不断"Attempting to reference a deleted function"

所以我目前正在尝试制作输出流插入运算符并尝试使其以某种方式显示日期，但我不断收到"尝试引用已删除的函数"错误。我不确定问题可能是什么。有什么帮助吗？

class Date {
private:
static int day;
static int month;
static int year;
public:
static string wordmonth[];
Date(int d, int m, int y) {
this->day = d;
month = m;
year = y;
}
Date(int d) {
this->day = d;
}
Date() {
}
void setDay(int d) {
this->day = d;
}
void setMonth(int m) {
month = m;
}
void setYear(int y) {
year = y;
}
int getDay() {
return day;
}
int getMonth() {
return month;
}
int getYear() {
return year;
}
void print1();
void print2();
void print3();
Date operator ++ () {
day++;
return *this;
}
Date operator ++ (int) {
Date day = *this;
++* this;
return day;
}
Date operator -- () {
day--;
return day;
}
Date operator -- (int) {
--day;
return day;
}
Date operator - (Date v) {
Date temp;
temp.day = day - v.day;
temp.month = month;
temp.year = year;
return temp;
};  

这是我正在尝试工作的操作员。

friend ostream operator << (ostream& output, Date& obj) {
output << wordmonth[month - 1] << " " << day << ". " << year;
return output;
}
};