Publishers

Creating a Publisher Node

Basic steps:

1. Create a node.

2. Create a publisher object on a given topic.

3. Publish messages periodically (for example, using a timer).

Example Publisher (C++)

#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"

class MinimalPublisher : public rclcpp::Node
{
public:
  MinimalPublisher()
    : Node("minimal_publisher")
  {
    publisher_ = this->create_publisher<std_msgs::msg::String>("chatter", 10);

    timer_ = this->create_wall_timer(
      std::chrono::milliseconds(500),
      std::bind(&MinimalPublisher::timer_callback, this));
  }

private:
  void timer_callback()
  {
    auto msg = std::make_unique<std_msgs::msg::String>();
    msg->data = "Hello ROS 2";
    RCLCPP_INFO(this->get_logger(), "Publishing: '%s'", msg->data.c_str());
    publisher_->publish(std::move(msg));
  }

  rclcpp::Publisher<std_msgs::msg::String>::SharedPtr publisher_;
  rclcpp::TimerBase::SharedPtr timer_;
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<MinimalPublisher>());
  rclcpp::shutdown();
  return 0;
}

Key Parameters

• Topic name: “chatter” in this example.

• Queue size: 10 – affects buffering and QoS behavior.

Testing the Publisher

After building and sourcing:

ros2 run my_package minimal_publisher
ros2 topic echo /chatter