EXCEL中日期改为显示星期几的自定义涵数

函数DateOfWeek(ByVal Yearf为整数，ByVal Weekf为整数，可选ByVal Dayf为整数= 1，可选ByVal FirstDayOfWeek为整数= 0)
On Error GoTo ext
Dim FD为日期，fw %
FD = DateValue(Yearf & "-1-1 ")
fw = Weekday(FD)
first day ofweek = first day ofweek Mod 7
DateOfWeek =