pub.publish(...) won't work [closed]

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I am currently trying to learn how to use a laser scanner and point clouds, and I wrote code that should convert a laser scan message into a point cloud. Everything seems to work fine. My node subscribes to the /scan topic, and the laser scan data is converted to a point cloud. The problem is when I try to publish. When I make the call to pub.publisher (pub is the name of my publisher object), nothing happens. If I try to echo the /scan_cloud topic (the one I'm publishing to), nothing appears. Here is my code:

#include <ros/ros.h>
#include <sensor_msgs/PointCloud.h>
#include <laser_geometry/laser_geometry.h>
#include <tf/transform_listener.h>

laser_geometry::LaserProjection projector;
sensor_msgs::PointCloud _cloud;
bool firstMsg = 0;

void convert(const sensor_msgs::LaserScan::ConstPtr &scan) {
  sensor_msgs::PointCloud cloud;
  tf::TransformListener listener;
  projector.projectLaser(*scan, cloud);
  _cloud = cloud;
  firstMsg = 1;
}

int main(int argc, char **argv) {
  ros::init(argc, argv, "scan_test");
  ros::NodeHandle nh;
  ros::Subscriber sub = nh.subscribe("scan", 1000, convert);
  ros::Publisher pub = nh.advertise<sensor_msgs::PointCloud>("scan_cloud", 1000);
  ros::Rate loop_rate(10);
  while (ros::ok()) {
    std::cout << _cloud << std::endl;
    pub.publish(_cloud);
    ros::spinOnce();
    loop_rate.sleep();
  };
  return 0;
}

Thanks.