auto_ptr源码实现

本文地址：http://blog.youkuaiyun.com/spch2008/article/details/8996339

Exception specifications

  void fun() throw(){}

  只是一种标识，约定该函数不应该抛出异常。

  1. 如果该函数内部有throw语句，即直接抛出异常，则编译出错。

  2. 如果该函数内部调用另一个函数，而此函数内部有throw语句，则编译器无法发现，运行时候抛出异常。

Cygnus实现

 1.  stl_config.h 中配置信息 

     

# ifdef __STL_USE_EXCEPTIONS
#   define __STL_TRY try
#   define __STL_CATCH_ALL catch(...)
#   define __STL_RETHROW throw
#   define __STL_NOTHROW throw()
#   define __STL_UNWIND(action) catch(...) { action; throw; }
# else
#   define __STL_TRY 
#   define __STL_CATCH_ALL if (false)
#   define __STL_RETHROW 
#   define __STL_NOTHROW 
#   define __STL_UNWIND(action) 
# endif

# if defined(__STL_USE_NAMESPACES) && !defined(__STL_NO_NAMESPACES)
#   define __STD std
#   define __STL_BEGIN_NAMESPACE namespace std {
#   define __STL_END_NAMESPACE }
#   define  __STL_USE_NAMESPACE_FOR_RELOPS
#   define __STL_BEGIN_RELOPS_NAMESPACE namespace std {
#   define __STL_END_RELOPS_NAMESPACE }
#   define __STD_RELOPS std
# else
#   define __STD 
#   define __STL_BEGIN_NAMESPACE 
#   define __STL_END_NAMESPACE 
#   undef  __STL_USE_NAMESPACE_FOR_RELOPS
#   define __STL_BEGIN_RELOPS_NAMESPACE 
#   define __STL_END_RELOPS_NAMESPACE 
#   define __STD_RELOPS 
# endif

   auto_ptr代码实现

/*
 * 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>

// Note: auto_ptr is commented out in this release because the details
//  of the interface are still being discussed by the C++ standardization
//  committee.  It will be included once the iterface is finalized.

#if 0
#if defined(_MUTABLE_IS_KEYWORD) && defined(_EXPLICIT_IS_KEYWORD) && \
    defined(__STL_MEMBER_TEMPLATES)

//命名空间
__STL_BEGIN_NAMESPACE

template <class X> 
class auto_ptr 
{
private:
  X* ptr;
  mutable bool owns;
public:
  typedef X element_type;

  //explicit不运行进行隐式转换，即不允许 auto_ptr<A> ptr = new A;
  explicit auto_ptr(X* p = 0) __STL_NOTHROW : ptr(p), owns(p) {}
  auto_ptr(const auto_ptr& a) __STL_NOTHROW : ptr(a.ptr), owns(a.owns) 
  {
    a.owns = 0;
  }
  
  template <class T> 
  auto_ptr(const auto_ptr<T>& a) __STL_NOTHROW
    : ptr(a.ptr), owns(a.owns) 
  {
      a.owns = 0;
  }

  auto_ptr& operator=(const auto_ptr& a) __STL_NOTHROW 
  {
    if (&a != this) 
    {
      if (owns)
        delete ptr;
      owns = a.owns;
      ptr = a.ptr;
      a.owns = 0;
    }
    //没有返回？
  }
  
  //该函数用于支持相关类型之间的相互赋值
  //即类型T可以转换成类型X。比如：X基类，T派生类
  template <class T> 
  auto_ptr& operator=(const auto_ptr<T>& a) __STL_NOTHROW 
  {
    if (&a != this) 
    {
      if (owns)
        delete ptr;
      owns = a.owns;
      ptr = a.ptr;
      a.owns = 0;
    }
    //这里没有返回，代码是否正确？
  }

  ~auto_ptr() 
  {
    if (owns)
      delete ptr;
  }

  X& operator*() const __STL_NOTHROW { return *ptr; }
  X* operator->() const __STL_NOTHROW { return ptr; }
  X* get() const __STL_NOTHROW { return ptr; }
  X* release const __STL_NOTHROW { owns = false; return ptr }  //没有分号？
};

__STL_END_NAMESPACE
#endif /* mutable && explicit && member templates */
#endif /* 0 */


#endif /* __SGI_STL_MEMORY */


// Local Variables:
// mode:C++
// End:

上述代码有多处不符合逻辑的地方，是代码错误还是理解有问题？

GCC实现

// auto_ptr implementation -*- C++ -*-
 
 // Copyright (C) 2007, 2008, 2009, 2010 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.
 // 代码地址：http://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-api-4.5/a00745_source.html

 
 #ifndef _BACKWARD_AUTO_PTR_H
 #define _BACKWARD_AUTO_PTR_H 1
 

template<typename _Tp>
class auto_ptr
{
 private:
     _Tp* _M_ptr;
   
 public:
     /// The pointed-to type.
     typedef _Tp element_type;
   

     explicit
     auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }

 
     auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }


     template<typename _Tp1>
     auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }


     auto_ptr& operator=(auto_ptr& __a) throw()
     {
	    reset(__a.release());
		return *this;
     }

     template<typename _Tp1>
     auto_ptr& operator=(auto_ptr<_Tp1>& __a) throw()
     {
         reset(__a.release());
         return *this;
     }


     ~auto_ptr() { delete _M_ptr; }
   
   
     element_type& operator*() const throw() 
     {
         //就相当于一个Assert
         _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
         return *_M_ptr; 
     }
   

     element_type* operator->() const throw() 
     {
       _GLIBCXX_DEBUG_ASSERT(_M_ptr != 0);
       return _M_ptr; 
     }
   
  
     element_type* get() const throw() { return _M_ptr; }
   
 
     element_type* release() throw()
     {
        element_type* __tmp = _M_ptr;
        _M_ptr = 0;
        return __tmp;
     }
   
     void reset(element_type* __p = 0) throw()
     {
         if (__p != _M_ptr)
         {
             delete _M_ptr;
             _M_ptr = __p;
         }
     }
};

#endif /* _BACKWARD_AUTO_PTR_H */