析构时候清除pointer
template <typename T>
struct QScopedPointerDeleter
{
static inline void cleanup(T *pointer)
{
// Enforce a complete type.
// If you get a compile error here, read the secion on forward declared
// classes in the QScopedPointer documentation.
//检查类型是否完整，编译期间检查
typedef char IsIncompleteType[ sizeof(T) ? 1 : -1 ];
(void) sizeof(IsIncompleteType);
delete pointer;
}
};
template <typename T>
struct QScopedPointerArrayDeleter
{
static inline void cleanup(T *pointer)
{
// Enforce a complete type.
// If you get a compile error here, read the secion on forward declared
// classes in the QScopedPointer documentation.
typedef char IsIncompleteType[ sizeof(T) ? 1 : -1 ];
(void) sizeof(IsIncompleteType);
delete [] pointer;
}
};
struct QScopedPointerPodDeleter
{
static inline void cleanup(void *pointer) { if (pointer) qFree(pointer); }
};
template <typename T, typename Cleanup = QScopedPointerDeleter<T> >
class QScopedPointer
{
#ifndef Q_CC_NOKIAX86
typedef T *QScopedPointer:: *RestrictedBool;
#endif
public:
explicit inline QScopedPointer(T *p = 0) : d(p)
{
}
inline ~QScopedPointer()
{
T *oldD = this->d;
Cleanup::cleanup(oldD);
this->d = 0;
}
inline T &operator*() const
{
Q_ASSERT(d);
return *d;
}
inline T *operator->() const
{
Q_ASSERT(d);
return d;
}
inline bool operator!() const
{
return !d;
}
#if defined(Q_CC_NOKIAX86) || defined(Q_QDOC)
inline operator bool() const
{
return isNull() ? 0 : &QScopedPointer::d;
}
#else
inline operator RestrictedBool() const
{
return isNull() ? 0 : &QScopedPointer::d;
}
#endif
inline T *data() const
{
return d;
}
inline bool isNull() const
{
return !d;
}
inline void reset(T *other = 0)
{
if (d == other)
return;
T *oldD = d;
d = other;
Cleanup::cleanup(oldD);
}
inline T *take()
{
T *oldD = d;
d = 0;
return oldD;
}
inline void swap(QScopedPointer<T, Cleanup> &other)
{
qSwap(d, other.d);
}
typedef T *pointer;
protected:
T *d;
private:
Q_DISABLE_COPY(QScopedPointer)
};
template <class T, class Cleanup>
inline bool operator==(const QScopedPointer<T, Cleanup> &lhs, const QScopedPointer<T, Cleanup> &rhs)
{
return lhs.data() == rhs.data();
}
template <class T, class Cleanup>
inline bool operator!=(const QScopedPointer<T, Cleanup> &lhs, const QScopedPointer<T, Cleanup> &rhs)
{
return lhs.data() != rhs.data();
}
template <class T, class Cleanup>
Q_INLINE_TEMPLATE void qSwap(QScopedPointer<T, Cleanup> &p1, QScopedPointer<T, Cleanup> &p2)
{ p1.swap(p2); }
template <typename T, typename Cleanup = QScopedPointerArrayDeleter<T> >
class QScopedArrayPointer : public QScopedPointer<T, Cleanup>
{
public:
explicit inline QScopedArrayPointer(T *p = 0)
: QScopedPointer<T, Cleanup>(p)
{
}
inline T &operator[](int i)
{
return this->d[i];
}
inline const T &operator[](int i) const
{
return this->d[i];
}
private:
Q_DISABLE_COPY(QScopedArrayPointer)
};
#define Q_DISABLE_COPY(Class) \
Class(const Class &); \
Class &operator=(const Class &);
声明拷贝和赋值函数为私有
--------------------------------
参考
C++ template Day Day Up 第四天 Boost::checked_delete
//DeleteObject.h
class Item;
class DeleteObject
{
public:
DeleteObject(void);
public:
~DeleteObject(void);
void DeleteItem(Item* p);
};
//DeleteObject.cpp
#include "StdAfx.h"
#include "DeleteObject.h"
#include <boost/checked_delete.hpp>
DeleteObject::DeleteObject(void)
{
}
DeleteObject::~DeleteObject(void)
{
}
void DeleteObject::DeleteItem( Item* p )
{
delete p;
}
//item.h
#include <iostream>
class Item
{
public:
~Item()
{
std::cout<<"Item destruction ";
}
};
//main.cpp
#include "DeleteObject.h"
#include "Item.h"
DeleteObject del;
del.DeleteItem(new Item);
/////////////////////////////////
结果Item的析构函数没有被调用~
这是因为DeleteObject并不知道Item的详细定义，这是C++中一个很危险的错误！（还好编译器一般都给warning）
怎么解决这个问题呢？
利用Boost库中的checked_delete
定义如下：
template<class T> inline void checked_delete(T * x)
{
// intentionally complex - simplification causes regressions
typedef char type_must_be_complete[ sizeof(T)? 1: -1 ];
(void) sizeof(type_must_be_complete);
delete x;
}
template<class T> inline void checked_array_delete(T * x)
{
typedef char type_must_be_complete[ sizeof(T)? 1: -1 ];
(void) sizeof(type_must_be_complete);
delete [] x;
}
可以看到利用C的一个语法——数组长度必须大于零，来解决这个问题，typedef是发生在编译期，而sizeof同样是在编译期，所以这两行代码不会对程序的效率空间等等产生任何影响，只会在上面所举的例子发生的时候报编译错误。
现在将代码改为：
void DeleteObject::DeleteItem( Item* p )
{
boost::checked_delete(p);
}
