《STL源码剖析》---stl_uninitialized阅读笔记

这节讲解在已分配但未初始化的空间上构造对象（可能是一段内存，构造多个对象）。 使内存的配置与对象的构造分离开来。在未初始化的内存上构造对象时，会先判断对象类型是否是POD类型。POD全称是Plain old data，也就是标量类型（基本类型和指针类型）或者传统的C struct类型。POD类型有trivial的constructor、deconstructor、copy、assignment（构造、析构、复制构造函数、赋值操作符）操作，所以对POD类型采用最有效的复制手法，而对non-POD类型采用最保险安全的做法。

对于non-POD类型，通常copy constructor和operator=不等价，所以要用constructor构造每个对象。

主要有四个函数：

1、uninitialized_copy

2、uninitialized_copy_n

3、uninitialized_fill

4、uninitialized_fill_n

G++ 2.91.57，cygnus\cygwin-b20\include\g++\stl_uninitialized.h 完整列表

/*
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * 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.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1996,1997
 * 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.
 */

/* NOTE: This is an internal header file, included by other STL headers.
 *   You should not attempt to use it directly.
 */

#ifndef __SGI_STL_INTERNAL_UNINITIALIZED_H
#define __SGI_STL_INTERNAL_UNINITIALIZED_H

__STL_BEGIN_NAMESPACE

// Valid if copy construction is equivalent to assignment, and if the
//  destructor is trivial.
template <class InputIterator, class ForwardIterator>
inline ForwardIterator
__uninitialized_copy_aux(InputIterator first, InputIterator last,
                         ForwardIterator result,
                         __true_type) {//_true_type说明是POD类型
  return copy(first, last, result);//调用STL算法copy()
}

template <class InputIterator, class ForwardIterator>
ForwardIterator
__uninitialized_copy_aux(InputIterator first, InputIterator last,
                         ForwardIterator result,
                         __false_type) {//_false_type说明是non-POD类型，要一个一个的构建，无法批量进行
  ForwardIterator cur = result;
  __STL_TRY {
    for ( ; first != last; ++first, ++cur)//一个一个的构建
      construct(&*cur, *first);
    return cur;
  }
  __STL_UNWIND(destroy(result, cur));
}

template <class InputIterator, class ForwardIterator, class T>
inline ForwardIterator
__uninitialized_copy(InputIterator first, InputIterator last,
                     ForwardIterator result, T*) {
  typedef typename __type_traits<T>::is_POD_type is_POD;//用来判断是不是POD类型
  return __uninitialized_copy_aux(first, last, result, is_POD());
}
/*
调用copy constructor,复制[first, last)范围内每一个对象，放到目的地[result, result+(last-first) )。
对于char*和wchar_t*提供特殊版本，获得更好效率
具有像数据库事物特性的commit和rollback特性，要么构造出所有必要元素，要么不够造任何东西。

		copy()               for(; first!=last) construct()
		|						  |
		| _true_type			  | _false_type
        <__特化____________特化__>
				   |
			_uninitialized_copy()
 <InputIterator, Inputterator, ForwardIterator>
				   |
				   |泛化
				   |
uninitialized _____|_____特化___>(const char*, const char*,char*) memmove()
_copy()			   |
				   |
    			   |____特化___>(const wchar_t*, const wchar_t*, wchar_t*) memmove()

*/
template <class InputIterator, class ForwardIterator>
inline ForwardIterator
  uninitialized_copy(InputIterator first, InputIterator last,
                     ForwardIterator result) {
  return __uninitialized_copy(first, last, result, value_type(result));
}
//char*版本
inline char* uninitialized_copy(const char* first, const char* last,
                                char* result) {
  memmove(result, first, last - first);
  return result + (last - first);
}
//wchar_t*版本
inline wchar_t* uninitialized_copy(const wchar_t* first, const wchar_t* last,
                                   wchar_t* result) {
  memmove(result, first, sizeof(wchar_t) * (last - first));
  return result + (last - first);
}

//非随机存取迭代器类型input_iterator_tag
template <class InputIterator, class Size, class ForwardIterator>
pair<InputIterator, ForwardIterator>
__uninitialized_copy_n(InputIterator first, Size count,
                       ForwardIterator result,
                       input_iterator_tag) {
  ForwardIterator cur = result;
  __STL_TRY {
    for ( ; count > 0 ; --count, ++first, ++cur)
      construct(&*cur, *first);
    return pair<InputIterator, ForwardIterator>(first, cur);
  }
  __STL_UNWIND(destroy(result, cur));
}
//随机存取的迭代器
template <class RandomAccessIterator, class Size, class ForwardIterator>
inline pair<RandomAccessIterator, ForwardIterator>
__uninitialized_copy_n(RandomAccessIterator first, Size count,
                       ForwardIterator result,
                       random_access_iterator_tag) {
  RandomAccessIterator last = first + count;
  return make_pair(last, uninitialized_copy(first, last, result));
}
//用[result, result+count)初始化[first, first+cout)
/*
这个根据迭代器类型跳转
						 _____input_iterator_tag，调用construct(……)
						|
						|
uninitialized_copy_n----> iterator_category(first)?判断迭代器类型
						|
						|_____random_access_iterator_tag，调用uninitialized_copy(……)
*/
template <class InputIterator, class Size, class ForwardIterator>
inline pair<InputIterator, ForwardIterator>
uninitialized_copy_n(InputIterator first, Size count,
                     ForwardIterator result) {
  return __uninitialized_copy_n(first, count, result,
                                iterator_category(first));//判断迭代器类型
}

