【C++】STL之迭代器介绍、原理、失效

template<typename InputIterator, typename T>
InputIterator find(InputIterator first, InputIterator last, const T &value)
{
    while (first != last && *frist != value)
        ++first;
    return first;
}

 template<typename T,class Alloc = alloc >
    class vector
    { 
 public:
      typedef T    value_type;
      typedef value_type*  iterator;
      ······
 };

#ifndef CPP_PRIMER_MY_LIST_H
#define CPP_PRIMER_MY_LIST_H
#include <iostream>
template<typename T>
class node {
public:
    T value;
    node *next;
    node() : next(nullptr) {}
    node(T val, node *p = nullptr) : value(val), next(p) {}
};

template<typename T>
class my_list {
private:
    node<T> *head;
    node<T> *tail;
    int size;

private:
    class list_iterator {
    private:
        node<T> *ptr; //指向list容器中的某个元素的指针

    public:
        list_iterator(node<T> *p = nullptr) : ptr(p) {}
        
        //重载++、--、*、->等基本操作
        //返回引用，方便通过*it来修改对象
        T &operator*() const {
            return ptr->value;
        }

        node<T> *operator->() const {
            return ptr;
        }

        list_iterator &operator++() {
            ptr = ptr->next;
            return *this;
        }

        list_iterator operator++(int) {
            node<T> *tmp = ptr;
            // this 是指向list_iterator的常量指针，因此*this就是list_iterator对象，前置++已经被重载过
            ++(*this);
            return list_iterator(tmp);
        }

        bool operator==(const list_iterator &t) const {
            return t.ptr == this->ptr;
        }

        bool operator!=(const list_iterator &t) const {
            return t.ptr != this->ptr;
        }
    };

public:
    typedef list_iterator iterator; //类型别名
    my_list() {
        head = nullptr;
        tail = nullptr;
        size = 0;
    }

    //从链表尾部插入元素
    void push_back(const T &value) {
        if (head == nullptr) {
            head = new node<T>(value);
            tail = head;
        } else {
            tail->next = new node<T>(value);
            tail = tail->next;
        }
        size++;
    }

    //打印链表元素
    void print(std::ostream &os = std::cout) const {
        for (node<T> *ptr = head; ptr != tail->next; ptr = ptr->next)
            os << ptr->value << std::endl;
    }

public:
    //操作迭代器的方法
    //返回链表头部指针
    iterator begin() const {
        return list_iterator(head);
    }

    //返回链表尾部指针
    iterator end() const {
        return list_iterator(tail->next);
    }

    //其它成员函数 insert/erase/emplace
};

#endif //CPP_PRIMER_MY_LIST_H

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

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{};