前段時間，寫了一點關于智能指針的東西，有讀者反映沒有代碼比較難懂．現給出源碼，并稍微加以解釋.
智能指針類用到的基類的定義:
template<typename T>
class HandleBase
{
public:
typedef T element_type;
T* get() const
{
return _ptr;
}
//重載->操作符，返回所指對象的指針.
T* operator->() const
{
if(!_ptr)
{
//
// We don't throw directly NullHandleException here to
// keep the code size of this method to a minimun (the
// assembly code for throwing an exception is much bigger
// than just a function call). This maximises the chances
// of inlining by compiler optimization.
//
throwNullHandleException(__FILE__, __LINE__);
}
return _ptr;
}
// 通過智能指針獲取所指對象的引用.
T& operator*() const
{
if(!_ptr)
{
//
// We don't throw directly NullHandleException here to
// keep the code size of this method to a minimun (the
// assembly code for throwing an exception is much bigger
// than just a function call). This maximises the chances
// of inlining by compiler optimization.
//
throwNullHandleException(__FILE__, __LINE__);
}
return *_ptr;
}
operator bool() const
{
return _ptr ? true : false;
}
void swap(HandleBase& other)
{
std::swap(_ptr, other._ptr);
}
T* _ptr;
private:
void throwNullHandleException(const char *, int) const;
};
......
// 智能指針類定義
template<typename T>
class Handle : public HandleBase<T>
{
public:
Handle(T* p = 0) //智能指針的構造函數
{
this->_ptr = p;
if(this->_ptr)
{
this->_ptr->__incRef(); //在構造函數中增加所指對象的引用計數
}
}
template<typename Y> //拷貝構造函數
Handle(const Handle<Y>& r)
{
this->_ptr = r._ptr;
if(this->_ptr)
{
this->_ptr->__incRef(); //在構造函數中增加所指對象的引用計數
}
}
Handle(const Handle& r) //拷貝構造函數
{
this->_ptr = r._ptr;
if(this->_ptr)
{
this->_ptr->__incRef(); //在構造函數中增加所指對象的引用計數
}
}
~Handle()
{
if(this->_ptr)
{
this->_ptr->__decRef(); //在析構函數中減少所指對象的引用計數
}
}
// 重載=操作符, 要注意所有權 (即，對原實例的處理).
Handle& operator=(T* p)
{
if(this->_ptr != p)
{
if(p)
{
p->__incRef(); //增加新指對象的引用計數
}
T* ptr = this->_ptr;
this->_ptr = p;
if(ptr)
{
ptr->__decRef(); //減少原來所指對象的引用計數
}
}
return *this;
}
template<typename Y>
Handle& operator=(const Handle<Y>& r)
{
if(this->_ptr != r._ptr)
{
if(r._ptr)
{
r._ptr->__incRef(); //增加新指對象的引用計數
}
T* ptr = this->_ptr;
this->_ptr = r._ptr;
if(ptr)
{
ptr->__decRef(); //減少原來所指對象的引用計數
}
}
return *this;
}
Handle& operator=(const Handle& r)
{
if(this->_ptr != r._ptr)
{
if(r._ptr)
{
r._ptr->__incRef(); //增加新指對象的引用計數
}
T* ptr = this->_ptr;
this->_ptr = r._ptr;
if(ptr)
{
ptr->__decRef(); //減少原來所指對象的引用計數
}
}
return *this;
}
跟智能指針配合使用的對象．要能夠跟指針智能配合使用，這些對象應該是從下列類的派生類的實例．
class SimpleShared
{
public:
SimpleShared();
SimpleShared(const SimpleShared&);
virtual ~SimpleShared()
{
}
SimpleShared& operator=(const SimpleShared&)
{
return *this;
}
void __incRef()
{
assert(_ref >= 0);
++_ref;
}
void __decRef()
{
assert(_ref > 0);
if(--_ref == 0) // 如果引用計數為0,則摧毀對象本身．
{
if(!_noDelete)
{
_noDelete = true;
delete this;
}
}
}
int __getRef() const
{
return _ref;
}
void __setNoDelete(bool b)
{
_noDelete = b;
}
private:
int _ref;
bool _noDelete;
};
class Shared
{
public:
Shared();
Shared(const Shared&);
virtual ~Shared()
{
}
Shared& operator=(const Shared&)
{
return *this;
}
virtual void __incRef();
virtual void __decRef();
virtual int __getRef() const;
virtual void __setNoDelete(bool);
protected:
#if defined(_WIN32)
LONG _ref;
#elif defined(ICE_HAS_ATOMIC_FUNCTIONS)
volatile int _ref;
#else
int _ref;
Mutex _mutex;
#endif
bool _noDelete;
};