Problem publishing at cmd_vel

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Hello,

I have written the following code so I can send commands to my robots motors, which are listening to the /labrob/cmd_vel topic:

#include "ros/ros.h"
#include "geometry_msgs/Twist.h"

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

  ros::init(argc, argv,"vel");
  ros::NodeHandle vel;
  ros::Publisher vel_pub = vel.advertise<geometry_msgs::Twist>("/labrob/cmd_vel", 100);
  ros::Rate loop_rate(10);
    geometry_msgs::Twist msg;
    msg.linear.x = 0.1;
    msg.linear.y = 0;
    msg.linear.z = 0;
    msg.angular.x = 0;
    msg.angular.y = 0;
    msg.angular.z = 0;
    vel_pub.publish(msg);
    ros::spin();

  return 0;
}

With the rostopic pub command via the terminal, I can move the robot fine, but with the code I posted, the robot does not respond. What I am doing wrong ?