Why "subs_.push_back" in listener_with_userdata.cpp

[weiweikong]

1. What is the meaing for push_back() here and why we use vector to manage the construction of the three different chatterCallback?
2. Why can not use the bellowing codes

void init()
  {
    node_handle_.subscribe<std_msgs::String>("chatter", 1000, boost::bind(&Listener::chatterCallback, this, _1, "User 1"));
    node_handle_.subscribe<std_msgs::String>("chatter", 1000, boost::bind(&Listener::chatterCallback, this, _1, "User 2"));
    node_handle_.subscribe<std_msgs::String>("chatter", 1000, boost::bind(&Listener::chatterCallback, this, _1, "User 3"));
  }

to initialse the different callback function?

[dirk-thomas]

The subscribe function returns a reference counted subscriber. When all copies of it go out of scope it will unsubscribe from the topic. Therefore the subscribers are stored in a vector to prevent them from going out of scope.

Please read the documentation of the function (NodeHandle::subscribe: http://docs.ros.org/indigo/api/roscpp/html/classros_1_1NodeHandle.html#a317fe4c05919e0bf3fb5162ccb2f7c28) and ask future questions on answers.ros.org.

[weiweikong]

@dirk-thomas thanks for your kind reply. There are still some confusions. More details please refer to http://answers.ros.org/question/234538/why-subs_push_back-in-listener_with_userdatacpp .