Boost源码学习---scoped_ptr.hpp

scoped_ptr是一个智能指针，包装了指向堆上内存的指针。它对指针所有权加以限制，不能转让指针所有权，一旦scoped_ptr获取了指针的管理权，便不再释放，无法再从其取回来，就像scope意思一样，指针智能在作用域使用，不能转让出去。一旦离开scoped_ptr的作用域，将调用它的析构函数，释放指针，不用手动释放。下面是它的源代码：

#ifndef BOOST_SMART_PTR_SCOPED_PTR_HPP_INCLUDED#define BOOST_SMART_PTR_SCOPED_PTR_HPP_INCLUDED//  (C) Copyright Greg Colvin and Beman Dawes 1998, 1999.//  Copyright (c) 2001, 2002 Peter Dimov////  Distributed under the Boost Software License, Version 1.0. (See//  accompanying file LICENSE_1_0.txt or copy at//  http://www.boost.org/LICENSE_1_0.txt)////  http://www.boost.org/libs/smart_ptr/scoped_ptr.htm//#include <boost/config.hpp>#include <boost/assert.hpp>#include <boost/checked_delete.hpp>#include <boost/smart_ptr/detail/sp_nullptr_t.hpp>#include <boost/detail/workaround.hpp>#ifndef BOOST_NO_AUTO_PTR# include <memory>          // for std::auto_ptr#endifnamespace boost{// Debug hooks#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)void sp_scalar_constructor_hook(void * p);void sp_scalar_destructor_hook(void * p);#endif//  scoped_ptr mimics a built-in pointer except that it guarantees deletion//  of the object pointed to, either on destruction of the scoped_ptr or via//  an explicit reset(). scoped_ptr is a simple solution for simple needs;//  use shared_ptr or std::auto_ptr if your needs are more complex.template<class T> class scoped_ptr // noncopyable{private:    T * px;//原生态指针//将复制构造函数和赋值操作符声明为私有，不允许在类外使用，这样就限制了其所有权的转让    scoped_ptr(scoped_ptr const &);    scoped_ptr & operator=(scoped_ptr const &);    typedef scoped_ptr<T> this_type;//重载为私有，不支持比较    void operator==( scoped_ptr const& ) const;    void operator!=( scoped_ptr const& ) const;public:    typedef T element_type;//显示构造函数，必须显示调用    explicit scoped_ptr( T * p = 0 ): px( p ) // never throws    {#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)        boost::sp_scalar_constructor_hook( px );#endif    }#ifndef BOOST_NO_AUTO_PTR//参数为auto_ptr时的构造函数//p.release()设auto_ptr为NULL，返回其内部指针    explicit scoped_ptr( std::auto_ptr<T> p ) BOOST_NOEXCEPT : px( p.release() )    {#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)        boost::sp_scalar_constructor_hook( px );#endif    }#endif//析构函数，析构对象，释放内存    ~scoped_ptr() // never throws    {#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)        boost::sp_scalar_destructor_hook( px );#endif        boost::checked_delete( px );    }    void reset(T * p = 0) // never throws    {        BOOST_ASSERT( p == 0 || p != px ); // catch self-reset errors        //把p转换为scoped_prt，再调用swap交换        this_type(p).swap(*this);    }//重载解引用，返回指针指向的对象    T & operator*() const // never throws    {        BOOST_ASSERT( px != 0 );        return *px;    }//重载->，返回指针    T * operator->() const // never throws    {        BOOST_ASSERT( px != 0 );        return px;    }//返回指针    T * get() const BOOST_NOEXCEPT    {        return px;    }// implicit conversion to "bool"#include <boost/smart_ptr/detail/operator_bool.hpp>//交换两个指针    void swap(scoped_ptr & b) BOOST_NOEXCEPT    {        T * tmp = b.px;        b.px = px;        px = tmp;    }};#if !defined( BOOST_NO_CXX11_NULLPTR )template<class T> inline bool operator==( scoped_ptr<T> const & p, boost::detail::sp_nullptr_t ) BOOST_NOEXCEPT{    return p.get() == 0;}template<class T> inline bool operator==( boost::detail::sp_nullptr_t, scoped_ptr<T> const & p ) BOOST_NOEXCEPT{    return p.get() == 0;}template<class T> inline bool operator!=( scoped_ptr<T> const & p, boost::detail::sp_nullptr_t ) BOOST_NOEXCEPT{    return p.get() != 0;}template<class T> inline bool operator!=( boost::detail::sp_nullptr_t, scoped_ptr<T> const & p ) BOOST_NOEXCEPT{    return p.get() != 0;}#endiftemplate<class T> inline void swap(scoped_ptr<T> & a, scoped_ptr<T> & b) BOOST_NOEXCEPT{    a.swap(b);}// get_pointer(p) is a generic way to say p.get()template<class T> inline T * get_pointer(scoped_ptr<T> const & p) BOOST_NOEXCEPT{    return p.get();}} // namespace boost#endif // #ifndef BOOST_SMART_PTR_SCOPED_PTR_HPP_INCLUDED

scoped_ptr与auto_ptr不同的是：auto_ptr可以转让使用权，在转让的时候，上一个指针失去使用权。而scoped_ptr不允许转让使用权。

scoped_ptr和auto_ptr都不能放在容器，auto_ptr是因为它只允许一个auto_prt使用指针，而scoped_ptr是因为不允许转让使用权，不支持拷贝和复制，不符合容器对元素的要求。