Summary

STL traits

STL traits的实现

traits 是一种能获取出你所需类型特性的方法：

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struct input_iterator_tag{};
struct output_iterator_tag{};
struct forward_iterator_tag :public input_iterator_tag{};
struct bidirectional_iterator_tag: public forward_iterator_tag{};
struct random_access_iterator_tag: public bidirectional_iterator_tag{};

template<class _Cat,class _T,class _Dis = int,
         class _P = _T*, class _Ref = _T&>
struct iterator
{
	typedef _Cat iterator_category;
	typedef _T   value_type;
	typedef _Dis difference_type;
	typedef _P   pointer;
	typedef _Ref reference;
};

template<class Iterator>
struct iterator_traits
{
	typedef typename Iterator::iterator_category iterator_category;
	typedef typename Iterator::value_type         value_type;
	typedef typename Iterator::difference_type    difference_type;
	typedef typename Iterator::pointer            pointer;
	typedef typename Iterator::reference          reference;
};

template<class T>
struct iterator_traits<T*>
{
	typedef random_access_iterator_tag iterator_category;
	typedef T         value_type;
	typedef int       difference_type;
	typedef T *       pointer;
	typedef T &       reference;
};
template<class T>
struct iterator_traits<const T*>
{
	typedef random_access_iterator_tag iterator_category;
	typedef T               value_type;
	typedef int             difference_type;
	typedef const T *       pointer;
	typedef const T &       reference;
};
template<class Iterator>
typename iterator_traits<Iterator>::iterator_category
iterator_category(Iterator &)			      //迭代器的'类型'
{
	typedef typename iterator_traits<Iterator>::iterator_category iterator_category;
	return iterator_category();
}
template<class Iterator>
typename iterator_traits<Iterator>::value_type*
value_type(Iterator &)                       //迭代器所指之物类型
{
  return static_cast<typename iterator_traits<Iterator>::value_type*>(0);
}

template<class Iterator>
typename iterator_traits<Iterator>::difference_type *
difference_type(Iterator &)                 //获取差值类型
{
	return static_cast<typename iterator_traits<Iterator>::difference_type*>(0);
}

迭代器分类

stl_iterator

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struct input_iterator_tag{};
struct output_iterator_tag{};
struct forward_iterator_tag :public input_iterator_tag{};
struct bidirectional_iterator_tag: public forward_iterator_tag{};
struct random_access_iterator_tag: public bidirectional_iterator_tag{};

advance例子

stl_traits