TDateTime To ShortDateString In Satellite Forms "VB-clone"

I am trying to find a calculation that will convert the TDateTime value 40653.6830593 into a year, a month, a day, an hour, a minute and a second.

I am sure this is possible, of course, but my brain doesn't 开发者_如何学Chave the power, it seems, to write a formula that will extract those values from that double.

I am using a Satellite Forms, a vb-like language, but don't expect that I would need any specific .NET libraries to do this, right? It should just be a numeric calculation... right?

Thanks for the help! Most sincerely.

Joe

Based on your 'Delphi' tag...

In Delphi

implementation

uses DateUtils;

....    
var
  MyDate: TDateTime;
  ...other vars...
begin
  MyDate:= double(40653.6830593);
  MyYear:= YearOf(MyDate);
  MyMonth:= MonthOf(MyDate);
  MyDay:= DayOf(MyDate);
  MyHour:= HourOf(MyDate);
  MyMinute:= ... ah well you get the idea.

BTW: VB or Delphi, which is it?

If you want to roll your own

From the sysutils unit (released under a dual license GPL2/Borland No nonsense)
Which you can find at: http://www.koders.com/delphi/fidF6715D3FD1D4A92BA7F29F96643D8E9D11C1089F.aspx?s=hook

function DecodeDateFully(const DateTime: TDateTime; var Year, Month, Day, DOW: Word): Boolean;
const
  D1 = 365;
  D4 = D1 * 4 + 1;
  D100 = D4 * 25 - 1;
  D400 = D100 * 4 + 1;
var
  Y, M, D, I: Word;
  T: Integer;
  DayTable: PDayTable;
begin
  T := DateTimeToTimeStamp(DateTime).Date;
  if T <= 0 then
  begin
    Year := 0;
    Month := 0;
    Day := 0;
    DOW := 0;
    Result := False;
  end else
  begin
    DOW := T mod 7 + 1;
    Dec(T);
    Y := 1;
    while T >= D400 do
    begin
      Dec(T, D400);
      Inc(Y, 400);
    end;
    DivMod(T, D100, I, D);
    if I = 4 then
    begin
      Dec(I);
      Inc(D, D100);
    end;
    Inc(Y, I * 100);
    DivMod(D, D4, I, D);
    Inc(Y, I * 4);
    DivMod(D, D1, I, D);
    if I = 4 then
    begin
      Dec(I);
      Inc(D, D1);
    end;
    Inc(Y, I);
    Result := IsLeapYear(Y);
    DayTable := @MonthDays[Result];
    M := 1;
    while True do
    begin
      I := DayTable^[M];
      if D < I then Break;
      Dec(D, I);
      Inc(M);
    end;
    Year := Y;
    Month := M;
    Day := D + 1;
  end;
end;


function IsLeapYear(Year: Word): Boolean;
begin
  Result := (Year mod 4 = 0) and ((Year mod 100 <> 0) or (Year mod 400 = 0));
end;

function TryEncodeDate(Year, Month, Day: Word; out Date: TDateTime): Boolean;
var
  I: Integer;
  DayTable: PDayTable;
begin
  Result := False;
  DayTable := @MonthDays[IsLeapYear(Year)];
  if (Year >= 1) and (Year <= 9999) and (Month >= 1) and (Month <= 12) and
    (Day >= 1) and (Day <= DayTable^[Month]) then
  begin
    for I := 1 to Month - 1 do Inc(Day, DayTable^[I]);
    I := Year - 1;
    Date := I * 365 + I div 4 - I div 100 + I div 400 + Day - DateDelta;
    Result := True;
  end;
end;

Legacy VB or VBA (even Excel) would treat a Date as the number of days since 12/30/1899, and I believe the same is true for Delphi. As such, in legacy VB/VBA, you could write

Dim myDate as Date
myDate = myDate + 40653.68303593

To get April 20, 2011 4:23:36 PM. In VB.NET, it's different, as the DateTime struct defaults to January 1, 0001.

Dim myDate As New DateTime(1899, 12, 30)
myDate = myDate.AddDays(40653.68303593)

Another user has already posted a Delphi answer.

At any rate, the basic premise is that you're adding the number of days, with the decimal portion representing the time. So in this example, 40653 full days have passed since 12/30/1899, and 0.683... partial days.

To extract Hours:

remember 1.0 = 1 day = 24 hours, thus

DayPart:= double(MyDateTime) - Floor(double(MyDateTime));    
//there is a function for fraction, but I forgot the name, 
//never use that stuff. 

//if we want to round 0.9999999999 up from 23:59:59 to 24:00:00, do this:
if (RoundTimeUpByHalfASecond = true) then DayPart:= DayPart + (1/(24*60*60*2));

hours:= floor(DayPart*24);
minutes:= floor(DayPart*24*60) mod 60; 
seconds:= minutes:= floor(DayPart*24*60*60) mod 60;

Hope that helps