#include "ros/ros.h"
#include <signal.h>
 
void MySigintHandler(int sig)
{
    //這里主要進行退出前的數(shù)據(jù)保存、內(nèi)存清理、告知其他節(jié)點等工作
    ROS_INFO("shutting down!");
    ros::shutdown();
}
 
int main(int argc, char** argv){
//ros::init()
    /**
      * The ros::init() function needs to see argc and argv so that it can perform
      * any ROS arguments and name remapping that were provided at the command line. For programmatic
      * remappings you can use a different version of init() which takes remappings
      * directly, but for most command-line programs, passing argc and argv is the easiest
      * way to do it.  The third argument to init() is the name of the node.
      *
      * You must call one of the versions of ros::init() before using any other
      * part of the ROS system.
    */
    ros::init(argc, argv, "ist_node");
    //初始化節(jié)點名字必須在最前面，如果ROS系統(tǒng)中出現(xiàn)重名，則之前的節(jié)點會被自動關閉
    //如果想要多個重名節(jié)點而不報錯，可以在init中添加ros::init_options::AnonymousName參數(shù)
    //該參數(shù)會在原有節(jié)點名字的后面添加一些隨機數(shù)來使每個節(jié)點獨一無二
    //ros::init(argc, argv, "my_node_name", ros::init_options::AnonymousName);
 
//ros::NodeHandle
    /**
      * NodeHandle is the main access point to communications with the ROS system.
      * The first NodeHandle constructed will fully initialize this node, and the last
      * NodeHandle destructed will call ros::shutdown() to close down the node.
    */
    ros::NodeHandle h_node;
    //獲取節(jié)點的句柄,init是初始化節(jié)點，這個是Starting the node
    //如果不想通過對象的生命周期來管理節(jié)點的開始和結(jié)束，你可以通過ros::start()和ros::shutdown() 來自己管理節(jié)點。
    
    ros::Rate loop_rate(1);
    //loop once per second
    //Cannot use before the first NodeHandle has been created or ros::start() has been called.
 
//shut down
    signal(SIGINT, MySigintHandler);
    //覆蓋原來的Ctrl+C中斷函數(shù)，原來的只會調(diào)用ros::shutdown()
    //為你關閉節(jié)點相關的subscriptions, publications, service calls, and service servers，退出進程
 
//run status
    int sec = 0;
    while(ros::ok() && sec++ < 5){
        loop_rate.sleep();
        ROS_INFO("ROS is ok!");
        ros::spinOnce();
    }
    //ros::ok()返回false，代表可能發(fā)生了以下事件
        //1.SIGINT被觸發(fā)(Ctrl-C)調(diào)用了ros::shutdown()
        //2.被另一同名節(jié)點踢出 ROS 網(wǎng)絡
        //3.ros::shutdown()被程序的另一部分調(diào)用
        //4.節(jié)點中的所有ros::NodeHandles 都已經(jīng)被銷毀
    //ros::isShuttingDown():一旦ros::shutdown()被調(diào)用（注意是剛開始調(diào)用，而不是調(diào)用完畢），就返回true
    //一般建議用ros::ok()，特殊情況可以用ros::isShuttingDown()
 
    ROS_INFO("Node exit");
    printf("Process exit\n");
    return 0;
}