Creating ROS2 Action in C++

Below are the steps to create a ROS2 action. Notice that we are going to have two packages involved: 1) a package called “my_package” which contains the action file, and 2) a package called “action_nodes_cpp” which contains the action server and client nodes. Separating the package which contains the action file(s) like this, in general, is a good practice.

Step 1: Creating an action file.

Create a folder called “action” (if you still don’t have it) inside a package folder called “my_package”. And then make the action file (.action) called “ActionFile.action”. For example, if the action is to compute Fibonacci numbers, you may call it “Fibonacci.action” which looks like below:

The lines of three dashes above separate between the request variable(s), the result variable(s), and the feedback variable(s).

Step 2: Add the following in package.xml

Step 3: Add the following in CMakeLists.txt, before ament_package().

Step 4: Write the “action_server” node.

Write the action_server node in a file namely “my_action_server.cpp”, inside “src” folder of the package.

Step 5: Write the “action_client” node.

Write the action_client node in a file namely “my_action_client.cpp”, inside “src” folder of the package.

Example of action_server and action_client nodes in C++ can be found here: https://docs.ros.org/en/foxy/Tutorials/Actions/Writing-a-Cpp-Action-Server-Client.html#actionscpp

Step 6: Build the package by using “colcon build” command.

Running the action

Type the following in the terminal to run the “action_server” node:

Type the following in the terminal to run the “action_client” node:

To show the stream of the action feedback:

Official documentation:

• https://docs.ros.org/en/foxy/Tutorials/Actions/Creating-an-Action.html
• https://docs.ros.org/en/foxy/Tutorials/Actions/Writing-a-Cpp-Action-Server-Client.html#actionscpp