ROS study notes 7 - writing a simple server and client (C++)

1 Premise

Create AddTwoInts.srv in the /catkin_ws/src/beginner_tutorials/srv directory

  1 int64 a
  2 int64 b
  3 ---
  4 int64 sum

2 Write the server node

[~/catkin_ws/src/beginner_tutorials]$ vim src/add_two_ints_server.cpp

The contents of add_two_ints_server.cpp are as follows:

  1 #include "ros/ros.h"
  2 /* is the corresponding header file automatically generated by the compiler system according to the srv file created by the user*/
  3 #include "beginner_tutorials/AddTwoInts.h"
  4
  5 bool add(beginner_tutorials::AddTwoInts::Request &req,
  6          beginner_tutorials::AddTwoInts::Response &res)
  7 {
  8     res.sum = req.a + req.b;
  9     ROS_INFO("request: x=%ld, y=%ld", (long int)req.a, (long int)req.b);
 10     ROS_INFO("sending back response: [%ld]", (long int)res.sum);
 11     return true;
 12 }
 13
 14
 15 int main(int argc, char **argv)
 16 {
 17     ros::init(argc, argv, "add_two_ints_server");
 18     ros::NodeHandle n;
 19 /* Create a server and publish it in ros*/
 20     ros::ServiceServer service = n.advertiseService("add_two_ints", add);
 21     ROS_INFO("Ready to add two ints.");
 22     ros::spin();
 23
 24     return 0;
 25 }
 26

3 Write the client node

[~/catkin_ws/src/beginner_tutorials]$ vim src/add_two_ints_client.cpp

The contents of add_two_ints_client.cpp are as follows:

  1 #include "ros/ros.h"
  2 #include "beginner_tutorials/AddTwoInts.h"
  3 #include <cstdlib>
  4
  5
  6 int main(int argc,char **argv)
  7 {
  8     ros::init(argc, argv, "add_two_ints_client");
  9     if(argc != 3)
 10     {
 11          ROS_INFO("usage: add_two_ints_client");
 12          return 1;
 13     }
 14
 15     ros::NodeHandle n;
 16     ros::ServiceClient client = n.serviceClient<beginner_tutorials::AddTwoIn    ts>("add_two_ints");
 17     beginner_tutorials::AddTwoInts srv;
 18     srv.request.a = atoll(argv[1]);
 19     srv.request.b = atoll(argv[2]);
 20     if(client.call(srv))
 21     {
 22         ROS_INFO("Sum: %ld", (long int)srv.response.sum);
 23     }
 24     else
 25     {
 26          ROS_INFO("Failed to call service add_two_ints");
 27          return 1;
 28     }
 29
 30     return 0;
 31
 32
 33 }
 34
 35

4 Compile

Modify the CMakeLists.txt file and add at the end of the file

211
212 add_executable(add_two_ints_server src/add_two_ints_server.cpp)
213 target_link_libraries(add_two_ints_server ${catkin_LIBRARIES})
214 add_dependencies(add_two_ints_server beginner_tutorials_gencpp)
215
216 add_executable(add_two_ints_client src/add_two_ints_client.cpp)
217 target_link_libraries(add_two_ints_client ${catkin_LIBRARIES})
218 add_dependencies(add_two_ints_client beginner_tutorials_gencpp)

compile

[~/catkin_ws]$ catkin_make

5 Verify

runService

rosrun beginner_tutorials add_two_ints_server

Start another terminal and run the Client

rosrun beginner_tutorials add_two_ints_client 1 3

The service side shows:

Client display

ROS study notes 7 - writing a simple server and client (C++)

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