You're reading the documentation for an older, but still supported, version of ROS 2. For information on the latest version, please have a look at Humble.
ROS 2 Client Interfaces (Client Libraries)
The ROS Client Library for C++ (
rclcpp) is the user facing, C++ idiomatic interface which provides all of the ROS client functionality like creating nodes, publisher, and subscribers.
rclcpp builds on top of
rcl and the
rosidl API, and it is designed to be used with the C++ messages generated by
rclcpp makes use of all the features of C++ and C++11 to make the interface as easy to use as possible, but since it reuses the implementation in
rcl it is able maintain a consistent behavior with the other client libraries that use the
The ROS Client Library for Python (
rclpy) is the Python counterpart to the C++ client library.
Like the C++ client library,
rclpy also builds on top of the
rcl C API for its implementation.
The interface provides an idiomatic Python experience which uses native Python types and patterns like lists and context objects, but by using the
rcl API in the implementation it stays consistent with the other client libraries in terms of feature parity and behavior.
In addition to providing Python idiomatic bindings around the
rcl API and Python classes for each message, the Python client library takes care of the execution model, using
threading.Thread or similar to run the functions in the
Like C++ it generates custom Python code for each ROS message that the user interacts with, but unlike C++ it eventually converts the native Python message object into the C version of the message.
All operations happen on the Python version of the messages until they need to be passed into the
rcl layer, at which point they are converted into the plain C version of the message so it can be passed into the
rcl C API.
This is avoided if possible when communicating between publishers and subscribers in the same process to cut down on the conversion into and out of Python.