impossible to register messages in a bag file

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Hi all,
I wrote a c++ script to send messages to a certain topic:

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

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

    ros::Publisher chatter_pub = n.advertise<std_msgs::string>("/end",1000);
    ros::Rate loop_rate(10);

    std_msgs::String msg;
    msg.data = "end of loop";
    chatter_pub.publish(msg);

    //ROS_INFO("Message sent: %s",msg.data.c_str());
    while(chatter_pub.getNumSubscribers()==0){
        ros::spinOnce();
    }
    //sleep(10);
    loop_rate.sleep();
    ROS_INFO("Message sent: %s",msg.data.c_str());
    return 0;
}

From a shell, I started recording messages sent to topic /end :

rosbag record -O end /end 

After sending of the messages, I analyzed bag file and I didn't find anything inside it. Do you have any idea why this happens? I tried also to substitute the while in the code with while(1) but no messages is received as well.

Thanks for support.