istream 运算符重载 C++

我正在尝试做一个简单的 istream 运算符重载，但是由于某种原因，一旦进入这个函数，程序就会进入无限循环.请帮忙！

i'm trying to do a simple istream operator overloading, but for some reason, once entering this function, the program enters an infinite loop. please help!

我的代码:

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

 class date{

int m_day,m_month,m_year;

public:

date(int day=1,int month=1,int year=2000){    //constructor
    if (day>0 && day<32 && month>0 && month<13){
        m_day =day;
        m_month=month;
        m_year=year;
    }
}


friend ostream& operator<< (ostream& out, const date& d);
friend istream& operator>> (istream& in, const date& d);
};


istream& operator>> (istream& stream, const date& d){              //overload >>
stream >> d.m_day;
return stream;

}

void main(){  

date date1;

cin>>date1;                   //check istream

getchar();
}