ROS 消息通訊——發布者/訂閱者的來龍去脈

• 創建工作空間和工作環境

mkdir -p ~/learning_ws/src  //工作環境及功能包建立、編譯
cd ~/learning_ws/    
catkin_make    
source devel/setup.bash    //設置環境變量
echo $ROS_PACKAGE_PATH    
cd ~/learning_ws/src
catkin_create_pkg ros_tutorials_topic message_generation std_msgs roscpp //創建功能包和依賴

 

 

•  修改配置文件package.xml

<?xml version="1.0"?>
<package format="2">
  <name>ros_tutorials_topic</name>
  <version>0.1.0</version>
  <description>The ros_tutorials_topic package</description>
  <maintainer email="[e-mail]">Fuzhuoxin</maintainer> 
<license>Apache License 2.0</license> 
<author email="[e-mail]">Fuzhuoxin</author> 
<buildtool_depend>catkin</buildtool_depend> 
<build_depend>message_generation</build_depend> 
<build_depend>roscpp</build_depend> 
<build_depend>std_msgs</build_depend> 
<build_export_depend>roscpp</build_export_depend> 
<build_export_depend>std_msgs</build_export_depend> 
<exec_depend>roscpp</exec_depend> 
<exec_depend>std_msgs</exec_depend> 
<export></export> 
</package>

//注釋解釋內容如下，在工程中不可直接復制，用上面無注釋版
 1 <!-- xml版本聲明 -->
<?xml version="1.0"?>
<!-- 功能包標簽 -->
<package format="2">
    <!-- 功能包名稱 -->
  <name>ros_tutorials_topic</name>
    <!-- 功能包版本 -->
  <version>0.0.0</version>
    <!-- 功能包簡要說明 -->
  <description>The ros_tutorials_topic package</description>
    <!-- 功能包管理者信息 -->
  <maintainer email="[e-mail]">tianbot</maintainer>
    <!-- 記錄版本許可 -->
  <license>Apache License 2.0</license>
  <!-- 功能包說明的詳細地址、網頁、博客等 -->
  <!-- <url type="website">https://www.cnblogs.com/fuzhuoxin/</url> -->
  <!-- 開發人員信息 -->
  <!-- <author email="[e-mail]">Jane Doe</author> -->
    <!-- 構建系統依賴關系，正在使用catkin構建 -->
  <buildtool_depend>catkin</buildtool_depend>
    <!-- 編寫功能包時所依賴的功能包名稱 -->
  <build_depend>message_generation</build_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>std_msgs</build_depend>
  <build_export_depend>roscpp</build_export_depend>
  <build_export_depend>std_msgs</build_export_depend>
  <exec_depend>roscpp</exec_depend>
  <exec_depend>std_msgs</exec_depend>
  <export></export>
</package>

配置CMake文件：

#版本要求
cmake_minimum_required(VERSION 2.8.3)
#工程名字
project(ros_tutorials_topic)
#添加依賴包message_generation  roscpp  std_msgs
find_package(catkin REQUIRED COMPONENTS
  message_generation
  roscpp
  std_msgs
)
#聲明msg文件夾下的消息文件MsgTutorial.msg
add_message_files(
   FILES 
   MsgTutorial.msg
 )
#設置依賴性消息
generate_messages(
   DEPENDENCIES
   std_msgs
 )
#catkin功能包選項，描述庫、catkin構建依賴項和系統依賴的功能包
catkin_package(

  LIBRARIES ros_tutorials_topic
  CATKIN_DEPENDS roscpp std_msgs
)
#設置包含目錄
include_directories(
  ${catkin_INCLUDE_DIRS}
)
#配置可執行文件、目標鏈接庫和其他依賴性
add_executable(topic_publisher src/topic_publisher.cpp)
add_dependencies(topic_publisher ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
target_link_libraries(topic_publisher ${catkin_LIBRARIES})

#配置可執行文件、目標鏈接庫和其他依賴性
add_executable(topic_subscriber src/topic_subscriber.cpp)
add_dependencies(topic_subscriber ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
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

 

 

內容為

time stamp
int32 data
string speak

 

• 創建發布者節點：對應CMakeLists.txt中添加的add_executable(topic_publisher src/topic_publisher.cpp) 

 

 

 

 內容為：

#include <ros/ros.h>
#include <ros_tutorials_topic/MsgTutorial.h> //MsgTutorial消息頭文件（構建后自動生成）


int main(int argc,char **argv)
{
ros::init(argc,argv,"topic_publisher"); //初始化發布者節點名稱
ros::NodeHandle nh;//聲明節點句柄與ROS系統進行通訊
//聲明發布者，創建一個使用ros_tutorials_topic功能包MsgTutorial消息文件的發布者
//ros_tutorial_pub,話題名稱是ros_tutorial_msg，消息發布者隊列設置為100
ros::Publisher ros_tutorial_pub = nh.advertise<ros_tutorials_topic::MsgTutorial>("ros_tutorial_msg", 100);
ros::Rate loop_rate(10);//設定循環周期10HZ，0.1秒
ros_tutorials_topic::MsgTutorial msg;//聲明一個消息
int count = 0;
std::stringstream talk;
while(ros::ok())
{
msg.stamp = ros::Time::now();//給MsgTutorial.msg文件中的消息變量賦值
msg.data = count;
talk << "How are you"<< count;
msg.speak = talk.str();
ROS_INFO("send msg = %d",msg.stamp.sec);//顯示消息
ROS_INFO("send msg = %d",msg.stamp.nsec);
ROS_INFO("send msg = %d",msg.data);
ROS_INFO("%s",msg.speak.c_str());
ros_tutorial_pub.publish(msg);//發布顯示的消息
ros::spinOnce();//循環等待訂閱節點的所有回調函數
loop_rate.sleep();    //按設定值循環    
++count;
}
return 0;
}

• 創建發布者節點：對應CMakeLists.txt中添加的add_executable(topic_publisher src/topic_publisher.cpp)

 

 

 內容為：

#include <ros/ros.h>
#include <ros_tutorials_topic/MsgTutorial.h>

//回調函數
void msgCallback(const ros_tutorials_topic::MsgTutorial::ConstPtr& msg)
{
ROS_INFO("recieve msg = %d",msg->stamp.sec);
ROS_INFO("recieve msg = %d",msg->stamp.nsec);
ROS_INFO("recieve msg = %d",msg->data);
ROS_INFO("I receive you say:[%s]",msg->speak.c_str());
}
int main(int argc,char **argv)
{
ros::init(argc,argv,"topic_subscriber");//初始化訂閱者節點
ros::NodeHandle nh;
//聲明訂閱者，創建一個使用ros_tutorials_topic功能包MsgTutorial消息文件的訂閱者
//ros_tutorial_sub，訂閱的話題名稱是ros_tutorial_msg，消息接收者隊列設置為100
ros::Subscriber ros_tutorial_sub = nh.subscribe<ros_tutorials_topic::MsgTutorial>("ros_tutorial_msg", 100, msgCallback);
ros::spin();//調用后台，等待接收消息 
return 0; 21 }

運行效果：

 

 命令查看節點關系如圖所示：與程序的對應關系為

ros::init(argc,argv,"topic_publisher"); //初始化發布者節點名稱

話題名稱是ros_tutorial_msg

ros::init(argc,argv,"topic_subscriber");//初始化訂閱者節點

 

命令運行rostopic echo /ros_tutorial_msg，查看話題發布的消息，可以看到消息是連續發布的，只要建立了聯系，不會中斷，一直發布。

 

 　　用rqt插件同樣可以監控話題的消息內容