stl_uninitialized.h

最新推荐文章于 2025-09-08 21:57:50 发布

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最新推荐文章于 2025-09-08 21:57:50 发布

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CC 4.0 BY-SA版权

文章标签： c/c++

原文链接：http://www.cnblogs.com/Atela/archive/2011/10/17/2215578.html

本文详细介绍了C++中内存初始化的几种方式，包括initialized_copy、uninitialized_fill及uninitialized_fill_n等函数的实现原理和使用场景。特别是对于POD类型和其他类型的处理差异进行了深入解析。

需要时#include <memory>

1.initialized_copy对应高层函数copy();

uninitialized_fill 对应高层函数fill()

uninitialized_fill_n 对应高层函数fill_n()

都是取迭代器first的value type，判断该型别是否为POD(Plain Old Data)

其具有trvial constructor/destructor/copy constructor/operator =
所有的C++内置基本数据类型和传统C struct都属于POD

对POD型别调用高层函数，初值填写法，对non-POD采取最保险做法，每个元素分别构造。如果构造失败，需要对已构造的所有元素析构。

两个特化

char * uninitialized_copy (const char *__first, const char *__last, char *__result); 调用直接移动内存函数memmove

wchar_t * uninitialized_copy (const wchar_t *__first, const wchar_t *__last, wchar_t *__result);调用直接移动内存函数memmove

__uninitialized_copy_copy

__uninitialized_fill_copy

__uninitialized_copy_fill

3.非C++标准

template <class _InputIter, class _Size, class _ForwardIter>
pair<_InputIter, _ForwardIter>uninitialized_copy_n(_InputIter __first, _Size __count, _ForwardIter __result);

#ifndef __SGI_STL_INTERNAL_UNINITIALIZED_H
#define __SGI_STL_INTERNAL_UNINITIALIZED_H

__STL_BEGIN_NAMESPACE

// uninitialized_copy

// Valid if copy construction is equivalent to assignment, and if the
//  destructor is trivial.
template <class _InputIter, class _ForwardIter>
inline _ForwardIter 
__uninitialized_copy_aux(_InputIter __first, _InputIter __last,
                         _ForwardIter __result,
                         __true_type)
{
  return copy(__first, __last, __result);
}

template <class _InputIter, class _ForwardIter>
_ForwardIter 
__uninitialized_copy_aux(_InputIter __first, _InputIter __last,
                         _ForwardIter __result,
                         __false_type)
{
  _ForwardIter __cur = __result;
  __STL_TRY {
    for ( ; __first != __last; ++__first, ++__cur)
      _Construct(&*__cur, *__first);
    return __cur;
  }
  __STL_UNWIND(_Destroy(__result, __cur));
}


template <class _InputIter, class _ForwardIter, class _Tp>
inline _ForwardIter
__uninitialized_copy(_InputIter __first, _InputIter __last,
                     _ForwardIter __result, _Tp*)
{
  typedef typename __type_traits<_Tp>::is_POD_type _Is_POD;
  return __uninitialized_copy_aux(__first, __last, __result, _Is_POD());
}

template <class _InputIter, class _ForwardIter>
inline _ForwardIter
  uninitialized_copy(_InputIter __first, _InputIter __last,
                     _ForwardIter __result)
{
  return __uninitialized_copy(__first, __last, __result,
                              __VALUE_TYPE(__result));
}



//--------------------------------------------------------------------------------------
inline char* uninitialized_copy(const char* __first, const char* __last,
                                char* __result) {
  memmove(__result, __first, __last - __first);
  return __result + (__last - __first);
}

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);
}

//--------------------------------------------------------------------------------------

// uninitialized_copy_n (not part of the C++ standard)

template <class _InputIter, class _Size, class _ForwardIter>
pair<_InputIter, _ForwardIter>
__uninitialized_copy_n(_InputIter __first, _Size __count,
                       _ForwardIter __result,
                       input_iterator_tag)
{
  _ForwardIter __cur = __result;
  __STL_TRY {
    for ( ; __count > 0 ; --__count, ++__first, ++__cur) 
      _Construct(&*__cur, *__first);
    return pair<_InputIter, _ForwardIter>(__first, __cur);
  }
  __STL_UNWIND(_Destroy(__result, __cur));
}

template <class _RandomAccessIter, class _Size, class _ForwardIter>
inline pair<_RandomAccessIter, _ForwardIter>
__uninitialized_copy_n(_RandomAccessIter __first, _Size __count,
                       _ForwardIter __result,
                       random_access_iterator_tag) {
  _RandomAccessIter __last = __first + __count;
  return pair<_RandomAccessIter, _ForwardIter>(
                 __last,
                 uninitialized_copy(__first, __last, __result));
}

template <class _InputIter, class _Size, class _ForwardIter>
inline pair<_InputIter, _ForwardIter>
__uninitialized_copy_n(_InputIter __first, _Size __count,
                     _ForwardIter __result) {
  return __uninitialized_copy_n(__first, __count, __result,
                                __ITERATOR_CATEGORY(__first));
}

template <class _InputIter, class _Size, class _ForwardIter>
inline pair<_InputIter, _ForwardIter>
uninitialized_copy_n(_InputIter __first, _Size __count,
                     _ForwardIter __result) {
  return __uninitialized_copy_n(__first, __count, __result,
                                __ITERATOR_CATEGORY(__first));
}


