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

If some errors occur, try erasing the msg and srv folders again and follow the setup from this earlier tutorial. Then just follow the directions on this page for building the server, client, and nodes.