C++入门经典-例9.6-有界数组模板，数组下标的越界警告

// 9.6.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <cassert>
using namespace std;

class Date
{
    int iMonth,iDay,iYear;
    char Format[128];
public:
    Date(int m=0,int d=0,int y=0)
    {
        iMonth=m;
        iDay=d;
        iYear=y;
    }
    friend ostream& operator<<(ostream& os,const Date t)
    {
        cout << "Month: " << t.iMonth << ‘ ‘ ;
        cout << "Day: " << t.iDay<< ‘ ‘;
        cout << "Year: " << t.iYear<< ‘ ‘ ;
        return os;
        
    }
    void Display()
    {
        cout << "Month: " << iMonth;
        cout << "Day: " << iDay;
        cout << "Year: " << iYear;
        cout << endl;
    }
};

template <class T,int b>
class Array
{
    T elem[b];
    public:
        Array(){}
        T& operator[] (int sub)
        {
            assert(sub>=0&& sub<b);
            return elem[sub];
        }
        
};
void main()
{
    Array<Date,3> dateArray;
    Date dt1(1,2,3);
    Date dt2(4,5,6);
    Date dt3(7,8,9);
    dateArray[0]=dt1;
    dateArray[1]=dt2;
    dateArray[2]=dt3;
    for(int i=0;i<3;i++)
        cout << dateArray[i] << endl;
    Date dt4(10,11,13);
    dateArray[3] = dt4;                //弹出警告
    cout << dateArray[3] << endl;
}