// Valid if copy construction is equivalent to assignment, and if the
//  destructor is trivial.
//如果复制构造函数和赋值操作符效果相同，且析构函数时trivial的
template <class ForwardIterator, class T>
inline void
__uninitialized_fill_aux(ForwardIterator first, ForwardIterator last,
                         const T& x, __true_type)//POD类型
{
  fill(first, last, x);
}

template <class ForwardIterator, class T>
void
__uninitialized_fill_aux(ForwardIterator first, ForwardIterator last,
                         const T& x, __false_type)//non-POD类型
{
  ForwardIterator cur = first;
  __STL_TRY {
    for ( ; cur != last; ++cur)//一个一个构建
      construct(&*cur, x);
  }
  __STL_UNWIND(destroy(first, cur));
}

template <class ForwardIterator, class T, class T1>
inline void __uninitialized_fill(ForwardIterator first, ForwardIterator last,
                                 const T& x, T1*) {
  typedef typename __type_traits<T1>::is_POD_type is_POD;
  __uninitialized_fill_aux(first, last, x, is_POD());

}

/*
用x初始化空间[first, last)
						___>  construct(……)
						| __false_type
						|
uninitialized_fill------> is POD?
						|   __true_type
						|___>   fill(……)

*/

template <class ForwardIterator, class T>
inline void uninitialized_fill(ForwardIterator first, ForwardIterator last,
                               const T& x) {
  __uninitialized_fill(first, last, x, value_type(first));//判断first是不是POD类型
}

// Valid if copy construction is equivalent to assignment, and if the
//  destructor is trivial.
template <class ForwardIterator, class Size, class T>
inline ForwardIterator
__uninitialized_fill_n_aux(ForwardIterator first, Size n,
                           const T& x, __true_type) {
  return fill_n(first, n, x);
}

template <class ForwardIterator, class Size, class T>
ForwardIterator
__uninitialized_fill_n_aux(ForwardIterator first, Size n,
                           const T& x, __false_type) {
  ForwardIterator cur = first;
  __STL_TRY {
    for ( ; n > 0; --n, ++cur)
      construct(&*cur, x);
    return cur;
  }
  __STL_UNWIND(destroy(first, cur));
}

template <class ForwardIterator, class Size, class T, class T1>
inline ForwardIterator __uninitialized_fill_n(ForwardIterator first, Size n,
                                              const T& x, T1*) {
  typedef typename __type_traits<T1>::is_POD_type is_POD;
  return __uninitialized_fill_n_aux(first, n, x, is_POD());

}
/*
用x初始化[first, first+n)。也要判断是不是POD类型，看懂前面两个的话，这个自然就懂了，不再赘述。
*/
template <class ForwardIterator, class Size, class T>
inline ForwardIterator uninitialized_fill_n(ForwardIterator first, Size n,
                                            const T& x) {
  return __uninitialized_fill_n(first, n, x, value_type(first));
}

// Copies [first1, last1) into [result, result + (last1 - first1)), and
//  copies [first2, last2) into
//  [result, result + (last1 - first1) + (last2 - first2)).

template <class InputIterator1, class InputIterator2, class ForwardIterator>
inline ForwardIterator
__uninitialized_copy_copy(InputIterator1 first1, InputIterator1 last1,
                          InputIterator2 first2, InputIterator2 last2,
                          ForwardIterator result) {
  ForwardIterator mid = uninitialized_copy(first1, last1, result);
  __STL_TRY {
    return uninitialized_copy(first2, last2, mid);
  }
  __STL_UNWIND(destroy(result, mid));
}

// Fills [result, mid) with x, and copies [first, last) into
//  [mid, mid + (last - first)).
template <class ForwardIterator, class T, class InputIterator>
inline ForwardIterator
__uninitialized_fill_copy(ForwardIterator result, ForwardIterator mid,
                          const T& x,
                          InputIterator first, InputIterator last) {
  uninitialized_fill(result, mid, x);
  __STL_TRY {
    return uninitialized_copy(first, last, mid);
  }
  __STL_UNWIND(destroy(result, mid));
}

// Copies [first1, last1) into [first2, first2 + (last1 - first1)), and
//  fills [first2 + (last1 - first1), last2) with x.
template <class InputIterator, class ForwardIterator, class T>
inline void
__uninitialized_copy_fill(InputIterator first1, InputIterator last1,
                          ForwardIterator first2, ForwardIterator last2,
                          const T& x) {
  ForwardIterator mid2 = uninitialized_copy(first1, last1, first2);
  __STL_TRY {
    uninitialized_fill(mid2, last2, x);
  }
  __STL_UNWIND(destroy(first2, mid2));
}

__STL_END_NAMESPACE

#endif /* __SGI_STL_INTERNAL_UNINITIALIZED_H */

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

《STL源码剖析》---stl_uninitialized阅读笔记