2.创建订阅者

1、初始化ROS节点
2、订阅需要的话题
3、循环等待话题消息，接受到消息后进行回调函数回调函数中完成消息处理

• 新建listener.cpp文件：
  
• 代码：

#include"ros/ros.h"
#include"std_msgs/String.h"
//接收到订阅的消息，会进入消息的回调函数
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{//将接收到的消息打印处理ROS_INFO("I heard:{%s}",msg->data.c_str());
}
int main(int argc,char **argv)
{setlocale(LC_CTYPE, "zh_CN.utf8");//初始化ROS节点ros::init(argc,argv,"listener");//创建节点句柄ros::NodeHandle n;//创建一个Subscriber，订阅名为chatter的topic，注册回调函数chatterCallbackros::Subscriber sub=n.subscribe("chatter",1000,chatterCallback);//循环等待回调函数ros::spin();return 0;
}

3、修改CMakeLists.txt文件内容

• 在下面位置输入下面的内容：
  

add_executable(talker src/talker.cpp)
target_link_libraries(talker ${catkin_LIBRARIES})
add_executable(listener src/listener.cpp)
target_link_libraries(listener ${catkin_LIBRARIES})

• 键入catkin_make编译：

编译成功！

4、测试

• 打开三个终端测试：

roscore
rosrun learning_communication talker
rosrun learning_communication listener

测试成功！

三、服务编程

1、定义服务请求与应答的方式

• List item
• 创建srv目录及AddTwoInts.srv文件：
  
• AddTwoInts.srv文件内容：

int64 a
int64 b
---
int64 sum

• 在package.xml中添加功能包依赖：

message_generation
message_runtime

• 修改CMakeLists.txt文件内容：

message_generation

CATKIN DEPENDS roscpp rospy std msgs message runtime

add_service_files(FILES  AddTowInts.srv
#   Service1.srv
#   Service2.srv)

2、创建服务端

1、初始化ROS节点
2、创建Serve实例
3、循环等待服务请求，进入回调函数
4、在回调函数中完成服务功能的处理，并反馈应答数据

• server.cpp文件：

#include
#include"learning_communication/AddTwoInts.h"
//service回调函数，输入参数req，输出参数res
bool add(learning_communication::AddTwoInts::Request &req,learning_communication::AddTwoInts::Response &res)
{//将输入的参数中的请求数据相加，结果放到应答变量中res.sum=req.a+req.b;ROS_INFO("request: x=%1d,y=%1d",(long int)req.a,(long int)req.b);ROS_INFO("sending back response:[%1d]",(long int)res.sum);return true;
}
int main(int argc,char **argv)
{//ROS节点初始化ros::init(argc,argv,"add_two_ints_server");//创建节点句柄ros::NodeHandle n;//创建一个名为add_two_ints的server,注册回调函数add()ros::ServiceServer service=n.advertiseService("add_two_ints",add);//循环等待回调函数ROS_INFO("Ready to add two ints.");ros::spin();return 0;
}

3、创建客户端

1、初始化ROS节点
2、创建一个Client实例
3、发布服务请求数据
4、等待Serve处理之后的应答结果

• client.cpp文件：

#include
#include
#include"learning_communication/AddTwoInts.h"
int main(int argc,char **argv)
{//ROS节点初始化ros::init(argc,argv,"add_two_ints_client");//从终端命令行获取两个加数if(argc!=3){ROS_INFO("usage:add_two_ints_client X Y");return 1;}//创建节点句柄ros::NodeHandle n;//创建一个client，请求add_two_ints_service//service消息类型是learning_communication::AddTwoIntsros::ServiceClient client=n.serviceClient("add_two_ints");//创建learning_communication::AddTwoInts类型的service消息learning_communication::AddTwoInts srv;srv.request.a=atoll(argv[1]);srv.request.b=atoll(argv[2]);//发布service请求，等待加法运算的应答请求if(client.call(srv)){ROS_INFO("sum: %1d",(long int)srv.response.sum);}else{ROS_INFO("Failed to call service add_two_ints");return 1;}return 0;
}

• 设置CMakeLists.txt文件：

• 代码：

add_executable(server src/server.cpp)
target_link_libraries(server ${catkin_LIBRARIES})
add_dependencies(server ${PROJECT_NAME}_gencpp)add_executable(client src/client.cpp)
target_link_libraries(client ${catkin_LIBRARIES})
add_dependencies(client ${PROJECT_NAME}_gencpp)

• 编译通过：
  

4、测试

• 开三个终端进行测试：

roscore
rosrun learning_communication server
rosrun learning_communication client 整数1 整数2

• 效果：
  

四、动作编程

• 任务：

客户端发送一个运动坐标，模拟机器人运动到目标位置的过程。包括服务端和客户端的代码实现，要求带有实时位置反馈。

1、新建action文件夹和TurtleMove.action文件

• 代码：

# Define the goal
float64 turtle_target_x  # Specify Turtle's　target position
float64 turtle_target_y
float64 turtle_target_theta
---
# Define the result
float64 turtle_final_x
float64 turtle_final_y
float64 turtle_final_theta
---
# Define a feedback message
float64 present_turtle_x
float64 present_turtle_y
float64 present_turtle_theta

