关于 二维的vector push_back怎么用？

                                          关于 二维的vector    push_back怎么用？

    //向其中添加数据
    vector<vector<int>> vv;//二维vector
    vector<int> vn;//创建一个一维vector
    vn.push_back(1);
    vn.push_back(2);
    vv.push_back(vn);//将一维vector push进去

    vn.clear();
    vn.push_back(3);
    vn.push_back(4);
    vn.push_back(5);
    vv.push_back(vn);

    //读取其中的数据
    vector<int> vn2;
    for (vector<vector<int>>::iterator it = vv.begin(); it != vv.end(); it++)
    {
        for (vector<int>::iterator it1 = it->begin(); it1 != it->end(); it1++)
        {
            vn2.push_back(*it1);
        }
    } 

头文件为#include
using namespace std;

声明为 vectorv;

int i=0;

v.push_back(i);

这样0就被插入vector尾部

type struct {
char a[5][5];
}TYPE;

TYPE t;

vector < TYPE >v;

v.push _ back(t);

 #include<iostream>
#include<vector>
using namespace std;

typedef struct point
{
    int x;
    int y;
}POINT;

int main()
{
    vector<vector<POINT>> a;
    for(int i = 0; i < 5; i++)
    {
        vector<POINT> b;
        a.push_back(b);
        for(int j = 0; j < 4; j++)
        {
            POINT c = {i, j};
            a[i].push_back(c);
        }
    }

  //用迭代器遍历打印
    vector<vector<POINT>>::iterator vec_it;
    for(vec_it = a.begin(); vec_it != a.end(); vec_it++)
    {
        vector<POINT>::iterator it;
        for(it = (*vec_it).begin(); it != (*vec_it).end(); it++)
        {
            cout << " [" <<it->x << "," << it->y << "] ";
        }
        cout << endl;
    }
    system("pause");
}

vector > xxxxx