C++ ROS Publisher

Introduction

In ROS (Robot Operating System), a publisher is a node that sends messages to a topic. Messages are a way for nodes to communicate with each other. In this tutorial, we will learn how to create a C++ ROS publisher node that publishes a string message to a topic.

Prerequisites

Before we begin, make sure you have the following:

• A working ROS installation
• Basic knowledge of C++

Steps

1. Create a new package: navigate to your ROS workspace directory and run the command catkin_create_pkg pub_node roscpp std_msgs. This will create a new package called pub_node with dependencies on roscpp and std_msgs.

2. Create a new file called publisher.cpp inside the src directory of pub_node. This file will contain the code for our publisher node.

3. Open publisher.cpp and include the necessary headers:

   #include <ros/ros.h>
   #include <std_msgs/String.h>
   

4. Declare the main function and create a ROS node handle:

   int main(int argc, char **argv)
   {
       ros::init(argc, argv, "publisher_node");
       ros::NodeHandle nh;
       // code for the publisher node
       return 0;
   }
   

   The ros::init() function initializes the ROS system and the ros::NodeHandle object provides a way to interface with the ROS system.

5. Create a publisher object that publishes messages of type std_msgs::String:

   ros::Publisher pub = nh.advertise<std_msgs::String>("chatter", 1000);
   

   Here, the advertise() function creates a publisher object that sends messages to the chatter topic with a buffer size of 1000 messages.

6. Create a loop that publishes the message:

   ros::Rate loop_rate(10);
   while (ros::ok())
   {
       std_msgs::String msg;
       msg.data = "Hello, world!";
       pub.publish(msg);
   
       ros::spinOnce();
   
       loop_rate.sleep();
   }
   

   This loop publishes the message "Hello, world!" to the chatter topic at a rate of 10 Hz.

7. Save and close the file.

8. Build the package: navigate to the root of your ROS workspace directory and run the command catkin_make.

9. Source the setup file: run the command source devel/setup.bash to set up the environment variables for the package.

10. Start the ROS master: run the command roscore.

11. Open a new terminal and run the publisher node: run the command rosrun pub_node publisher_node.

12. You should see the message "Hello, world!" printed in the terminal every 0.1 seconds (10 Hz).

Conclusion

In this tutorial, we learned how to create a C++ ROS publisher node that publishes a string message to a topic. We covered the necessary steps to create a ROS package, create a publisher object, and publish messages to the topic. With this knowledge, you can now build more complex ROS systems that involve multiple nodes communicating with each other.