[讨论]看下这段程序中类里的红色代码的意义是什么?

#include <iostream>
#include <cstdlib>
#include "File1.h"
using namespace std;

class CDateinfo
{
public:
CDateinfo();
CDateinfo(int year, int month, int day);
~CDateinfo();
void SetDate(int year, int month, int day);
void GetDate();
private:
int year;
int month;
int day;
};

CDateinfo::CDateinfo()
{
this->year = 2007;
this->month = 5;
this->day = 23;
}

CDateinfo::CDateinfo(int year, int month, int day)
{
this->year = year;
this->month = month;
this->day = day;
}

CDateinfo::~CDateinfo()
{
cout << "Unload me" << endl;
this->year = 0;
this->month = 0;
this->day = 0;
}

void CDateinfo::SetDate(int year, int month, int day)
{
this->year = year;
this->month = month;
this->day = day;
}

void CDateinfo::GetDate()
{
cout << "当前日期为: " << this->year << "年"
<< this->month << "月"
<< this->day << "日"
<<endl;
}

int main()
{
CDateinfo* MyDate = new CDateinfo;
MyDate->GetDate();
cout << "执行delete后自动调用析构函数" << endl;
delete MyDate;

cout << endl << endl;

CDateinfo* ThisDate = new CDateinfo(2007, 5, 23);
ThisDate->GetDate();
delete ThisDate;

cout << endl <<endl;

CDateinfo* OtherDate = new CDateinfo;
OtherDate->SetDate(2008,8,8);
OtherDate->GetDate();
delete OtherDate;

cout << endl << endl;

cout << "注意delete OtherDate 后再次调用 OtherDate 的GetDate方法" << endl;
OtherDate->GetDate();

system("pause");
return 0;
}
//---------------------------------------------------------------------------