Writing a Simpler Service and Client (C++)

Close all previous terminals. 1) In a terminal, navigate to the beginner_tutorials folder:

  cd ~/catkin_ws/src/beginner_tutorials

2) Check to see if the srv or msg folders exist:

  ls

srv will be listed on the terminal if it exists.

3) If the srv or msg folders exist, use Home Folder and delete either or both folders.

4) Re-create the folder srv:

  mkdir srv

5) Re-create the folder msg:

  mkdir msg

5) Make the following file:

  roscp rospy_tutorials AddTwoInts.srv srv/AddTwoInts.srv

This should create the file AddTwoInts.srv in the srv folder.

6) Create the following file:

  echo "int64 num" > msg/Num.msg

This creates a copy of int64 in the msg folder and names it Num.msg

Writing a Service Node

1) Navigate to the beginner_tutorials folder:

  cd ~/catkin_ws/src/beginner_tutorials

2) Create the file add_two_ints_server.cpp:

  gedit src/add_two_ints_server.cpp

Inside the editor, copy and paste the following:

  #include "ros/ros.h"
   #include "beginner_tutorials/AddTwoInts.h"
   
   bool add(beginner_tutorials::AddTwoInts::Request  &req,
            beginner_tutorials::AddTwoInts::Response &res)
   {
     res.sum = req.a + req.b;
     ROS_INFO("request: x=%ld, y=%ld", (long int)req.a, (long int)req.b);
     ROS_INFO("sending back response: [%ld]", (long int)res.sum);
     return true;
   }
   
   int main(int argc, char **argv)
   {
     ros::init(argc, argv, "add_two_ints_server");
     ros::NodeHandle n;
   
     ros::ServiceServer service = n.advertiseService("add_two_ints", add);
     ROS_INFO("Ready to add two ints.");
     ros::spin();
   
     return 0;
   }

Save the file and close the editor. For information on the code, see this link

Writing a Client Node

1) Navigate to the beginner_tutorials folder:

  cd ~/catkin_ws/src/beginner_tutorials

2) Create the file add_two_ints_client.cpp:

  gedit src/add_two_ints_client.cpp

Inside the editor, copy and paste the following:

  #include "ros/ros.h"
   #include "beginner_tutorials/AddTwoInts.h"
   #include <cstdlib>
   
   int main(int argc, char **argv)
   {
     ros::init(argc, argv, "add_two_ints_client");
     if (argc != 3)
     {
       ROS_INFO("usage: add_two_ints_client X Y");
       return 1;
     }
   
     ros::NodeHandle n;
     ros::ServiceClient client = n.serviceClient<beginner_tutorials::AddTwoInts>("add_two_ints");
     beginner_tutorials::AddTwoInts srv;
     srv.request.a = atoll(argv[1]);
     srv.request.b = atoll(argv[2]);
     if (client.call(srv))
     {
       ROS_INFO("Sum: %ld", (long int)srv.response.sum);
     }
     else
     {
       ROS_ERROR("Failed to call service add_two_ints");
       return 1;
     }
   
     return 0;
   }

Save the file and close the editor. For information on the code, see this link

Building your Nodes

1) Navigate to the beginner_tutorials folder:

  ~/catkin_ws/src/beginner_tutorials

2) Edit the CMakeLists.txt file:

  gedit CMakeLists.txt

Erase the CMakeLists file contents and paste in the contents from this link

3) Navigate to your workspace:

  cd ~/catkin_ws

4) Build your package:

  catkin_make