Problem with subscribing to a topic that contains slash

edit

I noticed something weird that seems like a bug. When a subscriber listens to a topic that contains a slash and that a publisher advertises the "parent" topic (the part before the slash), then the subscriber changes the topic to what it listens to match the publisher.

Here is an example. I open three terminals that will exchange on topic /parent/child.

Step 1: In Terminal 1, I start rostopic echo /parent/child

Step 2: In Terminal 2, I start rostopic echo /parent

Step 3: In Terminal 3, I start a node with publishers for /parent and parent/child

Step 4: In Terminal 3, the node publishes on both topics

The result is that only the subscriber in Terminal 2 gets the message. In addition, rxgraph shows that Terminal 1 is then subscribing to /parent instead of /parent/child. In Terminal 1, I get this instead of the message: no field named [/child]

What's happening here?

Here is the code:

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

int main(int argc, char** argv)
{  
    ros::init(argc, argv, "MyPublisher");

    ros::NodeHandle nh("~");

    ros::Rate oneSecond(1);

    // Creates a publisher to see if it replicates the bug
    ros::Publisher pubParent = nh.advertise<std_msgs::String>("/parent", 10);

    // Waits for the subscribers to connect
    oneSecond.sleep();

    ros::Publisher pubChild = nh.advertise<std_msgs::String>("/parent/child", 10);

    // Waits for the subscribers to connect
    oneSecond.sleep();


    std_msgs::String msgChild;
    msgChild.data = "Hello World! (on /parent/child)";
    pubChild.publish(msgChild);
    ROS_INFO("Message published (on /parent/child)");


    std_msgs::String msgParent;
    msgParent.data = "Hello World! (on /parent)";
    pubParent.publish(msgParent);
    ROS_INFO("Message published (on /parent)");

    // Waits for the user to manually stop the node (to give time to see the update in rxgraph)
    ros::spin();

    return 0;
}

Here is the info about the nodes:

Terminal 1:

Node [/rostopic_27422_1352897219007]
Publications: 
 * /rosout [rosgraph_msgs/Log]

Subscriptions: 
 * /parent [std_msgs/String]

Services: None
Pid: 27422
Connections:
 * topic: /rosout
    * to: /rosout
    * direction: outbound
    * transport: TCPROS
 * topic: /parent
    * to: /MyPublisher (http://dfki-benoit:33822/)
    * direction: inbound
    * transport: TCPROS

Terminal 2:

Node [/rostopic_27405_1352897218194]
Publications: 
 * /rosout [rosgraph_msgs/Log]

Subscriptions: 
 * /parent [std_msgs/String]

Services: None
Pid: 27405
Connections:
 * topic: /rosout
    * to: /rosout
    * direction: outbound
    * transport: TCPROS
 * topic: /parent
    * to: /MyPublisher (http://dfki-benoit:33822/)
    * direction: inbound
    * transport: TCPROS

Terminal 3:

Node [/MyPublisher]
Publications: 
 * /parent [std_msgs/String]
 * /parent/child [std_msgs/String]
 * /rosout [rosgraph_msgs/Log]

Subscriptions: None

Services: 
 * /MyPublisher/get_loggers
 * /MyPublisher/set_logger_level
Pid: 27455
Connections:
 * topic: /rosout
    * to: /rosout
    * direction: outbound
    * transport: TCPROS
 * topic: /parent
    * to: /rostopic_27405_1352897218194
    * direction: outbound
    * transport: TCPROS
 * topic: /parent
    * to: /rostopic_27422_1352897219007
    * direction: outbound
    * transport: TCPROS

EDIT (12/12/12): Following the answer from @Dirk Thomas, I tried his Python script. The behavior that I observe is the following. If I start the standard Python listener and rostopic echo, they both receive the messages on /parent/child. However, if I start only rostopic echo, then it "switches" to /parent and tries to read the field /child. In addition, rostopic echo does not print the WARNING: topic [/parent/child] does not appear to be published yet if the standard ... (more)