having problems with subscribe when using boost::bind

edit

here is my code

#include <ros/ros.h>
#include "costmap/costmap.h"
#include <sensor_msgs/LaserScan.h>
int main(int argc, char **argv) {
    ros::init(argc, argv, "costmap");
    ros::NodeHandle n;
    costmap costmap_;
    ros::Subscriber sub = n.subscribe<sensor_msgs::LaserScan::ConstPtr>("scan", 1000, boost::bind(&upDateMap, _1, costmap_));
    ros::spin();
    return 0;}

void upDateMap(const sensor_msgs::LaserScan::ConstPtr &msg, costmap &costmap_){}

and here is my costmap.h:

void upDateMap(const sensor_msgs::LaserScan::ConstPtr &msg, costmap &costmap_);
class costmap {};

costmap is a class defined by me.

When i run catkin_make,In file included from /home/mushen/catkin_ws/src/costmap/src/costmap.cpp:1:0: /home/mushen/catkin_ws/src/costmap/include/costmap/costmap.h:14:61: error: ‘costmap’ has not been declared comes out.

how could i solve this?