ROS 消息通讯——发布者/订阅者的来龙去脉

创建工作空间和工作环境

1 mkdir -p ~/learning_ws/src  //工作环境及功能包建立、编译
2 cd ~/learning_ws/    
3 catkin_make    
4 source devel/setup.bash    //设置环境变量
5 echo $ROS_PACKAGE_PATH    
6 cd ~/learning_ws/src
7 catkin_create_pkg ros_tutorials_topic message_generation std_msgs roscpp //创建功能包和依赖

修改配置文件package.xml

 1 <?xml version="1.0"?>
 2 <package format="2">
 3   <name>ros_tutorials_topic</name>
 4   <version>0.1.0</version>
 5   <description>The ros_tutorials_topic package</description>
 6   <maintainer email="tianbot@todo.todo">Fuzhuoxin</maintainer> 
 7 <license>Apache License 2.0</license> 
 8 <author email="tianbot@todo.todo">Fuzhuoxin</author> 
 9 <buildtool_depend>catkin</buildtool_depend> 
10 <build_depend>message_generation</build_depend> 
11 <build_depend>roscpp</build_depend> 
12 <build_depend>std_msgs</build_depend> 
13 <build_export_depend>roscpp</build_export_depend> 
14 <build_export_depend>std_msgs</build_export_depend> 
15 <exec_depend>roscpp</exec_depend> 
16 <exec_depend>std_msgs</exec_depend> 
17 <export></export> 
18 </package>

//注释解释内容如下，在工程中不可直接复制，用上面无注释版
 1 <!-- xml版本声明 -->
 2 <?xml version="1.0"?>
 3 <!-- 功能包标签 -->
 4 <package format="2">
 5     <!-- 功能包名称 -->
 6   <name>ros_tutorials_topic</name>
 7     <!-- 功能包版本 -->
 8   <version>0.0.0</version>
 9     <!-- 功能包简要说明 -->
10   <description>The ros_tutorials_topic package</description>
11     <!-- 功能包管理者信息 -->
12   <maintainer email="tianbot@todo.todo">tianbot</maintainer>
13     <!-- 记录版本许可 -->
14   <license>Apache License 2.0</license>
15   <!-- 功能包说明的详细地址、网页、博客等 -->
16   <!-- <url type="website">https://www.cnblogs.com/fuzhuoxin/</url> -->
17   <!-- 开发人员信息 -->
18   <!-- <author email="jane.doe@example.com">Jane Doe</author> -->
19     <!-- 构建系统依赖关系，正在使用catkin构建 -->
20   <buildtool_depend>catkin</buildtool_depend>
21     <!-- 编写功能包时所依赖的功能包名称 -->
22   <build_depend>message_generation</build_depend>
23   <build_depend>roscpp</build_depend>
24   <build_depend>std_msgs</build_depend>
25   <build_export_depend>roscpp</build_export_depend>
26   <build_export_depend>std_msgs</build_export_depend>
27   <exec_depend>roscpp</exec_depend>
28   <exec_depend>std_msgs</exec_depend>
29   <export></export>
30 </package>

配置CMake文件：

 1 #版本要求
 2 cmake_minimum_required(VERSION 2.8.3)
 3 #工程名字
 4 project(ros_tutorials_topic)
 5 #添加依赖包message_generation  roscpp  std_msgs
 6 find_package(catkin REQUIRED COMPONENTS
 7   message_generation
 8   roscpp
 9   std_msgs
10 )
11 #声明msg文件夹下的消息文件MsgTutorial.msg
12 add_message_files(
13    FILES 
14    MsgTutorial.msg
15  )
16 #设置依赖性消息
17 generate_messages(
18    DEPENDENCIES
19    std_msgs
20  )
21 #catkin功能包选项，描述库、catkin构建依赖项和系统依赖的功能包
22 catkin_package(
23 
24   LIBRARIES ros_tutorials_topic
25   CATKIN_DEPENDS roscpp std_msgs
26 )
27 #设置包含目录
28 include_directories(
29   ${catkin_INCLUDE_DIRS}
30 )
31 #配置可执行文件、目标链接库和其他依赖性
32 add_executable(topic_publisher src/topic_publisher.cpp)
33 add_dependencies(topic_publisher ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
34 target_link_libraries(topic_publisher ${catkin_LIBRARIES})
35 
36 #配置可执行文件、目标链接库和其他依赖性
37 add_executable(topic_subscriber src/topic_subscriber.cpp)
38 add_dependencies(topic_subscriber ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
39 target_link_libraries(topic_subscriber ${catkin_LIBRARIES})

