Var
  DT: TDateTime;
begin
  DT := StartOfTheMonth(Now);
  ShowMessage(DateTimeStr(DT));
end;

Var
  DT: TDateTime;
begin
  DT := EndOfTheMonth(Now);
  ShowMessage(DateTimeToStr(DT));
end;

Var
  DT1, DT2: TDateTime;
begin
  DT1 := StartOfTheMonth(IncMonth(Now, -1));
  ShowMessage(DateTimeToStr(DT1));
  //以上為上月一日的日期
  DT2 := EndOfTheMonth(IncMonth(Now, -1));
  ShowMessage(DateTimeToStr(DT2));
  ////以上為上月最后一日的日期
end;

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