看到ATL中有3个类的代码比较比较重复，在atlbase.h中，分别是CAutoVectorPtr, CAutoPtr和CAutoStackPtr，他们的功能其实很类似STL中的autoptr, 但是这里因为针对不同的分配对象而用了3个不同的类，其中CAutoVectorPtr是针对数组类型的，CAutoPtr是针对普通的非数组类型，而CAutoStackPtr针对的是_malloca分配的类型，因为最后释放方式的不同，它这里用了3份代码来实现。
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;
};
可以看到上面代码明显非常重复，不知道ATL这样写是不是历史原因，我们下面尝试对它进行重构。
可以看到其实他们只是最终释放(Free)的时候稍微有些差别，我们明显可以把写差别提取出来，作为一个释放的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; }
};
然后我们把上面的各种释放行为作为一个模板参数传进去就可以了，代码如下:
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;
};
可以看到我们上面其实就改了一行代码，改了下最终的释放策略.
好，现在我们可以这样用了:
CAutoReleasePtr<T, DeleteFunctor> p1(new int);
CAutoReleasePtr<T, DeleteArrayFunctor> p2(new int[10]);
功能是可以了，但是是不是觉得上面这样用起来不方便，typedef一下就好了:
typedef CAutoReleasePtr<T, DeleteFunctor> CSimplePtr<T>;
typedef CAutoReleasePtr<T, DeleteArrayFunctor> CArrayPtr<T>;
typedef CAutoReleasePtr<T, DeleteStackFunctor> CStackPtr<T>;
但是我们很块发现上面的代码编译都过不了。
既然typedef不行，那我们就通过继承来生成一个新类：
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> {};
我们很快又发现，用不起来，我们新类的构造函数需要重写才行。
接下来我们考虑生成一个新类，然后在内部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;
};
然后这样用:
CSimplePtr<int>::type p(new int);
CArrayPtr<int>::type p1(new int[20]);
可是这样用和最初的用法似乎又没多少改进....
再最后想到了用宏:
#define CSimplePtr(T) CAutoReleasePtr<T, DeleteFunctor>
#define CArrayPtr(T) CAutoReleasePtr<T, DeleteArrayFunctor>
但是用的时候太呕心了:
CSimplePtr(int) p(new int);
CArrayPtr(int) p1(new int[20]);
最后，实在没有什么办法了....
不知道大家有没有什么好方法 ？？？
posted on 2012-09-24 22:59
Richard Wei 阅读(1852)
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