Undefined reference error while constructing a list of nodes

edit

Hello everyone I need to construct a list of odometric and laser measurement. For this purpose, I first wrote a .h file:

#include "ros/ros.h"
#include "nav_msgs/Odometry.h"
#include "geometry_msgs/Pose.h"
#include "geometry_msgs/Point.h"
#include "stdio.h"
#include "sensor_msgs/LaserScan.h"


class odom_node{
public:
    odom_node();
    ~odom_node();
    float xCoord;
    float yCoord;
    float angle;
    std::string frame_id;
    odom_node *next;
};

class scan_node{
public:
    scan_node();
    float scan[];
    std::string frame_id;
    scan_node *next;
};

class stage_listener{
public:
    stage_listener();

private:
    odom_node odom_graph;
    scan_node scan_list;
    void addOdomNode (const nav_msgs::Odometry);
};  

Then, in an associated .cpp file, I started defining the body of class stage_listener:

#include "ros/ros.h"
#include "nav_msgs/Odometry.h"
#include "geometry_msgs/Pose.h"
#include "geometry_msgs/Point.h"
#include "stdio.h"
#include "sensor_msgs/LaserScan.h"
#include "stage_listener.h"
#include "tf/transform_listener.h"

void addOdomNode (const nav_msgs::Odometry mes){
    geometry_msgs::Pose robot_pose = mes.pose.pose;
    geometry_msgs::Point robot_point = robot_pose.position;

    //float xCoord = robot_point.x;
    //float yCoord = robot_point.y;
    //float zCoord = robot_point.z;

    odom_node on;
    //on.xCoord = robot_point.x;
    //double orientation = tf::getYaw(robot_pose.orientation);
}

int main(){}

Anyway, for what regads line

odom_node on;

I get the following error, after digiting make, once inside my ros package:

CMakeFiles/stage_listener.dir/src/stage_listener.o: In function `addOdomNode(nav_msgs::Odometry_<std::allocator<void> >)':
/home/ubisum/fuerte_workspace/beginner/src/stage_listener.cpp:18: undefined reference to `odom_node::odom_node()'
/home/ubisum/fuerte_workspace/beginner/src/stage_listener.cpp:18: undefined reference to `odom_node::~odom_node()'

Does anyone know the reason? I'm sorry if question may seem too silly, but I'm learning C++ and ROS at the once and it's not easy when coming from Java and MatLab.

Thanks for help