Subscription a topic from another package

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Below is my code that publishes laser scanner messages and one line that is supposed to subscribe a topic of "pose2D" from another package called laser_scanner_matcher package. I've also referred to the tutorial and am interested to follow what is described in section 2.3.2 using Class Methods, but, it still does not work. Perhaps, one can go to what I've commented out "This subscription does not work" that is needed to be corrected.

#include "ros/ros.h"
#include "std_msgs/String.h"
#include <sstream>
#include <fstream>
#include <sensor_msgs/LaserScan.h>
#include <sensor_msgs/PointCloud.h>
#include <sensor_msgs/PointCloud2.h>
#include "geometry_msgs/Twist.h"
#include "geometry_msgs/Pose.h"
#include "geometry_msgs/PoseStamped.h"
#include <vector>
#include "laser_geometry/laser_geometry.h"
#include <tf/transform_listener.h>
#include <boost/algorithm/string.hpp>
#include "tf/tf.h"
#include "tf/transform_datatypes.h"
#include <tf/transform_broadcaster.h>
// PCL specific includes
#include <pcl/ros/conversions.h>
#include <pcl/point_cloud.h>
#include <pcl/point_types.h>
#include <pcl/filters/voxel_grid.h>
#include <pcl/ros/conversions.h>
#include <pcl/point_cloud.h>
#include <pcl/point_types.h>
#include "pcl/common/angles.h"


using namespace std;


const int num_row = 264;
const int num_column  = 1089;

class PointCloud
{
private:
    ros::NodeHandle n;
//  ros::Publisher chatter_pub;
    ros::Publisher scan_pub;
    ros::Publisher pose_pub;

    int count;
    vector<vector<double> > data_set;


public:
    PointCloud();
    ~PointCloud();

    /**
     * Opens and reads file
     */
    bool operateFile();
    void publishLaser();
//  void display(); //translate and publish

};

    PointCloud::PointCloud()
    {
        scan_pub = n.advertise<sensor_msgs::LaserScan>("/scan", 50);
//      This subscription does not work
        sub = n.subscribe("/pose2D", 1, this);
        count = 0;

    }



    PointCloud::~PointCloud()
    {
        ROS_INFO("Shutting down publisher_node node.");
    }


    /**
     *  @brief Opens and reads file for further processing
     *
     *  @param
     *
     *  @return True if the file is successfully manipulated
     */
    bool PointCloud::operateFile()
    {

        ifstream inFile;  // object for reading from a file
        ofstream outFile; // object for writing to a file
        char inputFilename[] = "/home/alfa/ros_workspace/dataset1.txt";
        inFile.open(inputFilename, ios::in);

        if (!inFile) {
          cerr << "Can't open input file " << inputFilename << endl;
          exit(1);
        }
        else
            cout << "The file is successfully opened :-)" << endl;

        // Set up sizes. (num_row x num_column)
        data_set.resize(num_row);
        for (int i = 0; i < num_row; ++i)
            data_set[i].resize(num_column);

        // Store in a buffer/vector what have been read.
        for (int j = 0; j < num_row; j++)
            for (int k = 0; k < num_column; k++)
            {
                inFile >> data_set[j][k];
            }


        return (true);
    }


    void PointCloud::publishLaser()
    {
        int num_laser_readings;
        double laser_frequency;

        num_laser_readings = 1080;

        laser_frequency = 40; //20 could be


        ros::Rate r(1.0);


        int t = 0;


        while (n.ok() && (t < num_row))
        {
            sensor_msgs::LaserScan scan;


            ros::Time scan_time( double(data_set[t][1]/1000));



            for (int i = 0; i < num_row; i++)
            {
                scan.header.stamp =  scan_time;
            }

            scan.header.frame_id = "laser_frame";
            scan.angle_min = - 270 / 2 * M_PI / 180; // -xx degree
            scan.angle_max = 270 / 2 * M_PI / 180;   // xx degree

            scan.angle_increment = (scan.angle_max-scan.angle_min)/num_laser_readings;

            scan.time_increment = (1 / laser_frequency) / (num_laser_readings);
            scan.range_min = 0.0;
            scan.range_max = 100.0;

            scan.set_ranges_size(num_laser_readings);

            for(int i = 0; i < num_laser_readings; ++i)
            {
//              Laser scanner data reside in column 10th to 1080th
                scan.ranges[i] = data_set[t][i+9] / 1000.0;
            }


            scan_pub.publish(scan);
            ++count;
            ++t;

            r.sleep();
        }
    }



int main(int argc ...