訂閱節點，主要經過subscribe方式。html
最多見的使用方法api
void callback(const std_msgs::Empty::ConstPtr& message) { } ros::Subscriber sub = handle.subscribe("my_topic", 1, callback);
其中subscribe有不少重定義。例如：函數
Subscriber ros::NodeHandle::subscribe ( const std::string & topic, uint32_t queue_size, void(*)(M) fp, const TransportHints & transport_hints = TransportHints() )
Parameters:ui
| M | [template] M here is the callback parameter type (e.g. const boost::shared_ptr<M const>& or const M&), not the message type, and should almost always be deduced |
| topic | Topic to subscribe to |
| queue_size | Number of incoming messages to queue up for processing (messages in excess of this queue capacity will be discarded). |
| fp | Function pointer to call when a message has arrived |
| transport_hints | a TransportHints structure which defines various transport-related options |
其中的參數： this
topic 爲訂閱的節點名，字符串類型。spa
queue_size 爲待處理信息隊列大小。ssr
fp 當消息傳入時，能夠調用的函數指針，即回調函數。指針
而其中M是回調函數的不一樣類型，例如const boost::shared_ptr<M const>& or const M&。這樣的話，咱們還能夠使用boost::bind()調用回調函數。code
可是，咱們還會遇到subscribe()的第四個參數，例如：htm
Subscriber ros::NodeHandle::subscribe ( const std::string & topic, uint32_t queue_size, void(T::*)(M) fp, T * obj, const TransportHints & transport_hints = TransportHints() )
Parameters:
| M | [template] M here is the message type |
| topic | Topic to subscribe to |
| queue_size | Number of incoming messages to queue up for processing (messages in excess of this queue capacity will be discarded). |
| fp | Member function pointer to call when a message has arrived |
| obj | Object to call fp on |
| transport_hints | a TransportHints structure which defines various transport-related options |
當咱們要使用一個Class裏面的返回函數以後，咱們須要調用第四個參數。例如咱們有一個class：
class Listener { public: void callback(const std_msgs::String::ConstPtr& msg); };
若是想要調用這個class裏的返回函數，能夠使用第四個參數，以下：
Listener listener; ros::Subscriber sub = n.subscribe("chatter", 1000, &Listener::callback, &listener);
第四個參數定義的class，這樣咱們調用的就是Listener的callback函數。若是方法在class裏面，能夠使用this。以下：
class Listener { public: void callback(const std_msgs::String::ConstPtr& msg){}
ros::Subscriber sub = n.subscribe("chatter", 1000, &Listener::callback, this);
void TestObject(ros::NodeHandle n)
{
}
};
這樣能夠調用Class裏的回調函數啦。
參考資料
ROS::NodeHandle ：
Using Class Methods as Callbacks：
http://wiki.ros.org/roscpp_tutorials/Tutorials/UsingClassMethodsAsCallbacks\
Using Class Methods as Callbacks issu：
https://answers.ros.org/question/207254/setting-class-method-callback-from-within-object-c/
第四個參數：