ROS "topic" programming implementation

（ One ） Publisher （publisher） Programming

Create a workspace and compile
Create Feature Pack ：

catkin_create_pkg learning_topic roscpp rospy std_msgs geometry_msgs turtlesim

c++ The code is as follows ：

/**
 *  The routine will publish turtle1/cmd_vel topic of conversation , Message type geometry_msgs::Twist
 */
 
#include <ros/ros.h>
#include <geometry_msgs/Twist.h>

int main(int argc, char **argv)
{
	// ROS Node initialization 
	ros::init(argc, argv, "velocity_publisher");

	//  Create node handle 
	ros::NodeHandle n;

	//  Create a Publisher, The release is called /turtle1/cmd_vel Of topic, The message type is geometry_msgs::Twist, The queue length 10
	ros::Publisher turtle_vel_pub = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel", 10);

	//  Set the frequency of the cycle 
	ros::Rate loop_rate(10);

	int count = 0;
	while (ros::ok())
	{
	    //  initialization geometry_msgs::Twist Type of message 
		geometry_msgs::Twist vel_msg;
		vel_msg.linear.x = 0.5;
		vel_msg.angular.z = 0.2;

	    //  Release the news 
		turtle_vel_pub.publish(vel_msg);
		ROS_INFO("Publsh turtle velocity command[%0.2f m/s, %0.2f rad/s]", 
				vel_msg.linear.x, vel_msg.angular.z);

	    //  Delay according to the cycle frequency 
	    loop_rate.sleep();
	}

	return 0;
}

Return to the root directory of the function package , open cmake.list, stay build Write below ：

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

Open the terminal , Run the following command ：

roscore
rosrun turtlesim turtlesim_node
rosrun learning_topic velocity_publisher

（ Two ） subscriber （subscriber） Programming

The goal is ： Subscribe to turtles pose Information （ Postures ）

c++ The code is as follows ：

/**
 *  This routine will subscribe to /turtle1/pose topic of conversation , Message type turtlesim::Pose
 */
 
#include <ros/ros.h>
#include "turtlesim/Pose.h"

//  After receiving the subscription message , Will enter the message callback function 
void poseCallback(const turtlesim::Pose::ConstPtr& msg)
{
    //  Print the received message 
    ROS_INFO("Turtle pose: x:%0.6f, y:%0.6f", msg->x, msg->y);
}

int main(int argc, char **argv)
{
    //  initialization ROS node 
    ros::init(argc, argv, "pose_subscriber");

    //  Create node handle 
    ros::NodeHandle n;

    //  Create a Subscriber, The subscription is called /turtle1/pose Of topic, Register callback function poseCallback
    ros::Subscriber pose_sub = n.subscribe("/turtle1/pose", 10, poseCallback);

    //  Loop waiting for callback function 
    ros::spin();

    return 0;
}

Return to the root directory of the function package , open cmake.list, stay build Write below ：

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

After compiling , Enter the following command at the terminal ：

roscore
rosrun turtlesim turtlesim_node

We can see , A terminal releases messages , Another subscription message , The turtle is running as shown in the figure ：