Public Function my_daily(nowdate As Date) As Integer
Dim my_date_first_day As Date '定义当前月的第一天
Dim my_date_last_day As Date '定义下個月的第一天
Dim my_date_current_day As Integer '定义今天为当前月的第几天
my_date_current_day = Day(nowdate)
my_date_first_day = DateAdd("d", -(my_date_current_day - 1), nowdate)
my_date_last_day = DateAdd("m", 1, my_date_first_day)
my_daily = DateDiff("d", my_date_first_day, my_date_last_day)
End Function

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如:my_daily("2002-2-1") 返回28
my_daily("2002-7-1") 返回31"