前言
从之前智能指针的介绍中可以了解到智能指针主要作用是管理内存，避免内存泄漏和悬垂指针。
之前介绍的不管是智能指针与引用计数详解还是智能指针与句柄详解，其核心就是通过一个类来管理被new出来的对象，具体的技术就是靠引用计数。
auto_ptr介绍
auto_ptr的实现原理其实就是RAII，在构造的时候获取资源，在析构的时候释放资源，并进行相关指针操作的重载，使用起来就像普通的指针。该智能指针已经在C++11中被弃用了，已经有更好的unique_ptr来代替。
官网说明：
template class auto_ptr;
Automatic Pointer [deprecated]
Note: This class template is deprecated as of C++11. unique_ptr is a new facility with a similar functionality, but with improved security (no fake copy assignments), added features (deleters) and support for arrays. See unique_ptr for additional information.
auto_ptr特点
1. auto_ptr没有使用引用计数，在复制构造函数和赋值构造函数中将对象所有权转移了。
template<typename _Tp1> auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
template<typename _Tp1>auto_ptr& operator=(auto_ptr<_Tp1>& __a) throw()
{
reset(__a.release());
return *this;
}
void reset(element_type* __p = 0) throw()
{
if (__p != _M_ptr)
{
delete _M_ptr;
_M_ptr = __p;
}
}
element_type* release() throw()
{
element_type* __tmp = _M_ptr;
_M_ptr = 0;
return __tmp;
}
因此使用该智能指针的时候要注意：
std::auto_ptr pa(new ClassA());
motherTest(pa); //该函数会导致pa的copy构造函数执行，所有权被转移
pa->…; //调用ClassA对象的方法会crash
2. auto_ptr不能指向数组，因为auto_ptr在析构的时候只是调用delete,而数组应该要调用delete[]。
auto_ptr只有一个私有成员变量_M_ptr
template<typename _Tp> class auto_ptr
{
private:
_Tp* _M_ptr;
// 其它代码省略
}
3.auto_ptr不能和标准容器（vector,list,map…)一起使用。
STL容器中的元素经常要支持拷贝，赋值等操作，在这过程中auto_ptr会传递所有权。
下一章：shared_ptr共享指针详解
扩展：刚才想上传免费资源，但是默认要花费积分，所以直接粘贴出来了，auto_ptr源码参考：
// auto_ptr implementation -*- C++ -*-
// Copyright (C) 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file backward/auto_ptr.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{memory}
*/
#ifndef _BACKWARD_AUTO_PTR_H
#define _BACKWARD_AUTO_PTR_H 1
#include <bits/c++config.h>
#include <debug/debug.h>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* A wrapper class to provide auto_ptr with reference semantics.
* For example, an auto_ptr can be assigned (or constructed from)
* the result of a function which returns an auto_ptr by value.
*
* All the auto_ptr_ref stuff should happen behind the scenes.
*/
template<typename _Tp1>
struct auto_ptr_ref
{
_Tp1* _M_ptr;
explicit
auto_ptr_ref(_Tp1* __p): _M_ptr(__p) { }
} _GLIBCXX_DEPRECATED;
/**
* @brief A simple smart pointer providing strict ownership semantics.
*
* The Standard says:
* <pre>
* An @c auto_ptr owns the object it holds a pointer to. Copying
* an @c auto_ptr copies the pointer and transfers ownership to the
* destination. If more than one @c auto_ptr owns the same object
* at the same time the behavior of the program is undefined.
*
* The uses of @c auto_ptr include providing temporary
* exception-safety for dynamically allocated memory, passing
* ownership of dynamically allocated memory to a function, and
* returning dynamically allocated memory from a function. @c
* auto_ptr does not meet the CopyConstructible and Assignable
* requirements for Standard Library <a
* href="tables.html#65">container</a> elements and thus
* instantiating a Standard Library container with an @c auto_ptr
* results in undefined behavior.
* </pre>
* Quoted from [20.4.5]/3.
*
* Good examples of what can and cannot be done with auto_ptr can
* be found in the libstdc++ testsuite.
*
* _GLIBCXX_RESOLVE_LIB_DEFECTS
* 127. auto_ptr<> conversion issues
* These resolutions have all been incorporated.
*/
template<typename _Tp>
class auto_ptr
{
private:
_Tp* _M_ptr;
public:
/// The pointed-to type.
typedef _Tp element_type;
/**
* @brief An %auto_ptr is usually constructed from a raw pointer.
* @param p A pointer (defaults to NULL).
*
* This object now @e owns the object pointed to by @a p.
*/
explicit
auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
/**
* @brief An %auto_ptr can be constructed from another %auto_ptr.
