publish and subscribe in the same node but fails, subscribe does't work.

edit

In my opinion @jayess gave you the correct answer. I will just elaborate his comment more in details.

Subscribing to a topic requires a short amount of time, say 1 second. In your case, right after the first subscription, you enter the loop when the initialization is probably not complete yet. If this is the case, the number of publishers np will be 0. You thus subscribe again, sleep for 0.1 seconds and repeat. However, since you just re-subscribed, you can likely expect that the connection with the topic will not have been accomplished (again, it might take around 1s). You should easily see that this leads you to a loop in which the subscriber never has the time to fully connect with other nodes, since you re-initialize it every 0.1s. Note that the publisher-subscriber policy is fine with that: in general, a subscriber can expect any number of publishers, even zero, and since this is perfectly fine the roscpp client does not try to ensure that at least one publisher is found before leaving the initialization of a subscriber. You can simply drop your check: you will simply loose a couple of messages in the beginning, but eventually everything will work just fine.

If for any reason you must make sure that a subscriber has at least one publisher before entering the main loop, a better solution is to add, between the first ros::Subscriber sub = n.subscribe("chatter1", 1000, chatterCallback1); and the main loop, something like:

while(ros::ok() && sub.getNumPublishers() == 0)
  ros::Duration(0.2).sleep();

The ros::ok() condition is important in case you send a shutdown signal to the node while it is in this "initialization loop".

EDIT

Given your comment, try to compile and run the following code:

#include <ros/ros.h>
#include <std_msgs/String.h>

void callback(const std_msgs::String& msg) {
  ROS_INFO("I heard '%s'", msg.data.c_str());
}

int main(int argc, char** argv) {
  ros::init(argc, argv, "wait_for_publishers");
  ros::NodeHandle nh;

  ros::Subscriber sub = nh.subscribe("chatter", 1, callback);
  ros::Publisher pub = nh.advertise<std_msgs::String>("talk", 1);
  std_msgs::String msg;
  msg.data = "Hello";

  while(ros::ok() && sub.getNumPublishers() == 0) {
    ros::Duration(0.2).sleep();
    ROS_INFO_THROTTLE(1.0, "Waiting for publishers...");
  }

  ROS_INFO("There are now %d subscribers connected!", sub.getNumPublishers());

  ros::Rate rate(1);
  while(ros::ok()) {
    ros::spinOnce();
    pub.publish(msg);
    rate.sleep();
  }

  return 0;
}

It is a shorter version of your code, and when you start it you should see on the console the message "waiting for publishers" printed every second. In a new terminal, type:

rostopic pub -r 0.2 /chatter  std_msgs/String "data: 'ROS'"

You should now see (in node's terminal) that the program advanced by reporting 1 publisher and by printing every 5s the received message. In addition, it will publish every second a message in the topic talker. This runs fine in my PC, can you tell me if it is the same for you?