How can I subscribe to a turtle's pose that is being published?

edit

I am working on Indigo turtlesim and I am making a turtle move randomly.

This is how I am publishing the pose of a turtle which is randomly moving.

#include "ros/ros.h"
#include "geometry_msgs/Twist.h"
#include "geometry_msgs/Pose.h"
#include <sstream>


using namespace std;

int main(int argc, char **argv)
{

 // Initiate new ROS node named "pub1"
 ros::init(argc, argv, "pub1");
 ros::NodeHandle n;

 ros::Publisher velocity_publisher = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel", 1000);
 ros::Rate loop_rate(1); //1 message per second

   int count = 0;
   /* initialize random seed: */
   srand (time(NULL));
   while (ros::ok()) // Keep spinning loop until user presses Ctrl+C
   {

   geometry_msgs::Twist vel_msg;
   //set a random linear velocity in the x-axis
   vel_msg.linear.x =(double)(rand() % 10 + 1)/4.0;
   vel_msg.linear.y =0;
   vel_msg.linear.z =0;
   //set a random angular velocity in the y-axis
   vel_msg.angular.x = 0;
   vel_msg.angular.y = 0;
   vel_msg.angular.z =(double)(rand() % 10 - 5)/2.0;

   //print the content of the message in the terminal
   ROS_INFO("[Random Walk] linear.x = %.2f, angular.z=%.2f\n, %d", vel_msg.linear.x, vel_msg.angular.z, count);

   //publish the message
   velocity_publisher.publish(vel_msg);
   ros::spinOnce(); // Need to call this function often to allow ROS to process incoming messages

   loop_rate.sleep(); // Sleep for the rest of the cycle, to enforce the loop rate
   count++;
    }
   return 0;
}

And this is how I am trying to subscribe to the "velocity_msg" thing. But unfortunately it is not printing anything probably that is not getting subscribed to the pose.

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

/**
 * This tutorial demonstrates simple receipt of messages over the ROS system.
 */
void chatterCallback(const std_msgs::String::ConstPtr& vel_msg)
{
  ROS_INFO("%s", vel_msg->data.c_str());
}

int main(int argc, char **argv)
{
  /**
   * The ros::init() function needs to see argc and argv so that it can perform
   * any ROS arguments and name remapping that were provided at the command line.
   * For programmatic remappings you can use a different version of init() which takes
   * remappings directly, but for most command-line programs, passing argc and argv is
   * the easiest way to do it.  The third argument to init() is the name of the node.
   *
   * You must call one of the versions of ros::init() before using any other
   * part of the ROS system.
   */
  ros::init(argc, argv, "listener");

  /**
   * NodeHandle is the main access point to communications with the ROS system.
   * The first NodeHandle constructed will fully initialize this node, and the last
   * NodeHandle destructed will close down the node.
   */
   ros::NodeHandle n;

  /**
   * The subscribe() call is how you tell ROS that you want to receive messages
   * on a given topic.  This invokes a call to the ROS
   * master node, which keeps a registry of who is publishing and who
   * is subscribing.  Messages are passed to a callback function, here
   * called chatterCallback.  subscribe() returns a Subscriber object that you
   * must hold on to until you want to unsubscribe.  When all copies of the Subscriber
   * object go out of scope, this callback will automatically be unsubscribed from
   * this ...