ROS：：计算时间间隔

ros中计算时间间隔

  double before_time_//是一个全局变量

  //其他代码
     ...
     ...
     
  double now = ros::Time::now().toSec();
  std::cout << "time:" << (now - before_time_)*1000 << std::endl;
  before_time_ = now;