一个书下的小程序，为什么运行结果却不是现在的时间

一个书上的小程序，为什么运行结果却不是现在的时间？
[code=C/C++][/code]
#include<iostream>
#include<ctime>
#include<stdio.h>

using namespace std;

class Date {
int mo, da, yr;
public:
Date(time_t);
void display();
};

void Date::display()
{
char year[5];
if (yr < 10)
sprintf(year, "0%d", yr);
else
sprintf(year, "%d", yr);
cout << mo << '/' << da <<'/' << year << endl;
}

Date::Date(time_t now)
{
tm* tim = localtime(&now);
da = tim->tm_mday;
mo = tim->tm_mon;
yr = tim->tm_year;
if (yr >= 100)
yr -= 100;
}

int main()
{
time_t now = time(0);
Date dt(now);
dt.display();
return 0;
}

------解决方案--------------------
tm_year：year since 1900
tm_mon: month (0 – 11, 0 = January)
------解决方案--------------------
这是tm结构体的范围
Member Meaning Range 
tm_sec seconds after the minute 0-61 
tm_min minutes after the hour 0-59 
tm_hour hours since midnight 0-23 
tm_mday day of the month 1-31 
tm_mon months since January 0-11 
tm_year years since 1900
tm_wday days since Sunday 0-6 
tm_yday days since January 1 0-365 
tm_isdst Daylight Saving Time flag

月份是0-11， 所以你要+1才是实际的月份
年份是-1900之后的值，现在2012 ，减去1900 112，因为你有个y-=100,所以最后得到12.