详解C++ 的STL迭代器原理和实现

//
// Created by wengle on 2020-03-14.
//
 
#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

//// Created by wengle on 2020-03-14.//#include <string>#include "my_list.h"struct student {    std::string name;    int age;    student(std::string n, int a) : name(n), age(a) {}    //重载输出操作符    friend std::ostream &operator<<(std::ostream &os, const student &stu) {        os << stu.name << " " << stu.age;        return os;    }};int main() {    my_list<student> l;    l.push_back(student("bob", 1)); //临时量作为实参传递给push_back方法    l.push_back(student("allen", 2));    l.push_back(student("anna", 3));    l.print();    for (my_list<student>::iterator it = l.begin(); it != l.end(); it++) {        std::cout << *it << std::endl;        *it = student("wengle", 18);    }    return 0;}//
// Created by wengle on 2020-03-14.
//
 
#include <string>
#include "my_list.h"
 
struct student {
    std::string name;
    int age;
 
    student(std::string n, int a) : name(n), age(a) {}
 
    //重载输出操作符
    friend std::ostream &operator<<(std::ostream &os, const student &stu) {
        os << stu.name << " " << stu.age;
        return os;
    }
};
 
int main() {
    my_list<student> l;
    l.push_back(student("bob", 1)); //临时量作为实参传递给push_back方法
    l.push_back(student("allen", 2));
    l.push_back(student("anna", 3));
    l.print();
 
    for (my_list<student>::iterator it = l.begin(); it != l.end(); it++) {
        std::cout << *it << std::endl;
        *it = student("wengle", 18);
    }
    return 0;
}

// inserting into a vector
#include <iostream>
#include <vector>
 
int main ()
{
  std::vector<int> myvector (3,100);
  std::vector<int>::iterator it;
 
  it = myvector.begin();
  it = myvector.insert ( it , 200 );
 
  myvector.insert (it,200,300);
  //it = myvector.insert (it,200,300);
  myvector.insert (it,5,500); //当程序执行到这里时，大概率会crash
  for (std::vector<int>::iterator it2=myvector.begin(); it2<myvector.end(); it2++)
    std::cout << ' ' << *it2;
  std::cout << '\n';
 
  return 0;
}