//--------------------------------------------------------------------------------------
// Valid if copy construction is equivalent to assignment, and if the
// destructor is trivial.
template <class _ForwardIter, class _Tp>
inline void
__uninitialized_fill_aux(_ForwardIter __first, _ForwardIter __last, 
                         const _Tp& __x, __true_type)
{
  fill(__first, __last, __x);
}

template <class _ForwardIter, class _Tp>
void
__uninitialized_fill_aux(_ForwardIter __first, _ForwardIter __last, 
                         const _Tp& __x, __false_type)
{
  _ForwardIter __cur = __first;
  __STL_TRY {
    for ( ; __cur != __last; ++__cur)
      _Construct(&*__cur, __x);
  }
  __STL_UNWIND(_Destroy(__first, __cur));
}

template <class _ForwardIter, class _Tp, class _Tp1>
inline void __uninitialized_fill(_ForwardIter __first, 
                                 _ForwardIter __last, const _Tp& __x, _Tp1*)
{
  typedef typename __type_traits<_Tp1>::is_POD_type _Is_POD;
  __uninitialized_fill_aux(__first, __last, __x, _Is_POD());
                   
}

template <class _ForwardIter, class _Tp>
inline void uninitialized_fill(_ForwardIter __first,
                               _ForwardIter __last, 
                               const _Tp& __x)
{
  __uninitialized_fill(__first, __last, __x, __VALUE_TYPE(__first));
}


//--------------------------------------------------------------------------------------
// Valid if copy construction is equivalent to assignment, and if the
//  destructor is trivial.
template <class _ForwardIter, class _Size, class _Tp>
inline _ForwardIter
__uninitialized_fill_n_aux(_ForwardIter __first, _Size __n,
                           const _Tp& __x, __true_type)
{
  return fill_n(__first, __n, __x);
}

template <class _ForwardIter, class _Size, class _Tp>
_ForwardIter
__uninitialized_fill_n_aux(_ForwardIter __first, _Size __n,
                           const _Tp& __x, __false_type)
{
  _ForwardIter __cur = __first;
  __STL_TRY {
    for ( ; __n > 0; --__n, ++__cur)
      _Construct(&*__cur, __x);
    return __cur;
  }
  __STL_UNWIND(_Destroy(__first, __cur));
}

template <class _ForwardIter, class _Size, class _Tp, class _Tp1>
inline _ForwardIter 
__uninitialized_fill_n(_ForwardIter __first, _Size __n, const _Tp& __x, _Tp1*)
{
  typedef typename __type_traits<_Tp1>::is_POD_type _Is_POD;
  return __uninitialized_fill_n_aux(__first, __n, __x, _Is_POD());
}

template <class _ForwardIter, class _Size, class _Tp>
inline _ForwardIter 
uninitialized_fill_n(_ForwardIter __first, _Size __n, const _Tp& __x)
{
  return __uninitialized_fill_n(__first, __n, __x, __VALUE_TYPE(__first));
}


//--------------------------------------------------------------------------------------
// Extensions: __uninitialized_copy_copy, __uninitialized_copy_fill, 
// __uninitialized_fill_copy.

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

template <class _InputIter1, class _InputIter2, class _ForwardIter>
inline _ForwardIter
__uninitialized_copy_copy(_InputIter1 __first1, _InputIter1 __last1,
                          _InputIter2 __first2, _InputIter2 __last2,
                          _ForwardIter __result)
{
  _ForwardIter __mid = uninitialized_copy(__first1, __last1, __result);
  __STL_TRY {
    return uninitialized_copy(__first2, __last2, __mid);
  }
  __STL_UNWIND(_Destroy(__result, __mid));
}

// __uninitialized_fill_copy
// Fills [result, mid) with x, and copies [first, last) into
//  [mid, mid + (last - first)).
template <class _ForwardIter, class _Tp, class _InputIter>
inline _ForwardIter 
__uninitialized_fill_copy(_ForwardIter __result, _ForwardIter __mid,
                          const _Tp& __x,
                          _InputIter __first, _InputIter __last)
{
  uninitialized_fill(__result, __mid, __x);
  __STL_TRY {
    return uninitialized_copy(__first, __last, __mid);
  }
  __STL_UNWIND(_Destroy(__result, __mid));
}

// __uninitialized_copy_fill
// Copies [first1, last1) into [first2, first2 + (last1 - first1)), and
//  fills [first2 + (last1 - first1), last2) with x.
template <class _InputIter, class _ForwardIter, class _Tp>
inline void
__uninitialized_copy_fill(_InputIter __first1, _InputIter __last1,
                          _ForwardIter __first2, _ForwardIter __last2,
                          const _Tp& __x)
{
  _ForwardIter __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: