ROS学习笔记(一)：一个简单的ros程序有哪些必不可少的元素

#include "ros/ros.h"
#include "std_msgs/String.h"

#include <sstream>
int main(int argc, char **argv)
{
  /**
   * 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, "talker");
  //在建立ros的第一个节点时一定要先调用初始化节点ros::init()
  //节点名称要唯一


  /**
   * 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 close down the node.
   */
  ros::NodeHandle n;
  //NodeHandle指定命名空间，n的命名空间是talker
  //ros::NodeHandle n("my_namespace")命名空间是talker/my_namespace

  /**
   * The advertise() function is how you tell ROS that you want to
   * publish on a given topic name. This invokes a call to the ROS
   * master node, which keeps a registry of who is publishing and who
   * is subscribing. After this advertise() call is made, the master
   * node will notify anyone who is trying to subscribe to this topic name,
   * and they will in turn negotiate a peer-to-peer connection with this
   * node.  advertise() returns a Publisher object which allows you to
   * publish messages on that topic through a call to publish().  Once
   * all copies of the returned Publisher object are destroyed, the topic
   * will be automatically unadvertised.
   *
   * The second parameter to advertise() is the size of the message queue
   * used for publishing messages.  If messages are published more quickly
   * than we can send them, the number here specifies how many messages to
   * buffer up before throwing some away.
   */
  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
  //advertise()函数用来发布一个消息类型为std_msgs/String名字叫chatter的话题
  //参数1000表示推送消息队列大小，防止消息推送的速度太快

  ros::Rate loop_rate(10);
  //定义一个循环的频率，这里是指定发布消息的频率为10Hz，每秒十次

  /**
   * A count of how many messages we have sent. This is used to create
   * a unique string for each message.
   */
  int count = 0;
  //count 记录发布消息的总次数
  while (ros::ok())
  {
    /**
     * This is a message object. You stuff it with data, and then publish it.
     */
    std_msgs::String msg;

    std::stringstream ss;
    ss << "hello world " << count;
    msg.data = ss.str();

    ROS_INFO("%s", msg.data.c_str());
    //ros::ok() 返回false的几种情况，即循环结束：
    //SIGINT收到(Ctrl-C)信号
    //另一个同名节点启动，会先中止之前的同名节点
    //ros::shutdown()被调用
    //所有的ros::NodeHandles被销毁

    //定义字符串流“hello world”并赋值给ss, 转为字符串类型的消息
    //ROS_INFO()输出信息，相当于cout

    /**
     * The publish() function is how you send messages. The parameter
     * is the message object. The type of this object must agree with the type
     * given as a template parameter to the advertise<>() call, as was done
     * in the constructor above.
     */
    chatter_pub.publish(msg);
    //发布消息

    ros::spinOnce();
    //程序中有订阅功能时必须加上这个函数，没有的话可以不加，一般都会加上

    loop_rate.sleep();
    //控制循环的频率

    ++count;
  }

  return 0;
}