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Delphi 獲取週期邊界：StartOf/EndOf 系列函數詳解

編輯：Delphi

日期時間週期起止點：年/月/周/日兩組 API（參數類型不同）

DateUtils 提供兩組函數：StartOfAxxx/EndOfAxxx 接收數值參數（年、月、周序數、日序數）；StartOfTheXxx/EndOfTheXxx 接收 TDateTime 參數。返回對應週期的起始/結束瞬間（含毫秒）。

函數對照表

數值參數版	TDateTime 參數版	含義
StartOfAYear(Year)	StartOfTheYear(DateTime)	年初 0:0:0.000
EndOfAYear(Year)	EndOfTheYear(DateTime)	年終 23:59:59.999
StartOfAMonth(Year, Month)	StartOfTheMonth(DateTime)	月初 0:0:0.000
EndOfAMonth(Year, Month)	EndOfTheMonth(DateTime)	月末 23:59:59.999
StartOfAWeek(Year, WeekOfYear)	StartOfTheWeek(DateTime)	周一 0:0:0.000
EndOfAWeek(Year, WeekOfYear)	EndOfTheWeek(DateTime)	周日 23:59:59.999
StartOfADay(Year, DayOfYear)	StartOfTheDay(DateTime)	當日 0:0:0.000
EndOfADay(Year, DayOfYear)	EndOfTheDay(DateTime)	當日 23:59:59.999

測試代碼 (基準時間 2009-5-20 11:22:33)

uses DateUtils;
procedure TForm1.FormCreate(Sender: TObject);
var dt, t1, t2, t3, t4: TDateTime; s1, s2, s3, s4: string;
begin
  dt := StrToDateTime('2009-5-20 11:22:33');

  {年}
  t1 := StartOfAYear(2009);  t2 := StartOfTheYear(dt);
  t3 := EndOfAYear(2009);    t4 := EndOfTheYear(dt);
  {結果: 2009-1-1 0:0:0.000 / 2009-12-31 23:59:59.999}

  {月}
  t1 := StartOfAMonth(2009, 5);  t2 := StartOfTheMonth(dt);
  t3 := EndOfAMonth(2009, 5);    t4 := EndOfTheMonth(dt);
  {結果: 2009-5-1 0:0:0.000 / 2009-5-31 23:59:59.999}

  {周}
  t1 := StartOfAWeek(2009, 21);  t2 := StartOfTheWeek(dt);
  t3 := EndOfAWeek(2009, 21);    t4 := EndOfTheWeek(dt);
  {結果: 2009-5-18 0:0:0.000 / 2009-5-24 23:59:59.999}

  {日}
  t1 := StartOfADay(2009, 140);  t2 := StartOfTheDay(dt);
  t3 := EndOfADay(2009, 140);    t4 := EndOfTheDay(dt);
  {結果: 2009-5-20 0:0:0.000 / 2009-5-20 23:59:59.999}
end;

應用： 報表時間範圍查詢（本月/本周/今日）、定時任務執行窗口判斷、日曆 UI 邊界計算。