Topic creation and running example of ROS

Reference resources
ROS official wiki— establish ROS Messages and services
ROS official wiki— Write simple publishers and subscribers （C++）
ROS official wiki— Verify simple publishers and subscribers

Pre blog post
ROS Logical view of
ROS Working space for

Definition of message

First, enter the created package

$ roscd beginner_tutorials
$ mkdir srv

Message definition file (*.msg)

Define a string message

$ echo "int64 num" > msg/Num.msg

Set up *.msg File compilation information
stay packages.xml Add the configuration

  <build_depend>message_generation</build_depend> #  Compile time dependent Libraries 
  <exec_depend>message_runtime</exec_depend>      #  Runtime dependent Libraries 

stay CMakeLists.txt Make the following settings in

#  add to ROS Dependency Library 
find_package(catkin REQUIRED COMPONENTS
   roscpp
   rospy
   std_msgs		#  Standard information , Basic data supported by the system , Such as int,float,...
   message_generation #  take *.srv The file to C++/Python Code 
                      #  stay  packages.xml  Has added 
)

#  Add just written *.msg file 
add_message_files(  # ROS  Defined cmake command , inform ROS Custom files 
   FILES
   Num.msg
)
# ROS  Defined cmake command , inform ROS Generate (C++/Python) Message class dependency Library 
generate_messages(  
  DEPENDENCIES
  std_msgs
)

View the generated msg Information

# rosmsg show [message type]
$ rosmsg show beginner_tutorials/Num

msg Any... In the directory .msg Files will generate code for all supported languages .
- C++ The header file of the message will be generated in ~/catkin_ws/devel/include/beginner_tutorials/.
- Python The script will be created in ~/catkin_ws/devel/lib/python2.7/dist-packages/beginner_tutorials/msg.

Publisher code

github Code original website

#include "ros/ros.h" // ROS  The header file 
#include "std_msgs/String.h" //  System defined string messages 

#include <sstream>

int main(int argc, char **argv)
{
    
  //  The first two command line arguments 
  //  The third node name , Node names cannot conflict ！！！
  ros::init(argc, argv, "talker");

  // ROS  System handle 
  //  The first to apply for resources , The last handle destroys all requested resources 
  ros::NodeHandle n;

  //  The first parameter ,Topic Name ,roscore The publisher will be assigned to the corresponding subscriber by name , Then the two communicate point-to-point 
  //  The second parameter ,Topic  Cache size of , Those in excess will be discarded 
  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);

  //  With  10 Hz  Frequency of news release 
  ros::Rate loop_rate(10);

  while (ros::ok())
  {
    
    std_msgs::String msg; //  Message object 

    std::stringstream ss;
    ss << "hello world " << count;
    msg.data = ss.str();

    ROS_INFO("%s", msg.data.c_str());

    //  Release the news 
    chatter_pub.publish(msg);

    //  Used to receive messages from other publishers , It can be omitted here 
    ros::spinOnce();

    loop_rate.sleep();
  }
  return 0;
}

Subscriber code

github Sample code

#include "ros/ros.h"
#include "std_msgs/String.h"

//  Callback function , How to handle the received message 
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
    
  ROS_INFO("I heard: [%s]", msg->data.c_str());
}

int main(int argc, char **argv)
{
    
   //  The first two command line arguments 
  //  The third node name , Node names cannot conflict ！！！
  ros::init(argc, argv, "listener");

  ros::NodeHandle n;
  
  //  The first parameter , The name of the publisher 
  //  The second parameter , Number of cached messages 
  //  The third parameter , Callback function for processing messages 
  ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);

  //  Call the message callback function upon receiving the message 
  //  once ros::ok() return false,ros::spin() You're going to quit 
  ros::spin();

  return 0;
}

Build the program

following cmake The script beginner_tutorials_generate_messages_cpp see

cmake_minimum_required(VERSION 2.8.3)
project(beginner_tutorials)

find_package(catkin REQUIRED COMPONENTS roscpp rospy std_msgs genmsg)

##  Declare as  catkin package
catkin_package()

include_directories(include ${catkin_INCLUDE_DIRS})

#  Publisher  talker
add_executable(talker src/talker.cpp)
target_link_libraries(talker ${catkin_LIBRARIES})
add_dependencies(talker beginner_tutorials_generate_messages_cpp) # add_dependencies  yes ROS Defined commands 

#  subscriber  listener
add_executable(listener src/listener.cpp)
target_link_libraries(listener ${catkin_LIBRARIES})
add_dependencies(listener beginner_tutorials_generate_messages_cpp) # add_dependencies  yes ROS Defined commands 

Created executable talker and listener, By default, it will be placed in the package directory devel In the space , namely ~/catkin_ws/devel/lib/<package name>.

If you add a new package , You may need to specify –force-cmake Parameters to make catkin Force generation . See Use the workspace .

Verify the compiled program

$ cd ~/catkin_ws
$ catkin_make  #  Compile code 
$ roscore # ROS System 
$ source ./devel/setup.bash  #  Every time  catkin_make  After execution 

Start publisher talker

$ rosrun beginner_tutorials talker      # (C++)

You can see messages like the following ：

[INFO] [WallTime: 1314931831.774057] hello world 1314931831.77
[INFO] [WallTime: 1314931832.775497] hello world 1314931832.77

Start the subscriber listener

$ rosrun beginner_tutorials listener     # (C++)

You can see messages like the following ：

[INFO] [WallTime: 1314931969.258941] /listener_17657_1314931968795I heard hello world 1314931969.26
[INFO] [WallTime: 1314931970.262246] /listener_17657_1314931968795I heard hello world 1314931970.26