Topic model

The picture below is from Gu Yue's "21 Lectures on ROS Introduction"

ROS Master manages two nodes, the publisher turtlesim and the subscriber Pose Listener communicate through the /turtle1/pose topic transmission turtlesim::Pose type messages, this section mainly implements the subscriber Subscriber

Create subscriber code (C++)

Introduce the header file

#include <ros/ros.h>
#include <turtlesim/Pose.h>
//引入消息类型头文件

Main function

int main(int argc, char **argv)
{
    
    
	//初始化ROS节点
	ros::init(argc, argv, "pose_subscriber");
	
	//创建节点句柄
	ros::NodeHandle n;
	
	//创建一个subscriber，订阅名为/turtle1/pose的topic，注册回调函数poseCallback
	ros::Subscriber pose_sub = n.subscribe("/turtle1/pose", 10, poseCallback);
	
	//循环等待回调函数
	ros::spin();
	
	return 0;
}

Callback

void poseCallback(const turtlesim::Pose::ConstPtr& msg)
{
    
    
	//将接收到的消息打印出来
	ROS_INFO("Turtle pose : x:%0.6f, y:%.6f", msg->x, msg->y);
}

Complete code

/**
 * 该例程将订阅/turtle1/pose话题，消息类型为turtlesim::Pose
 */
 
#include <ros/ros.h>
#include <turtlesim/Pose.h>
//引入消息类型头文件

//接收到订阅消息后，会进入回调函数
void poseCallback(const turtlesim::Pose::ConstPtr& msg)
{
    
    
	//将接收到的消息打印出来
	ROS_INFO("Turtle pose : x:%0.6f, y:%.6f", msg->x, msg->y);
}

int main(int argc, char **argv)
{
    
    
	//初始化ROS节点
	ros::init(argc, argv, "pose_subscriber");
	
	//创建节点句柄
	ros::NodeHandle n;
	
	//创建一个subscriber，订阅名为/turtle1/pose的topic，注册回调函数poseCallback
	ros::Subscriber pose_sub = n.subscribe("/turtle1/pose", 10, poseCallback);
	
	//循环等待回调函数
	ros::spin();
	
	return 0;
}

Process combing

Initialize the ROS node
Create subscribers, subscribe to the required topics
Wait for the topic message in a loop, and enter the callback function after receiving the message
Complete message processing in the callback function

Configure subscriber code compilation rules

The same as the configuration method in Note 5:
Use:

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

Set the code to be compiled and the executable file generated
Set up the link library

Compile and run the subscriber

$ cd~/catkin_ws
$ catkin_make
$ source devel/setup.bash
$ roscore
$ rosrun turtlesim turtlesim_node
$ rosrun learning_topic velocity_publisher
$ rosrun learning_topic pose_subscriber

You can observe the output result:
Insert picture description here

Subscriber code (Python)

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# 该例程将订阅/turtle1/pose话题，消息类型turtlesim::Pose

import rospy
from turtlesim.msg import Pose

def poseCallback(msg):
    rospy.loginfo("Turtle pose: x:%0.6f, y:%0.6f", msg.x, msg.y)

def pose_subscriber():
	# ROS节点初始化
    rospy.init_node('pose_subscriber', anonymous=True)

	# 创建一个Subscriber，订阅名为/turtle1/pose的topic，注册回调函数poseCallback
    rospy.Subscriber("/turtle1/pose", Pose, poseCallback)

	# 循环等待回调函数
    rospy.spin()

if __name__ == '__main__':
    pose_subscriber()

Part of the code in this article comes from Gu Yue "21 Lectures on ROS Introduction"

Previous link

ROS study notes 5 (programming implementation of Publisher Publisher)
ROS study notes 4 (create workspace and function package)
ROS study notes 3 (use of ROS command line tools)
ROS study notes 2 (ROS core concepts)
ROS study notes 1 (Basic operation of Linux system)

ROS Study Notes 6 (Programming Implementation of Subscriber)

ROS study notes six