ROS中节点在每次接收到消息之后都发布一条消息的反馈topic

#include "ros/ros.h"
#include "std_msgs/String.h"
#include <sstream>
ros::Publisher chatter_pub;
ros::Subscriber sub;
void callback()
{
std_msgs::String msg;

std::stringstream ss;
msg.data = "test";

ROS_INFO("%s", msg.data.c_str());

chatter_pub.publish(msg);
}
void function(const std_msgs::StringPtr &msg)
{
callback();
}

int main(int argc, char **argv)
{

ros::init(argc, argv, "talker");

ros::NodeHandle n;

chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
sub = n.subscribe("/test", 1, &function);

ros::Rate loop_rate(10);

ROS_INFO("Please send message!");

ros::spin();

return 0;
}

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

#include <sstream>

int main(int argc, char **argv)
{

ros::init(argc, argv, "talker");

ros::NodeHandle n;

ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);

ros::Rate loop_rate(10);

int count = 0;

while (count < 1)
{

std_msgs::String msg;

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

ROS_INFO("%s", msg.data.c_str());
if(chatter_pub.getNumSubscribers() == 1)
{
chatter_pub.publish(msg);

count ++;

ros::spinOnce();

loop_rate.sleep();
++count;
}
}

return 0;
}