看到ATL中有3個類的代碼比較比較重復，在atlbase.h中，分別是CAutoVectorPtr, CAutoPtr和CAutoStackPtr，他們的功能其實很類似STL中的autoptr, 但是這里因為針對不同的分配對象而用了3個不同的類，其中CAutoVectorPtr是針對數組類型的，CAutoPtr是針對普通的非數組類型，而CAutoStackPtr針對的是_malloca分配的類型，因為最后釋放方式的不同，它這里用了3份代碼來實現。
CAutoVectorPtr:
template< typename T >
class CAutoVectorPtr
{
public:
CAutoVectorPtr() throw() :
m_p( NULL )
{
}
CAutoVectorPtr( CAutoVectorPtr< T >& p ) throw()
{
m_p = p.Detach(); // Transfer ownership
}
explicit CAutoVectorPtr( T* p ) throw() :
m_p( p )
{
}
~CAutoVectorPtr() throw()
{
Free();
}
operator T*() const throw()
{
return( m_p );
}
CAutoVectorPtr< T >& operator=( CAutoVectorPtr< T >& p ) throw()
{
if(*this==p)
{
if(m_p == NULL)
{
// This branch means both two pointers are NULL, do nothing.
}
else if(this!=&p)
{
// If this assert fires, it means you attempted to assign one CAutoVectorPtr to another when they both contained
// a pointer to the same underlying vector. This means a bug in your code, since your vector will get
// double-deleted.
ATLASSERT(FALSE);
// For safety, we are going to detach the other CAutoVectorPtr to avoid a double-free. Your code still
// has a bug, though.
p.Detach();
}
else
{
// Alternatively, this branch means that you are assigning a CAutoVectorPtr to itself, which is
// pointless but permissible
// nothing to do
}
}
else
{
Free();
Attach( p.Detach() ); // Transfer ownership
}
return( *this );
}
// basic comparison operators
bool operator!=(CAutoVectorPtr<T>& p) const
{
return !operator==(p);
}
bool operator==(CAutoVectorPtr<T>& p) const
{
return m_p==p.m_p;
}
// Allocate the vector
bool Allocate( size_t nElements ) throw()
{
ATLASSUME( m_p == NULL );
ATLTRY( m_p = new T[nElements] );
if( m_p == NULL )
{
return( false );
}
return( true );
}
// Attach to an existing pointer (takes ownership)
void Attach( T* p ) throw()
{
ATLASSUME( m_p == NULL );
m_p = p;
}
// Detach the pointer (releases ownership)
T* Detach() throw()
{
T* p;
p = m_p;
m_p = NULL;
return( p );
}
// Delete the vector pointed to, and set the pointer to NULL
void Free() throw()
{
delete[] m_p;
m_p = NULL;
}
public:
T* m_p;
};
CAutoPtr：
template< typename T >
class CAutoPtr
{
public:
CAutoPtr() throw() :
m_p( NULL )
{
}
template< typename TSrc >
CAutoPtr( CAutoPtr< TSrc >& p ) throw()
{
m_p = p.Detach(); // Transfer ownership
}
CAutoPtr( CAutoPtr< T >& p ) throw()
{
m_p = p.Detach(); // Transfer ownership
}
explicit CAutoPtr( T* p ) throw() :
m_p( p )
{
}
~CAutoPtr() throw()
{
Free();
}
// Templated version to allow pBase = pDerived
template< typename TSrc >
CAutoPtr< T >& operator=( CAutoPtr< TSrc >& p ) throw()
{
if(m_p==p.m_p)
{
// This means that two CAutoPtrs of two different types had the same m_p in them
// which is never correct
ATLASSERT(FALSE);
}
else
{
Free();
Attach( p.Detach() ); // Transfer ownership
}
return( *this );
}
CAutoPtr< T >& operator=( CAutoPtr< T >& p ) throw()
{
if(*this==p)
{
if(this!=&p)
{
// If this assert fires, it means you attempted to assign one CAutoPtr to another when they both contained
// a pointer to the same underlying object. This means a bug in your code, since your object will get
// double-deleted.
