how to use tf listener

edit

it didn't fit in comment space,so i'm writing here.. I try to give an example,what I'm doing is:

#include <ros/ros.h>
#include <tf/tf.h>
#include <tf/transform_listener.h>
"others include..."

tf::TransformListener listener; //as global variable
ros::Publisher pubLaser;
"others global variables..."

void findCoords(const sensor_msgs::LaserScanPtr dataFromLaser){
   //in this function I have to transform,so i do the stuff and then..
   listener.transformPoint("base_link",point,newPoint);
   //where point,newPoint are StampedPoint
}

void laserCallback(const sensor_msgs::LaserScan::ConstPtr& fromLaser){
   //do stuff...
   findCoords(data);
}

int main(int argc,char** argv){
   ros::init(argc,argv,"name");
   ros::NodeHandle nh;
   ros::Subscriber laser=nh.subscribe("base_scan",10,laserCallback);
   pubLaser=nh.advertise<sensor_msgs::LaserScan>("from_Laser",100);
   ros::spin();
   return 0;
}

If i run it without the part of tf it works,but i didn't figure out how to make it run with tf,it gives me the error i said in the first post.