在CMakeLists.txt中添加了add_message_files( FILES MsgTutorial.msg)因此要包含MsgTutorial.msg文件

内容为

1 time stamp
2 int32 data
3 string speak

创建发布者节点：对应CMakeLists.txt中添加的add_executable(topic_publisher src/topic_publisher.cpp)

内容为：

 1 #include <ros/ros.h>
 2 #include <ros_tutorials_topic/MsgTutorial.h> //MsgTutorial消息头文件（构建后自动生成）
 3 
 4 
 5 int main(int argc,char **argv)
 6 {
 7 ros::init(argc,argv,"topic_publisher"); //初始化发布者节点名称
 8 ros::NodeHandle nh;//声明节点句柄与ROS系统进行通讯
 9 //声明发布者，创建一个使用ros_tutorials_topic功能包MsgTutorial消息文件的发布者
10 //ros_tutorial_pub,话题名称是ros_tutorial_msg，消息发布者队列设置为100
11 ros::Publisher ros_tutorial_pub = nh.advertise<ros_tutorials_topic::MsgTutorial>("ros_tutorial_msg", 100);
12 ros::Rate loop_rate(10);//设定循环周期10HZ，0.1秒
13 ros_tutorials_topic::MsgTutorial msg;//声明一个消息
14 int count = 0;
15 std::stringstream talk;
16 while(ros::ok())
17 {
18 msg.stamp = ros::Time::now();//给MsgTutorial.msg文件中的消息变量赋值
19 msg.data = count;
20 talk << "How are you"<< count;
21 msg.speak = talk.str();
22 ROS_INFO("send msg = %d",msg.stamp.sec);//显示消息
23 ROS_INFO("send msg = %d",msg.stamp.nsec);
24 ROS_INFO("send msg = %d",msg.data);
25 ROS_INFO("%s",msg.speak.c_str());
26 ros_tutorial_pub.publish(msg);//发布显示的消息
27 ros::spinOnce();//循环等待订阅节点的所有回调函数
28 loop_rate.sleep();    //按设定值循环    
29 ++count;
30 }
31 return 0;
32 }

创建发布者节点：对应CMakeLists.txt中添加的add_executable(topic_publisher src/topic_publisher.cpp)

内容为：

 1 #include <ros/ros.h>
 2 #include <ros_tutorials_topic/MsgTutorial.h>
 3 
 4 //回调函数
 5 void msgCallback(const ros_tutorials_topic::MsgTutorial::ConstPtr& msg)
 6 {
 7 ROS_INFO("recieve msg = %d",msg->stamp.sec);
 8 ROS_INFO("recieve msg = %d",msg->stamp.nsec);
 9 ROS_INFO("recieve msg = %d",msg->data);
10 ROS_INFO("I receive you say:[%s]",msg->speak.c_str());
11 }
12 int main(int argc,char **argv)
13 {
14 ros::init(argc,argv,"topic_subscriber");//初始化订阅者节点
15 ros::NodeHandle nh;
16 //声明订阅者，创建一个使用ros_tutorials_topic功能包MsgTutorial消息文件的订阅者
17 //ros_tutorial_sub，订阅的话题名称是ros_tutorial_msg，消息接收者队列设置为100
18 ros::Subscriber ros_tutorial_sub = nh.subscribe<ros_tutorials_topic::MsgTutorial>("ros_tutorial_msg", 100, msgCallback);
19 ros::spin();//调用后台，等待接收消息 
20 return 0; 21 }

运行效果：

命令查看节点关系如图所示：与程序的对应关系为

ros::init(argc,argv,"topic_publisher"); //初始化发布者节点名称

话题名称是ros_tutorial_msg

ros::init(argc,argv,"topic_subscriber");//初始化订阅者节点

命令运行rostopic echo /ros_tutorial_msg，查看话题发布的消息，可以看到消息是连续发布的，只要建立了联系，不会中断，一直发布。

　　用rqt插件同样可以监控话题的消息内容