Unable to call a publisher function within a subscriber callback.

edit

Am new to ROS, currently trying to call the function that publishes velocity

1. move()

2. stop_moving()

in a subscriber Callback laserCallback

The laserCallback function works when the commented lines // are put in. It doesn't work when the function 1 and 2 is called. Why is this? when they are essentially the same thing.

ros::Publisher chatter_pub;
geometry_msgs::Twist pub_obj;
void move(){    
  pub_obj.linear.x=1.0;
  pub_obj.linear.y=0.0;
  pub_obj.linear.z=0.0;
  pub_obj.angular.x=0.0;
  pub_obj.angular.y=0.0;
  pub_obj.angular.z=0.0;
  chatter_pub.publish(pub_obj);
}
void stop_moving()
{   
  pub_obj.linear.x=0.0;
  pub_obj.linear.y=0.0;
  pub_obj.linear.z=0.0;
  pub_obj.angular.x=0.0;
  pub_obj.angular.y=0.0;
  pub_obj.angular.z=0.5;
  chatter_pub.publish(pub_obj);
}
void laserCallback(const sensor_msgs::LaserScan::ConstPtr& array){
int i=0;

for (int i=0; i<720; i++){
    new_array[i]= array->ranges[i];
    //printf("%f",new_array[i]);
    if(new_array[i]<number)
    {
        //printf("%f", new_array[i]);
        void stop_moving();
        //pub_obj.linear.x=0.0;
        //pub_obj.angular.z=0.5;
        //chatter_pub.publish(pub_obj);
    }
    else
    {   void move();
        //pub_obj.linear.x=1.0;
        //chatter_pub.publish(pub_obj);
    }
}
}
int main(int argc, char** argv){
ros::init(argc,argv,"scan_sub_node");
ros::NodeHandle nh;
ros::Rate r(10);
chatter_pub = nh.advertise<geometry_msgs::Twist>("/car_diff_drive_controller/cmd_vel", 1);
ros::Subscriber sub_laser = nh.subscribe("/scan", 1000 , laserCallback);
//ros::Timer timer1=nh.createTimer(ros::Duration(5.0), msgCallback); //1 Hz
while(ros::ok()){
    ros::spinOnce();
    r.sleep();
}
return 0;
};