C++ publisher and subscriber

Step 1

Set up

cd ~/robot_ws/src
ros2 pkg create --build-type ament_cmake --license Apache-2.0 robot_topics --dependencies rclcpp std_msgs

Step 2

Create the file

class JointPublisher : public rclcpp::Node {
public:
  JointPublisher() : Node("joint_publisher") {
    pub_ = create_publisher<std_msgs::msg::Float64>("joint_target", 10);
    timer_ = create_wall_timer(std::chrono::milliseconds(100), [this] {
      std_msgs::msg::Float64 msg; msg.data = target_;
      pub_->publish(msg); target_ += 0.01;
    });
  }
private:
  double target_{0.0};
  rclcpp::Publisher<std_msgs::msg::Float64>::SharedPtr pub_;
  rclcpp::TimerBase::SharedPtr timer_;
};

Step 3

Build, run and inspect

colcon build --packages-select robot_topics --symlink-install
source install/setup.bash
ros2 run robot_topics joint_publisher
# Second terminal:
ros2 topic echo /joint_target
ros2 topic hz /joint_target

• Source the same overlay in every terminal.
• Use ros2 topic info /joint_target --verbose to compare publisher and subscriber QoS.