pubvel.cpp

//this program published randomly-generated velocity
//messages for turtlesim
#include<ros/ros.h>
#include<geometry_msgs/Twist.h>//for geometry_msgs::Twist
#include<stdlib.h> //for rand() and RAND_MAX

int main(int argc,char **argv){
 //initialize the ros system and become a node
ros::init(argc,argv,"publish_velocity");
ros::NodeHandle nh;

//create a publisher object.
ros::Publisher pub =nh.advertise<geometry_msgs::Twist>("turtle1/cmd_vel",1000);

//seed the random number generator
srand(time(0));

//loop at 2HZ until the node is shut down afer 50 times iteration
ros::Rate rate(2);
int i=1;
while(ros::ok()){
//create and fill in the message. the other four
//fields, which are ignored by turtlesim ,default to 0.
geometry_msgs::Twist msg;
msg.linear.x=double(rand())/double(RAND_MAX);
msg.angular.z=2*double(rand())/double(RAND_MAX)-1;

//publish the message
pub.publish(msg);

//send a message to rosout with the details.ROS_INFO_STEAM like the function 'cout ' in c++
ROS_INFO_STREAM("sending random velocity command:"<<"linear="<<msg.linear.x<<"angular="<<msg.angular.z);

//wait until it's time for another iteration
rate.sleep();
i++;
if (i==50) ros::shutdown();
}
}