* @param a Another %auto_ptr of the same type.
*
* This object now @e owns the object previously owned by @a a,
* which has given up ownership.
*/
auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
/**
* @brief An %auto_ptr can be constructed from another %auto_ptr.
* @param a Another %auto_ptr of a different but related type.
*
* A pointer-to-Tp1 must be convertible to a
* pointer-to-Tp/element_type.
*
* This object now @e owns the object previously owned by @a a,
* which has given up ownership.
*/
template<typename _Tp1>
auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
/**
* @brief %auto_ptr assignment operator.
* @param a Another %auto_ptr of the same type.
*
* This object now @e owns the object previously owned by @a a,
* which has given up ownership. The object that this one @e
* used to own and track has been deleted.
*/
auto_ptr&
operator=(auto_ptr& __a) throw()
{
reset(__a.release());
return *this;
}
/**
* @brief %auto_ptr assignment operator.
* @param a Another %auto_ptr of a different but related type.
*
* A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
*
* This object now @e owns the object previously owned by @a a,
* which has given up ownership. The object that this one @e
* used to own and track has been deleted.
*/
template<typename _Tp1>
auto_ptr&
operator=(auto_ptr<_Tp1>& __a) throw()
{
reset(__a.release());
return *this;
}
/**
* When the %auto_ptr goes out of scope, the object it owns is
* deleted. If it no longer owns anything (i.e., @c get() is
* @c NULL), then this has no effect.
*
* The C++ standard says there is supposed to be an empty throw
* specification here, but omitting it is standard conforming. Its
* presence can be detected only if _Tp::~_Tp() throws, but this is
* prohibited. [17.4.3.6]/2
*/
~auto_ptr() { delete _M_ptr; }
/**
* @brief Smart pointer dereferencing.
*
* If this %auto_ptr no longer owns anything, then this
* operation will crash. (For a smart pointer, <em>no longer owns
* anything</em> is the same as being a null pointer, and you know
* what happens when you dereference one of those...)
*/
element_type&
operator*() const throw()
{
_GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
return *_M_ptr;
}
/**
* @brief Smart pointer dereferencing.
*
* This returns the pointer itself, which the language then will
* automatically cause to be dereferenced.
*/
element_type*
operator->() const throw()
{
_GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
return _M_ptr;
}
/**
* @brief Bypassing the smart pointer.
* @return The raw pointer being managed.
*
* You can get a copy of the pointer that this object owns, for
* situations such as passing to a function which only accepts
* a raw pointer.
*
* @note This %auto_ptr still owns the memory.
*/
element_type*
get() const throw() { return _M_ptr; }
/**
* @brief Bypassing the smart pointer.
* @return The raw pointer being managed.
*
* You can get a copy of the pointer that this object owns, for
* situations such as passing to a function which only accepts
* a raw pointer.
*
* @note This %auto_ptr no longer owns the memory. When this object
* goes out of scope, nothing will happen.
*/
element_type*
release() throw()
{
element_type* __tmp = _M_ptr;
_M_ptr = 0;
return __tmp;
}
/**
* @brief Forcibly deletes the managed object.
* @param p A pointer (defaults to NULL).
*
* This object now @e owns the object pointed to by @a p. The
* previous object has been deleted.
*/
void
reset(element_type* __p = 0) throw()
{
if (__p != _M_ptr)
{
delete _M_ptr;
_M_ptr = __p;
}
}
/**
* @brief Automatic conversions
*
* These operations convert an %auto_ptr into and from an auto_ptr_ref
* automatically as needed. This allows constructs such as
* @code
* auto_ptr<Derived> func_returning_auto_ptr(.....);
* ...
* auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
* @endcode
*/
auto_ptr(auto_ptr_ref<element_type> __ref) throw()
: _M_ptr(__ref._M_ptr) { }
auto_ptr&
operator=(auto_ptr_ref<element_type> __ref) throw()
{
if (__ref._M_ptr != this->get())
{
delete _M_ptr;
_M_ptr = __ref._M_ptr;
}
return *this;
}
template<typename _Tp1>
operator auto_ptr_ref<_Tp1>() throw()
{ return auto_ptr_ref<_Tp1>(this->release()); }
template<typename _Tp1>
operator auto_ptr<_Tp1>() throw()
{ return auto_ptr<_Tp1>(this->release()); }
} _GLIBCXX_DEPRECATED;
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 541. shared_ptr template assignment and void
template<>
class auto_ptr<void>
{
public:
typedef void element_type;
} _GLIBCXX_DEPRECATED;
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif /* _BACKWARD_AUTO_PTR_H */