#ifdef ATL_AUTOPTR_ASSIGNMENT_ASSERT
ATLASSERT(FALSE);
#endif
// For safety, we are going to detach the other CAutoPtr to avoid a double-free. Your code still
// has a bug, though.
p.Detach();
}
else
{
// Alternatively, this branch means that you are assigning a CAutoPtr to itself, which is
// pointless but permissible
// nothing to do
}
}
else
{
Free();
Attach( p.Detach() ); // Transfer ownership
}
return( *this );
}
// basic comparison operators
bool operator!=(CAutoPtr<T>& p) const
{
return !operator==(p);
}
bool operator==(CAutoPtr<T>& p) const
{
return m_p==p.m_p;
}
operator T*() const throw()
{
return( m_p );
}
T* operator->() const throw()
{
ATLASSUME( m_p != NULL );
return( m_p );
}
// Attach to an existing pointer (takes ownership)
void Attach( T* p ) throw()
{
ATLASSUME( m_p == NULL );
m_p = p;
}
// Detach the pointer (releases ownership)
T* Detach() throw()
{
T* p;
p = m_p;
m_p = NULL;
return( p );
}
// Delete the object pointed to, and set the pointer to NULL
void Free() throw()
{
delete m_p;
m_p = NULL;
}
public:
T* m_p;
};
CAutoStackPtr:
/* Automatic cleanup for _malloca objects */
template< typename T >
class CAutoStackPtr
{
public:
CAutoStackPtr() throw() :
m_p( NULL )
{
}
template< typename TSrc >
CAutoStackPtr( CAutoStackPtr< TSrc >& p ) throw()
{
m_p = p.Detach(); // Transfer ownership
}
CAutoStackPtr( CAutoStackPtr< T >& p ) throw()
{
m_p = p.Detach(); // Transfer ownership
}
explicit CAutoStackPtr( T* p ) throw() :
m_p( p )
{
}
~CAutoStackPtr() throw()
{
Free();
}
// Templated version to allow pBase = pDerived
template< typename TSrc >
CAutoStackPtr< T >& operator=( CAutoStackPtr< TSrc >& p ) throw()
{
if(m_p==p.m_p)
{
// This means that two CAutoPtrs of two different types had the same m_p in them
// which is never correct
ATLASSERT(FALSE);
}
else
{
Free();
Attach( p.Detach() ); // Transfer ownership
}
return( *this );
}
CAutoStackPtr< T >& operator=( CAutoStackPtr< T >& p ) throw()
{
if(*this==p)
{
if(this!=&p)
{
// If this assert fires, it means you attempted to assign one CAutoPtr to another when they both contained
// a pointer to the same underlying object. This means a bug in your code, since your object will get
// double-deleted.
ATLASSERT(FALSE);
// For safety, we are going to detach the other CAutoPtr to avoid a double-free. Your code still
// has a bug, though.
p.Detach();
}
else
{
// Alternatively, this branch means that you are assigning a CAutoPtr to itself, which is
// pointless but permissible
// nothing to do
}
}
else
{
Free();
Attach( p.Detach() ); // Transfer ownership
}
return( *this );
}
// basic comparison operators
bool operator!=(CAutoStackPtr<T>& p) const
{
return !operator==(p);
}
bool operator==(CAutoStackPtr<T>& p) const
{
return m_p==p.m_p;
}
operator T*() const throw()
{
return( m_p );
}
T* operator->() const throw()
{
ATLASSUME( m_p != NULL );
return( m_p );
}
// Attach to an existing pointer (takes ownership)
void Attach( T* p ) throw()
{
ATLASSUME( m_p == NULL );
m_p = p;
}
// Detach the pointer (releases ownership)
T* Detach() throw()
{
T* p;
p = m_p;
m_p = NULL;
return( p );
}
// Delete the object pointed to, and set the pointer to NULL
void Free() throw()
{
/* Note: _freea only actually does anything if m_p was heap allocated
If m_p was from the stack, it wouldn't be possible to actually free it here
[wrong function] unless we got inlined. But really all we do if m_p is
stack-based is ignore it and let its alloca storage disappear at the end
of the outer function.
*/
_freea(m_p);
m_p = NULL;
}
public:
T* m_p;
};
可以看到上面代碼明顯非常重復，不知道ATL這樣寫是不是歷史原因，我們下面嘗試對它進行重構。
可以看到其實他們只是最終釋放(Free)的時候稍微有些差別，我們明顯可以把寫差別提取出來，作為一個釋放的Policy。
struct DeleteFunctor
{
template<typename T> static void Release(T* p) { delete p; }
};
struct DeleteArrayFunctor
{
template<typename T> static void Release(T* p) { delete []p; }
};
struct DeleteStackFunctor
{
template<typename T> static void Release(T* p) { _freea p; }
};
然后我們把上面的各種釋放行為作為一個模板參數傳進去就可以了，代碼如下:
template< typename T, typename ReleasePolicy>
class CAutoReleasePtr
{
public:
CAutoReleasePtr() throw() :
m_p( NULL )
{
}
template< typename TSrc >
CAutoReleasePtr( CAutoReleasePtr< TSrc >& p ) throw()
{
m_p = p.Detach(); // Transfer ownership
}
CAutoReleasePtr( CAutoReleasePtr< T >& p ) throw()
{
m_p = p.Detach(); // Transfer ownership
}
explicit CAutoReleasePtr( T* p ) throw() :
m_p( p )
{
}
~CAutoReleasePtr() throw()
{
Free();
}
// Templated version to allow pBase = pDerived
template< typename TSrc >
CAutoReleasePtr< T >& operator=( CAutoReleasePtr< TSrc >& p ) throw()
{
if(m_p==p.m_p)
{
// This means that two CAutoPtrs of two different types had the same m_p in them
// which is never correct
ATLASSERT(FALSE);
}
else
{
Free();
Attach( p.Detach() ); // Transfer ownership
}
return( *this );
}
CAutoReleasePtr< T >& operator=( CAutoReleasePtr< T >& p ) throw()
{
if(*this==p)
{
if(this!=&p)
{
// If this assert fires, it means you attempted to assign one CAutoPtr to another when they both contained
// a pointer to the same underlying object. This means a bug in your code, since your object will get
// double-deleted.
