void handler(
         const boost::system::error_code& error,
         int signal_number)
{
  if (!error)
    {
      static bool first = true;
      if(first){
        std::cout << " A signal(SIGINT) occurred." << std::endl;
        // do something like writing data to a file
        first = false;
      }else{
        std::cout << " A signal(SIGINT) occurred, exiting...." << std::endl;
        exit(0);
      }
    }
}

int main(){
  // Construct a signal set registered for process termination.
  boost::asio::io_service io;
  boost::asio::signal_set signals(io, SIGINT);
  // Start an asynchronous wait for one of the signals to occur.
  signals.async_wait(handler);
  io.run();
  size_t i;
  for(i=0;i<std::numeric_limits<size_t>::max();++i){
    // time stepping loop, do some computations
  }
  std::cout << i << std::endl;
  return 0;
}