vector容器的两种insert方法

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本文解析了C++标准库中vector容器的两种关键插入方法：通过迭代器插入整数或复制元素，以及通过范围插入任意类型的数据。了解这些技巧有助于提升代码效率，但需注意对性能的影响并考虑使用list等替代结构。

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vector容器的两种insert方法：
1: insert(const_iterator pos, int count,element);//迭代器指向位置pos插入count个元素element

#if __cplusplus >= 201103L
      /**
       *  @brief  Inserts a number of copies of given data into the %vector.
       *  @param  __position  A const_iterator into the %vector.
       *  @param  __n  Number of elements to be inserted.
       *  @param  __x  Data to be inserted.
       *  @return  An iterator that points to the inserted data.
       *
       *  This function will insert a specified number of copies of
       *  the given data before the location specified by @a position.
       *
       *  Note that this kind of operation could be expensive for a
       *  %vector and if it is frequently used the user should
       *  consider using std::list.
       */
iterator  insert(const_iterator __position, size_type __n, const value_type& __x)
{
	difference_type __offset = __position - cbegin();
	_M_fill_insert(begin() + __offset, __n, __x);
	return begin() + __offset;
}
#else
      /**
       *  @brief  Inserts a number of copies of given data into the %vector.
       *  @param  __position  An iterator into the %vector.
       *  @param  __n  Number of elements to be inserted.
       *  @param  __x  Data to be inserted.
       *
       *  This function will insert a specified number of copies of
       *  the given data before the location specified by @a position.
       *
       *  Note that this kind of operation could be expensive for a
       *  %vector and if it is frequently used the user should
       *  consider using std::list.
       */
void  insert(iterator __position, size_type __n, const value_type& __x)
{ 
	_M_fill_insert(__position, __n, __x); 
}
#endif

2: insert(const_iterator pos, const char* in,in+len);

#if __cplusplus >= 201103L
      /**
       *  @brief  Inserts a range into the %vector.
       *  @param  __position  A const_iterator into the %vector.
       *  @param  __first  An input iterator.
       *  @param  __last   An input iterator.
       *  @return  An iterator that points to the inserted data.
       *
       *  This function will insert copies of the data in the range
       *  [__first,__last) into the %vector before the location specified
       *  by @a pos.
       *
       *  Note that this kind of operation could be expensive for a
       *  %vector and if it is frequently used the user should
       *  consider using std::list.
       */
template<typename _InputIterator, typename = std::_RequireInputIter<_InputIterator>>
iterator  insert(const_iterator __position, _InputIterator __first, _InputIterator __last)
{
	  difference_type __offset = __position - cbegin();
	  _M_insert_dispatch(begin() + __offset, __first, __last, __false_type());
	  return begin() + __offset;
}
#else
      /**
       *  @brief  Inserts a range into the %vector.
       *  @param  __position  An iterator into the %vector.
       *  @param  __first  An input iterator.
       *  @param  __last   An input iterator.
       *
       *  This function will insert copies of the data in the range
       *  [__first,__last) into the %vector before the location specified
       *  by @a pos.
       *
       *  Note that this kind of operation could be expensive for a
       *  %vector and if it is frequently used the user should
       *  consider using std::list.
       */
template<typename _InputIterator>
void  insert(iterator __position, _InputIterator __first, _InputIterator __last)
{
	  // Check whether it's an integral type.  If so, it's not an iterator.
	  typedef typename std::__is_integer<_InputIterator>::__type _Integral;
	  _M_insert_dispatch(__position, __first, __last, _Integral());
}
#endif