#ifdef ATL_AUTOPTR_ASSIGNMENT_ASSERT
ATLASSERT(FALSE);
#endif
// For safety, we are going to detach the other CAutoPtr to avoid a double-free. Your code still
// has a bug, though.
p.Detach();
}
else
{
// Alternatively, this branch means that you are assigning a CAutoPtr to itself, which is
// pointless but permissible
// nothing to do
}
}
else
{
Free();
Attach( p.Detach() ); // Transfer ownership
}
return( *this );
}
// basic comparison operators
bool operator!=(CAutoReleasePtr<T>& p) const
{
return !operator==(p);
}
bool operator==(CAutoReleasePtr<T>& p) const
{
return m_p==p.m_p;
}
operator T*() const throw()
{
return( m_p );
}
T* operator->() const throw()
{
ATLASSUME( m_p != NULL );
return( m_p );
}
// Attach to an existing pointer (takes ownership)
void Attach( T* p ) throw()
{
ATLASSUME( m_p == NULL );
m_p = p;
}
// Detach the pointer (releases ownership)
T* Detach() throw()
{
T* p;
p = m_p;
m_p = NULL;
return( p );
}
// Delete the object pointed to, and set the pointer to NULL
void Free() throw()
{
ReleasePolicy::Release(m_p);
m_p = NULL;
}
public:
T* m_p;
};
可以看到我們上面其實就改了一行代碼，改了下最終的釋放策略.
好，現在我們可以這樣用了:
CAutoReleasePtr<T, DeleteFunctor> p1(new int);
CAutoReleasePtr<T, DeleteArrayFunctor> p2(new int[10]);
功能是可以了，但是是不是覺得上面這樣用起來不方便，typedef一下就好了:
typedef CAutoReleasePtr<T, DeleteFunctor> CSimplePtr<T>;
typedef CAutoReleasePtr<T, DeleteArrayFunctor> CArrayPtr<T>;
typedef CAutoReleasePtr<T, DeleteStackFunctor> CStackPtr<T>;
但是我們很塊發現上面的代碼編譯都過不了。
既然typedef不行，那我們就通過繼承來生成一個新類：
template<typename T> class CSimplePtr: public CAutoReleasePtr<T, DeleteFunctor> {};
template<typename T> class CArrayPtr: public CAutoReleasePtr<T, DeleteArrayFunctor> {};
template<typename T> class CStackPtr: public CAutoReleasePtr<T, DeleteStackFunctor> {};
我們很快又發現，用不起來，我們新類的構造函數需要重寫才行。
接下來我們考慮生成一個新類，然后在內部typedef:
template<typename T>
struct CSimplePtr
{
typedef CAutoReleasePtr<T, DeleteFunctor> type;
};
template<typename T>
struct CArrayPtr
{
typedef CAutoReleasePtr<T, DeleteArrayFunctor> type;
};
template<typename T>
struct CStackPtr
{
typedef CAutoReleasePtr<T, DeleteStackFunctor> type;
};
然后這樣用:
CSimplePtr<int>::type p(new int);
CArrayPtr<int>::type p1(new int[20]);
可是這樣用和最初的用法似乎又沒多少改進....
再最后想到了用宏:
#define CSimplePtr(T) CAutoReleasePtr<T, DeleteFunctor>
#define CArrayPtr(T) CAutoReleasePtr<T, DeleteArrayFunctor>
但是用的時候太嘔心了:
CSimplePtr(int) p(new int);
CArrayPtr(int) p1(new int[20]);
最后，實在沒有什么辦法了....
不知道大家有沒有什么好方法 ？？？
posted on 2012-09-24 22:59
Richard Wei 閱讀(1927)
評論(4) 編輯 收藏 引用 所屬分類:
C++