auto_ptr 實(shí)現(xiàn)代碼
auto_ptr實(shí)現(xiàn)代碼 (摘自<<More Effective c++>> Page 293)2006年09月11日 星期一 20:24template <class T>
class auto_ptr
{
public:
explicit auto_ptr(T*p = 0) : pointee(p){}
template<class U> auto_ptr(auto_ptr<U>& r);
~auto_ptr(){delete pointee;}
template<class U> auto_ptr<T>& operator=(auto_ptr<U>& r);
T& operator*() const {return *pointee;}
T* operator->() const {return pointee;}
T* get() const {return pointee;}
T* release(){
T* old = pointee;
pointee = 0;
return old;
}
void reset(T*p = 0){
if(pointee != p) {
delete pointee;
pointee = p;
}
}
private:
T* pointee;
template<class U> friend class auto_ptr<U>;
};
template<class T>
template<class U>
inline auto_ptr<T>::auto_ptr(auto_ptr<U>& r)
: pointee(r.release()) {}
template<class T>
template<class U>
inline auto_ptr<T>& operator=(auto_ptr<U>& r){
if(this != &r) reset(r.release());
return *this;
}
另外 SGI C++中的auto_ptr
/*
* Copyright (c) 1997
* Silicon Graphics Computer Systems, Inc.
*
* Permission to use, copy, modify, distribute and sell this software
* and its documentation for any purpose is hereby granted without fee,
* provided that the above copyright notice appear in all copies and
* that both that copyright notice and this permission notice appear
* in supporting documentation. Silicon Graphics makes no
* representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied warranty.
*
*/
#ifndef __SGI_STL_MEMORY
#define __SGI_STL_MEMORY
#include <stl_algobase.h>
#include <stl_alloc.h>
#include <stl_construct.h>
#include <stl_tempbuf.h>
#include <stl_uninitialized.h>
#include <stl_raw_storage_iter.h>
#if defined(__STL_MEMBER_TEMPLATES)
__STL_BEGIN_NAMESPACE
template <class _Tp> class auto_ptr {
private:
_Tp* _M_ptr;
public:
typedef _Tp element_type;
explicit auto_ptr(_Tp* __p = 0) __STL_NOTHROW : _M_ptr(__p) {}
auto_ptr(auto_ptr& __a) __STL_NOTHROW : _M_ptr(__a.release()) {}
template <class _Tp1> auto_ptr(auto_ptr<_Tp1>& __a) __STL_NOTHROW
: _M_ptr(__a.release()) {}
auto_ptr& operator=(auto_ptr& __a) __STL_NOTHROW {
if (&__a != this) {
delete _M_ptr;
_M_ptr = __a.release();
}
return *this;
}
template <class _Tp1>
auto_ptr& operator=(auto_ptr<_Tp1>& __a) __STL_NOTHROW {
if (__a.get() != this->get()) {
delete _M_ptr;
_M_ptr = __a.release();
}
return *this;
}
~auto_ptr() __STL_NOTHROW { delete _M_ptr; }
_Tp& operator*() const __STL_NOTHROW {
return *_M_ptr;
}
_Tp* operator->() const __STL_NOTHROW {
return _M_ptr;
}
_Tp* get() const __STL_NOTHROW {
return _M_ptr;
}
_Tp* release() __STL_NOTHROW {
_Tp* __tmp = _M_ptr;
_M_ptr = 0;
return __tmp;
}
void reset(_Tp* __p = 0) __STL_NOTHROW {
delete _M_ptr;
_M_ptr = __p;
}
// According to the C++ standard, these conversions are required. Most
// present-day compilers, however, do not enforce that requirement---and,
// in fact, most present-day compilers do not support the language
// features that these conversions rely on.
#ifdef __SGI_STL_USE_AUTO_PTR_CONVERSIONS
private:
template<class _Tp1> struct auto_ptr_ref {
_Tp1* _M_ptr;
auto_ptr_ref(_Tp1* __p) : _M_ptr(__p) {}
};
public:
auto_ptr(auto_ptr_ref<_Tp> __ref) __STL_NOTHROW
: _M_ptr(__ref._M_ptr) {}
template <class _Tp1> operator auto_ptr_ref<_Tp1>() __STL_NOTHROW
{ return auto_ptr_ref<_Tp>(this->release()); }
template <class _Tp1> operator auto_ptr<_Tp1>() __STL_NOTHROW
{ return auto_ptr<_Tp1>(this->release()); }
#endif /* __SGI_STL_USE_AUTO_PTR_CONVERSIONS */
};
__STL_END_NAMESPACE
#endif /* member templates */
#endif /* __SGI_STL_MEMORY */
// Local Variables:
// mode:C++
// End:
auto_ptr 注意事項(xiàng)
1.auto_ptr不能共享管理的指針的所有權(quán)，并且指針是從堆上分配的
2.不能用于管理指針數(shù)組，因?yàn)樗谖鰳?gòu)的時(shí)候調(diào)用的是delete而不是delete[]；并且c++類庫中還沒有具有auto_ptr語意學(xué)的指針數(shù)組。
3.auto_ptr是解決特殊問題的智能指針的一種，它和引入了引用記數(shù)的是智能指針是不一樣的，一般來講，根據(jù)auto_ptr的特性，應(yīng)用unconstant是一種不安全的做法。
4.它不能應(yīng)用容器中，因?yàn)檫@會(huì)涉及到copy以及assignment，這是不安全的，在語言以及庫中已經(jīng)做了預(yù)防，會(huì)在編譯時(shí)報(bào)錯(cuò)。
總體來說如果把a(bǔ)uto_ptr作為函數(shù)自變量或者返回值來用的話，就好像把函數(shù)內(nèi)棧上分配的空間地址返回，很不安全。