2、 新建turtleMove.cpp服务文件：

• 代码：

/*  此程序通过通过动作编程实现由client发布一个目标位置然后控制Turtle运动到目标位置的过程*/
#include 
#include 
#include "learning_communication/TurtleMoveAction.h"
#include  
#include 
#include typedef actionlib::SimpleActionServer Server;struct Myturtle
{float x;float y;float theta;
}turtle_original_pose,turtle_target_pose;ros::Publisher turtle_vel;void posecallback(const turtlesim::PoseConstPtr& msg) 
{ ROS_INFO("Turtle1_position:(%f,%f,%f)",msg->x,msg->y,msg->theta);turtle_original_pose.x=msg->x; turtle_original_pose.y=msg->y;turtle_original_pose.theta=msg->theta;}// 收到action的goal后调用该回调函数
void execute(const learning_communication::TurtleMoveGoalConstPtr& goal, Server* as)
{learning_communication::TurtleMoveFeedback feedback;ROS_INFO("TurtleMove is working.");turtle_target_pose.x=goal->turtle_target_x;turtle_target_pose.y=goal->turtle_target_y; turtle_target_pose.theta=goal->turtle_target_theta;geometry_msgs::Twist vel_msgs;float break_flag;while(1){  ros::Rate r(10);vel_msgs.angular.z = 4.0 * (atan2(turtle_target_pose.y-turtle_original_pose.y,turtle_target_pose.x-turtle_original_pose.x)-turtle_original_pose.theta);vel_msgs.linear.x = 0.5 * sqrt(pow(turtle_target_pose.x-turtle_original_pose.x, 2) +pow(turtle_target_pose.y-turtle_original_pose.y, 2)); break_flag=sqrt(pow(turtle_target_pose.x-turtle_original_pose.x, 2) +pow(turtle_target_pose.y-turtle_original_pose.y, 2));turtle_vel.publish(vel_msgs);feedback.present_turtle_x=turtle_original_pose.x;feedback.present_turtle_y=turtle_original_pose.y;feedback.present_turtle_theta=turtle_original_pose.theta;as->publishFeedback(feedback);ROS_INFO("break_flag=%f",break_flag);if(break_flag<0.1) break;r.sleep();}// 当action完成后，向客户端返回结果ROS_INFO("TurtleMove is finished.");as->setSucceeded();
}int main(int argc, char** argv)
{ros::init(argc, argv, "TurtleMove");ros::NodeHandle n,turtle_node;ros::Subscriber sub = turtle_node.subscribe("turtle1/pose",10,&posecallback); //订阅小乌龟的位置信息turtle_vel = turtle_node.advertise("turtle1/cmd_vel",10);//发布控制小乌龟运动的速度// 定义一个服务器Server server(n, "TurtleMove", boost::bind(&execute, _1, &server), false);// 服务器开始运行server.start();ROS_INFO("server has started.");ros::spin();return 0;
}

3、新建turtleMoveClient.cpp文件，用于发布位置：

• 代码：

#include 
#include "learning_communication/TurtleMoveAction.h"
#include  
#include 
#include typedef actionlib::SimpleActionClient Client;struct Myturtle
{float x;float y;float theta;
}turtle_present_pose;// 当action完成后会调用该回调函数一次
void doneCb(const actionlib::SimpleClientGoalState& state,const learning_communication::TurtleMoveResultConstPtr& result)
{ROS_INFO("Yay! The TurtleMove is finished!");ros::shutdown();
}// 当action激活后会调用该回调函数一次
void activeCb()
{ROS_INFO("Goal just went active");
}// 收到feedback后调用该回调函数
void feedbackCb(const learning_communication::TurtleMoveFeedbackConstPtr& feedback)
{ROS_INFO(" present_pose : %f  %f  %f", feedback->present_turtle_x,feedback->present_turtle_y,feedback->present_turtle_theta);
}int main(int argc, char** argv)
{ros::init(argc, argv, "TurtleMove_client");// 定义一个客户端Client client("TurtleMove", true);// 等待服务器端ROS_INFO("Waiting for action server to start.");client.waitForServer();ROS_INFO("Action server started, sending goal.");// 创建一个action的goallearning_communication::TurtleMoveGoal goal;goal.turtle_target_x = 1;goal.turtle_target_y = 1;goal.turtle_target_theta = 0;// 发送action的goal给服务器端，并且设置回调函数client.sendGoal(goal,  &doneCb, &activeCb, &feedbackCb);ros::spin();return 0;
}

4、修改CMakeList.txt文件

find_package(catkin REQUIRED COMPONENTSroscpprospystd_msgsmessage_generationactionlib_msgsactionlib
)

add_action_files(FILES TurtleMove.action
)

generate_messages(DEPENDENCIESstd_msgsactionlib_msgs)

add_executable(turtleMoveClient src/turtleMoveClient.cpp)
target_link_libraries(turtleMoveClient ${catkin_LIBRARIES})
add_dependencies(turtleMoveClient ${PROJECT_NAME}_gencpp)
add_executable(turtleMove src/turtleMove.cpp)
target_link_libraries(turtleMove ${catkin_LIBRARIES})
add_dependencies(turtleMove ${PROJECT_NAME}_gencpp)

• 修改package.xml文件：
  

  message_generationactionlibactionlib_msgsmessage_runtimeactionlibactionlib_msgs

• 编译成功：
  

5、测试

依次打开四个终端运行：

roscore
rosrun turtlesim turtlesim_node
rosrun learning_communication turtleMove
rosrun learning_communication turtleMoveClient

五、总结

这里学习了三种通信方式，话题、服务、动作等三种方式，我觉得难度在一级级的增加。通过这次作业，对三种通信方式的具体实现步骤有了更加清晰的了解，尤其对Cmaketext的文件的理解更深入。不足的是这次的分布式通信没有完成，总是出现各种各样的问题、ping不通或者是控制不了，云服务和其他电脑都试过了都不行，等下次看能不能实现在发表博客。

六、参考资料

ROS基础——话题、服务、动作编程