ROS C++ - Ⅱ

ROS publisher and subscriber nodes using C++

Step 1: Set Up Your ROS Workspace - Before you create nodes, make sure you have a ROS workspace set up. If you don’t have one, you can create it using the following commands:

mkdir -p ~/catkin_ws/src
cd ~/catkin_ws/
catkin_make

Step 2: Create a ROS Package

• Inside the src directory of your ROS workspace, create a new ROS package. Replace my_cpp_package with your desired package name:

  cd ~/catkin_ws/src
  catkin_create_pkg my_cpp_package roscpp std_msgs
  

Step 3: Create the Publisher Node

• Navigate to your package directory:

  cd ~/catkin_ws/src/my_cpp_package
  

• Create a source file for the publisher node. For example, publisher_node.cpp:

  #include <ros/ros.h>
  #include <std_msgs/String.h>
  
  int main(int argc, char** argv) {
      // Initialize ROS
      ros::init(argc, argv, "publisher_node");
  
      // Create a ROS node handle
      ros::NodeHandle nh;
  
      // Create a publisher for the "my_topic" topic
      ros::Publisher pub = nh.advertise<std_msgs::String>("my_topic", 10);
  
      // Set the publishing rate
      ros::Rate rate(1);
  
      // Main loop
      while (ros::ok()) {
          // Create a message
          std_msgs::String msg;
          msg.data = "Hello, ROS Publisher!";
  
          // Publish the message
          pub.publish(msg);
  
          // Sleep to maintain the publishing rate
          rate.sleep();
      }
  
      return 0;
  }
  

Step 4: Create the Subscriber Node

• Create another source file for the subscriber node. For example, subscriber_node.cpp:

  #include <ros/ros.h>
  #include <std_msgs/String.h>
  
  // Callback function to process incoming messages
  void messageCallback(const std_msgs::String::ConstPtr& msg) {
      ROS_INFO("Received: %s", msg->data.c_str());
  }
  
  int main(int argc, char** argv) {
      // Initialize ROS
      ros::init(argc, argv, "subscriber_node");
  
      // Create a ROS node handle
      ros::NodeHandle nh;
  
      // Create a subscriber for the "my_topic" topic with the callback function
      ros::Subscriber sub = nh.subscribe("my_topic", 10, messageCallback);
  
      // Spin to receive messages
      ros::spin();
  
      return 0;
  }
  

Step 5: Update CMakeLists.txt

• Open the CMakeLists.txt file in your package directory and add the following lines to configure the build for both the publisher and subscriber nodes:

  add_executable(publisher_node src/publisher_node.cpp)
  target_link_libraries(publisher_node ${catkin_LIBRARIES})
  
  add_executable(subscriber_node src/subscriber_node.cpp)
  target_link_libraries(subscriber_node ${catkin_LIBRARIES})
  

Step 6: Build and Run

• Build your package using catkin_make:

  cd ~/catkin_ws
  catkin_make
  

• Source the setup script:

  source devel/setup.bash
  

• Now you can run the publisher and subscriber nodes in separate terminal windows:

  • Terminal 1 (for the publisher node):

    rosrun my_cpp_package publisher_node
    

  • Terminal 2 (for the subscriber node):

    rosrun my_cpp_package subscriber_node
    

• You should see the subscriber printing the messages published by the publisher.