c++ - 迭代器类别

Question

在代码中:

//I know that to get this effect (being able to use it with std algorithms) I can inherit like I did in line below:

    class Iterator //: public std::iterator<std::bidirectional_iterator_tag,T>

    {
    private:
        T** itData_;
    public:
        //BUT I WOULD LIKE TO BE ABLE TO DO IT BY HAND AS WELL
        typedef std::bidirectional_iterator_tag iterator_category;
        typedef T* value_type;//SHOULD IT BE T AS value_type or T*?
        typedef std::ptrdiff_t difference_type;
        typedef T** pointer;//SHOULD IT BE T* AS pointer or T**?
        typedef T*& reference;//SHOULD IT BE T& AS reference or T*&?
};

基本上我要问的是，如果我在迭代器类中有类型为 T** 的变量，是否正确假设此迭代器的值类型将是 T* 等等，正如我在代码注释中所描述的那样，就在下一个到相关行。
谢谢。

Answer 1

标准(第 24.3.2 节)中的定义是:

template<class Category, class T, class Distance = ptrdiff_t,
         class Pointer = T*, class Reference = T&>
struct iterator {
    typedef T value_type;
    typedef Distance difference_type;
    typedef Pointer pointer;
    typedef Reference reference;
    typedef Category iterator_category;
};

如您所见，默认值是:

typedef T value_type;
typedef ptrdiff_t difference_type;
typedef T* pointer;
typedef T& reference;

这是假设迭代是在 T 类型元素的容器上进行的。如果您的容器包含 T* 类型的元素，那么您问题中的 typedef 就是正确的。