How to add new subscriber in move_base node ?

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Hello,

I have integrated listener.cpp subscriber (from ROS tutorials) into the move_base node. I started move_base node and after I started talker.cpp node. But it does not work. Following steps show my process, where I am doing wrong ?

in move_base.h

ros::Subscriber listen_;

void listenCallback(const std_msgs::String::ConstPtr& msg);

in move_base.cpp

ros::NodeHandle listen_nh_;

listen_=  listen_nh_.subscribe<std_msgs::String>("chatter", 1, boost::bind(&MoveBase::listenCallback, this, _1));

void MoveBase::listenCallback(const std_msgs::String::ConstPtr& msg) {

 ROS_INFO("I heard: [%s]", msg->data.c_str());

}

So this is what I do. Do have any idea what my failure is or something forgetting ?

thanks