编写简单的Service和Client

编写Service节点

节点名叫：add_two_ints_server。先把目录转到beginner_tutorials 
在src文件夹下面新建add_two_ints_server.cpp 。复制代码

#include "ros/ros.h"
#include "beginner_tutorials/AddTwoInts.h"

bool add(beginner_tutorials::AddTwoInts::Request &req, beginner_tutorials::AddTwoInts::Request &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;
}

add()函数提供相加两个整数的服务，参数是srv文件中定义的request和reponse类型 ros::ServiceServer service = n.advertiseService(“add_two_ints”,add);建立service，发布

编写Client节点

同样新建add_two_ints_clients.cpp，复制代码。

#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_clients 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;
}

beginner_tutorials::AddTwoInts srv;
  srv.request.a = atoll(argv[1]);
  srv.request.b = atoll(argv[2]);

这里实例化一个由ROS编译系统自动生成的service类，并给其request成员赋值。一个service类包含两个成员request和response。同时也包括两个类定义Request和Response

if(client.call(srv))

这里调用service，当它被调用时其他服务是被阻止的，调用完成返回true，失败返回false

编译节点

  add_executable(add_two_ints_server src/add_two_ints_server.cpp)
target_link_libraries(add_two_ints_server ${catkin_LIBRARIES})
add_dependencies(add_two_ints_server beginner_tutorials_gencpp)

add_executable(add_two_ints_client src/add_two_ints_client.cpp)
target_link_libraries(add_two_ints_client ${catkin_LIBRARIES})
add_dependencies(add_two_ints_client beginner_tutorials_gencpp)

将以上贴到CMakeLists.txt。增加两个可执行文件（node类似等于可执行文件） 然后catkin_make