ros service crash with no message [closed]

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i wanna use a serve to subscribe the "/scan" topic and in the other node i creat a client to request the lasersan data from the serve.But it sometimes crashes when running and no meessage showed in the terminal,in fact the two nodes are just exit directly.i donot know why ,here is the code ,thanks for looking and helping me slove it:

-----------------server

#include <vector>
#include "ros/ros.h"
 #include <boost/thread/mutex.hpp>
#include "vfh_to_goal/get_Laser.h"
#include "sensor_msgs/LaserScan.h" 
  boost::mutex scan_mutex_;
sensor_msgs::LaserScan scan;
bool flag = false;
void scanCallback(const sensor_msgs::LaserScan::ConstPtr &scan1)
{
    scan = *scan1;
    flag = true;
    ROS_INFO("get laser");
}
bool getLaser(vfh_to_goal::get_Laser::Request &req,
                           vfh_to_goal::get_Laser::Response &res  )
{
      if(req.get && flag)
      {
         scan_mutex_.lock();
            res.scan = scan;
            ROS_INFO("copy laser to srv");
            flag = false;
        scan_mutex_.unlock();
      }
        return true;
}

-------client

bool getlaser()
{
    int num_laser=0;
       ros::Rate loop_rate(20);
    while(num_laser==0)
    {
        cout<<"0"<<num_laser<<endl;
        vfh_to_goal::get_Laser srv1;
        srv1.request.get=true;
        if(client_srv.call(srv1))
        {
            num_laser=srv1.response.scan.ranges.size() ;
             cout<<"1：："<<num_laser<<endl;
            if(num_laser==0)
                continue;
            else
            {
                 cout<<"2"<<endl;
                laserdata.clear();
                vector<float>::reverse_iterator it=srv1.response.scan.ranges.rbegin();
                while(it!=srv1.response.scan.ranges.rend())
                {
                    laserdata.push_back(*it);
                    ++it;
                }
                explore_value=(double)srv1.response.scan.range_max-0.1;
                break;
            }
        }
        else
        {
                cout<<"laser_serve can not connect!"<<endl;
        }
        loop_rate.sleep();
    }

    return true;
}

int main(int argc, char** argv)
{
    ros::init(argc, argv, "get_laser_serv");
    ros::NodeHandle n;
    ros::ServiceServer service = n.advertiseService("get_laser_gy", getLaser);
    ros::Subscriber sub = n.subscribe<sensor_msgs::LaserScan>("/scan", 50, &scanCallback);
    ros::spin();
}