vector空间重新配置后指向原vector的所有迭代器失效

对于下面这段话的理解，来自《STL源码剖析》第四章：

#include <vector>

#include <iostream>

using namespace std;

void main()

{

     vector<int> ivec(2,9);

     cout<<"size="<<ivec.size()<<endl;

     cout<<"capacity="<<ivec.capacity()<<endl;

     vector<int>::iterator beg = ivec.begin();

     vector<int>::iterator end = ivec.end();

     cout<<"begin="<<*beg<<endl;

     cout<<"end="<<*(end-1)<<endl;

     //空间重新配置，指向原vector的所有迭代器失效

     ivec.push_back(1);//引起空间重新配置

     cout<<"size="<<ivec.size()<<endl;

     cout<<"capacity="<<ivec.capacity()<<endl;

     cout<<"begin="<<*beg<<endl;//指向原vector的所有迭代器失效

     cout<<"end="<<*(end-1)<<endl;//指向原vector的所有迭代器失效

}