《STL源碼剖析》---stl_uninitialized閱讀筆記

標籤：c++   stl   記憶體初始化   

這節講解在已指派但未初始化的空間上構造對象（可能是一段記憶體，構造多個對象）。 使記憶體的配置與對象的構造分離開來。在未初始化的記憶體上構造對象時，會先判斷物件類型是否是POD類型。POD全稱是Plain old data，也就是標量類型（基本類型和指標類型）或者傳統的C struct類型。POD類型有trivial的constructor、deconstructor、copy、assignment（構造、析構、複製建構函式、賦值操作符）操作，所以對POD類型採用最有效複製手法，而對non-POD類型採用最保險安全的做法。
對於non-POD類型，通常copy constructor和operator=不等價，所以要用constructor構造每個對象。
主要有四個函數：
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說明是POD類型  return copy(first, last, result);//調用STL演算法copy()}template <class InputIterator, class ForwardIterator>ForwardIterator __uninitialized_copy_aux(InputIterator first, InputIterator last,                         ForwardIterator result,                         __false_type) {//_false_type說明是non-POD類型，要一個一個的構建，無法批量進行  ForwardIterator cur = result;  __STL_TRY {    for ( ; first != last; ++first, ++cur)//一個一個的構建      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;//用來判斷是不是POD類型  return __uninitialized_copy_aux(first, last, result, is_POD());}/*調用copy constructor,複製[first, last)範圍內每一個對象，放到目的地[result, result+(last-first) )。對於char*和wchar_t*提供特殊版本，獲得更好效率具有像資料庫事物特性的commit和rollback特性，要麼構造出所有必要元素，要麼不夠造任何東西。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);}//非隨機存取迭代器類型input_iterator_tagtemplate <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));}//隨機存取的迭代器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)/*這個根據迭代器類型跳轉 _____input_iterator_tag，調用construct(……)||uninitialized_copy_n----> iterator_category(first)?判斷迭代器類型||_____random_access_iterator_tag，調用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));//判斷迭代器類型}// Valid if copy construction is equivalent to assignment, and if the//  destructor is trivial.//如果複製建構函式和賦值操作符效果相同，且解構函式時trivial的template <class ForwardIterator, class T>inline void__uninitialized_fill_aux(ForwardIterator first, ForwardIterator last,                          const T& x, __true_type)//POD類型{  fill(first, last, x);}template <class ForwardIterator, class T>void__uninitialized_fill_aux(ForwardIterator first, ForwardIterator last,                          const T& x, __false_type)//non-POD類型{  ForwardIterator cur = first;  __STL_TRY {    for ( ; cur != last; ++cur)//一個一個構建      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初始化空間[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));//判斷first是不是POD類型}// 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)。也要判斷是不是POD類型，看懂前面兩個的話，這個自然就懂了，不再贅述。*/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: