getNamespace returns double slash

edit

Hello everybody, I am experiencing a weird error. Considering a launch file where I launch a node in either of the two following ways

<node name="velocity_control" pkg="uav_velocity_control" type="ControlNode"  ns="vtol" output="screen"/>

or

  <group ns="vtol">
    <node name="velocity_control" pkg="uav_velocity_control" type="ControlNode"  output="screen"/>   
  </group>

In my node I have the following line of code

ros::Subscriber sub = n.subscribe(ros::this_node::getNamespace() + "/attitude", queue_size, callbackAngularVelocities);

However if I print the obtained topic name

std::cout << ros::this_node::getNamespace() << "/attitude" << std::endl;

I obtain

//vtol/attitude

I cannot understand this behaviour. I temporarily solved hardcoding the namespace in the node, but I believe you understand the importance of setting the namespaces in the launch file.

Thank you very much

Andrea