Void callback subscriber does not work [closed]

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Hi Ros users

i would like to send odometry (just linear and angular velocity) to another IP via socket udp.

But I have a problem. The problem is that void velsubcallback is not executed and I do not why.. (The catkin_make is ok)

This is my .cpp and my int main (but i think we have to focus on while):

 void velsubcallback(const nav_msgs::Odometry& msg)
   {  
    variable1=msg.twist.twist.linear.x;
    variable2=msg.twist.twist.angular.z;
 lectura_ros.linear=variable1;
 lectura_ros.angular=variable2;
         ROS_INFO("variable %f",lectura_ros.linear);        
       }

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

int va_send_to;
int long_dir_cli;
int socket_ros; 
struct sockaddr_in dir_serv_socket,dir_cli_socket;
  ros::init(argc, argv, "lanzando_vel");
  ros::NodeHandle n;
    while (ros::ok())
      {

      ros::Subscriber odom_sub = n.subscribe("p3dx/odom", 1000, velsubcallback);

    va_send_to = sendto(socket_ros,(char *)&lectura_ros,sizeof(dato_ros),0,(struct sockaddr *)&dir_cli_socket,sizeof(dir_cli_socket));

Any idea??

Thank you so much!