Subscriber and Publisher node at once in cpp

edit

i need some an example how to wrtie a node, wich is subscribing and publishing at the same time. I want to publish a message when i got i message, beacuse of that i try to publish in the Callback function, but it doesn't work.

My code is following:

void pointCallback(const nxt_msgs::Range  &msg)
{
         sensor_msgs::LaserScan pub;
         ros::NodeHandle r;
         ros::Publisher laser_scan_pub = r.advertise<sensor_msgs::LaserScan>("laser_scan", 50);
         laser_scan_pub.publish(pub);
}
int main(int argc, char **argv)
{

 ros::init(argc, argv, "range_to_laser");
 ros::NodeHandle n;
 ros::Subscriber sub = n.subscribe("point_cloud", 50, pointCallback);
 ros::spin();

 return 0;
}