C++ Bidirectional 迭代器

#include <iostream>
#include<iterator>
#include<vector>
using namespace std;
int main()
{
   vector<int> v{1,2,3,4,5};                      //向量声明
   vector<int> ::iterator itr;                       //迭代器声明
   vector<int> ::reverse_iterator ritr;        //反向迭代器声明
   for(itr = v.begin();itr!=v.end();itr++)
   {
       cout<<*itr<<" ";
   }
   cout<<'\n';
   for(ritr = v.rbegin();ritr!= v.rend();ritr++)
   {
       cout<<*ritr<<" ";
   }
    return 0;
}

A==B;
A!=B;

*A = t;
t = *A

A++;
++A;

A--;
--A;

A==B;          //valid
A<=B;          //invalid

A+2;             //invalid
A+1;             //invalid