ROS学习笔记：用C++编写一个简单的服务和客户端

这一节主要介绍如何使用c++编写一个简单的服务和客户端节点。

编写服务节点

由于在前面的练习中，已经向beginner_tutorials软件包中复制了一个addtwoints.srv文件。所以这里直接在src目录中创建add_two_ints_server.cpp文件即可。

#include "ros/ros.h"
#include "beginner_tutorials/addtwoints.h"   //在devel/include目录中，由addtwoints.srv文件自动生成的

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);
  //一旦检测到有add_two_ints服务，就调用add函数
  ros_info("ready to add two ints.");
  ros::spin();

  return 0;
}

编写客户端节点

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

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("add_two_ints");
  //生成一个add_two_ints服务
  beginner_tutorials::addtwoints srv;
  srv.request.a = atoll(argv[1]);
  srv.request.b = atoll(argv[2]);
  //将char转换为int，atoll函数位于cstdlib库文件中
  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;
}

编译节点

要修改cmakelists.txt文件，在文件中添加如下代码：

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)

然后在catkin工作空间中运行

catkin_make

检验服务与客户端

确认在每个终端中都载入了工作空间的环境变量之后，在三个不同的终端中运行如下三行代码：

roscore
rosrun beginner_tutorials add_two_ints_server
rosrun beginner_tutorials add_two_ints_client 1 5

如下图所示