**
创建一个节点,同时实现订阅与发布
==以turtlesim为例,创建一个发布topic控制海龟圆周运动==
==同时订阅海龟/turtle1/pose话题,终端打印pose信息==
==再新建一个/vel_info话题,发布速度信息==
==新建一个订阅者,订阅刚刚发布的速度信息==
都在同一个节点里实现
#include "ros/ros.h"
#include <iostream>
#include "std_msgs/String.h"
#include "geometry_msgs/Twist.h"
#include <turtlesim/Pose.h>
#include <ros/console.h>
using namespace std;
void turtle1posecallback(const turtlesim::Pose& pose)
{
bool FLAG;
int x = (int) pose.x;
int y = (int) pose.y;
if(x > 0