NS-3 中 Callback与MakeCallback的简单说明

Callback 与  MakeCallback是成对出现的。

1. Callback
http://www.nsnam.org/doxygen/classns3_1_1_callback.html
个人理解： Callback其实类似于“指向函数的指针"

Callback模板类： Callback< R, T1, T2, T3, T4, T5, T6, T7, T8, T9 >
其中 R为Callback的返回类型，必选
T1...T9是Callback的实参，可选，默认值为empty


2. MakeCallback
http://www.nsnam.org/doxygen/group___make_callback.html

template<typename T , typename OBJ , typename R , typename T1 >
Callback< R, T1 > ns3::MakeCallback (R(T::*)(T1)      mem_ptr,    OBJ      objPtr)     
模板类MakeCallback的返回值为Callback类型

mem_ptr: class method member pointer
objPtr:  class instance
返回值： a wrapper Callback Build Callbacks for class method members which takes one argument and potentially return a value.

3. 一个简单的例子：
 
 
   typedef Callback<void, Ptr<Vehicle>, std::string, Ptr<const Packet> > DeviceTraceCallback;    //在类外定义
   
private:
   DeviceTraceCallback m_devTxTrace;
   
public:
   DeviceTraceCallback GetDevTxTraceCallback() {return m_devTxTrace;}
   void SetDevTxTraceCallback(DeviceTraceCallback devTxTrace) {  m_devTxTrace = devTxTrace; }
   
protected:
   void DevTxTrace (std::string context, Ptr<const Packet> p) { m_devTxTrace(Ptr<Vehicle>(this), context, p);}
   
实现：
   std::ostringstream oss;
   oss << "/NodeList/" << m_node->GetId()<< "/DeviceList/0/Mac/MacTx";
    Config::Connect (oss.str(), MakeCallback (&Vehicle::DevTxTrace, this));