首先明确下三个类的作用：

There are three special base classes used in ns-3. Classes that inherit from these base classes can instantiate objects with special properties. These base classes are:

  • class Object
  • class ObjectBase
  • class SimpleRefCount

It is not required that ns-3 objects inherit from these class, but those that do get special properties. Classes deriving from class Object get the following properties.

  • the ns-3 type and attribute system (see Configuration and Attributes)
  • an object aggregation system
  • a smart-pointer reference counting system (class Ptr)

Classes that derive from class ObjectBase get the first two properties above, but do not get smart pointers. Classes that derive from class SimpleRefCount: get only the smart-pointer reference counting system.

In practice, class Object is the variant of the three above that the ns-3 developer will most commonly encounter.

从官方文档中的这段叙述中，我们可以看出来，Object类的功能是类ObjectBase功能和SimpleRefCount的并集，后两者对前者的功能构成一个划分。

从代码中我们可以容易看出，Object类对SimpleRefCount有继承关系，而ObjectBase类独自实现，与前两者没有关系。

SimpleRefCount

NS3中由于SimpleRefCount类过于Simple，所以源文件和接口文件放在了同一个文件里。也就是文件simple-ref-count.h文件，在core目录下。

SimpleRefCount保有一个私有变量用来记录引用的数量，并通过两个函数Ref和Unref来对这个变量进行自增和自减操作，当判断为0时，执行内存的释放。

这两个函数不需要用户手动执行，而是通过智能指针Ptr来调用的。

ObjectBase

NS3中的ObjectBase类可以看作一个简化版的Object类，这个类主要的函数有：

SetAttribute

void SetAttribute (std::string name, const AttributeValue &value);

用来根据名称设置值，比如：

txQueue->SetAttribute ("MaxSize", StringValue ("60p"));

这条语句将名字MaxSize所绑定的变量的值设置为StringValue ("60p")。

TraceConnect

bool TraceConnect (std::string name, std::string context, const CallbackBase &cb);

这个函数用来在连接在tid中添加的对于类中某一变量的Trace，这个函数主要负责当Trace的值更好后通知回调函数cb。

Object

NS3中的object类继承了类SimpleRefCount<Object, ObjectBase, ObjectDeleter>。由于这个类继承了类ObjectBase，所以ObjectBase类中的成员函数类Object也有。除此之外，这个类中主要的函数有：

GetObject

template <typename T> inline Ptr<T> GetObject (void) const;

这个函数主要用来得到一个绑定的某类型的实例，比如：

Ptr<Ipv4> ipv4 = node->GetObject<Ipv4> ();

是把node中的Ipv4类型提取出来。

AggregateObject

  /**
   * Aggregate two Objects together.
   *
   * \param [in] other The other Object pointer
   *
   * This method aggregates the two Objects together: after this
   * method returns, it becomes possible to call GetObject()
   * on one to get the other, and vice-versa. 
   *
   * This method calls the virtual method NotifyNewAggregates() to
   * notify all aggregated Objects that they have been aggregated
   * together.
   *
   * \sa NotifyNewAggregate()
   */
  void AggregateObject (Ptr<Object> other);

参考文献