计算某年的某月有多少天

今天有要求想返回一个月有多少天,在网上找了找,用以下的函数可以实现.




Code
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function DaysInAMonth(const AYear,AMonth:Word):Word; //for Delphi5
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begin
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Result:=MonthDays[(AMonth=2) and IsLeapYear(AYear),AMonth];
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end;
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procedure TForm1.Button1Click(Sender: TObject);
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var
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ss:Word;
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yy,mm,dd:Word;
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begin
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DecodeDate(Now,yy,mm,dd);
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ss:=DaysInAMonth(yy,mm);
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ShowMessage(IntToStr(ss));
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end;

比较可以学习和借鉴的地方是MonthDays 和IsLeapYear函数的实现:




MonthDays
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{ The MonthDays array can be used to quickly find the number of
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days in a month: MonthDays[IsLeapYear(Y), M] }
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const
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MonthDays: array [Boolean] of TDayTable =
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((31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31),
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(31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31));

判断是否为润年:




IsLeapYear
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function IsLeapYear(Year: Word): Boolean;
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begin
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Result := (Year mod 4 = 0) and ((Year mod 100 <> 0) or (Year mod 400 = 0));
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end;
闰年的计算方法：公元纪年的年数可以被四整除，即为闰年；被100整除而不能被400整除为平年；

被100整除也可被400整除的为闰年。如2000年是闰年，而1900年不是。

判断是星期几:




DayOfWeek
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function DayOfWeek(const DateTime: TDateTime): Word;
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begin
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Result := DateTimeToTimeStamp(DateTime).Date mod 7 + 1;
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end;




TimeStamp
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{ Date and time record }
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TTimeStamp = record
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Time: Integer; { Number of milliseconds since midnight }
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Date: Integer; { One plus number of days since 1/1/0001 }
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end;