..._node.hpp Similar to what we did in Python, we inherit from ``rclcpp::Node``. Whatever is different is owing to differences in languages. :download:`print_forever_node.hpp <../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/src/print_forever_node.hpp>` .. literalinclude:: ../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/src/print_forever_node.hpp :language: cpp :linenos: :lines: 24- :emphasize-lines: 9 .. tab-item:: src/..._node.cpp The implementation has nothing special, just don't forget to initialize the parent class, ``rclcpp::Node``, with the name of the node. :download:`print_forever_node.cpp <../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/src/print_forever_node.cpp>` .. literalinclude:: ../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/src/print_forever_node.cpp :language: cpp :linenos: :lines: 24- :emphasize-lines: 7 .. tab-item:: src/..._main.cpp Given that we are using ``rclcpp::spin()``, there is nothing special here either. Just remember to not mess up the ``std::make_shared`` and always use perfect forwarding. The ``rclcpp::spin()`` handles the ``SIGINT`` when we, for example, press :kbd:`CTRL+C` on the terminal. It is not perfect, but it does the trick for simple nodes like this one. :download:`print_forever_node_main.cpp <../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/src/print_forever_node_main.cpp>` .. literalinclude:: ../../../ros2_tutorial_workspace/src/cpp_package_with_a_node/src/print_forever_node_main.cpp :language: cpp :linenos: :lines: 24- :emphasize-lines: 11 Add a :file:`.placeholder` if your :file:`include/` is empty -------------------------------------------------------------------------- .. warning:: If you don't do this and add this package as a git repository without any files on the :file:`include/`, :program:`CMake` might return with an error when trying to compile your package. .. code-block:: console :emphasize-lines: 5 cpp_package_with_a_node ├── CMakeLists.txt ├── include │   └── cpp_package_with_a_node │   └── .placeholder ├── package.xml └── src ├── print_forever_node.cpp ├── print_forever_node.hpp └── print_forever_node_main.cpp Empty directories will `not be tracked by git `_. A file has to be added to the index. We can create an empty file in the :file:`include` folder as follows .. code-block:: console cd ~/ros2_tutorial_workspace/src/cpp_package_with_a_node/src touch include/cpp_package_with_a_node/.placeholder Running a C++ Node ------------------ As simple as it has always been, see :ref:`Running a node`. .. code-block:: console ros2 run cpp_package_with_a_node print_forever_node which returns .. code-block:: console [INFO] [1688620414.406930812] [print_forever_node]: Printed 0 times. [INFO] [1688620414.906890884] [print_forever_node]: Printed 1 times. [INFO] [1688620415.406907619] [print_forever_node]: Printed 2 times. [INFO] [1688620415.906881003] [print_forever_node]: Printed 3 times. [INFO] [1688620416.406900108] [print_forever_node]: Printed 4 times. [INFO] [1688620416.906886691] [print_forever_node]: Printed 5 times. [INFO] [1688620417.406881803] [print_forever_node]: Printed 6 times. [INFO] [1688620417.906858551] [print_forever_node]: Printed 7 times. [INFO] [1688620418.406894922] [print_forever_node]: Printed 8 times. and we'll use :kbd:`CTRL+C` to stop the node, resulting in .. code-block:: console [INFO] [1688620418.725674401] [rclcpp]: signal_handler(signum=2)