Date / Time

Date conversion - adding century
Days between two dates
Set system date and time (of the computer) using Delphi
Number of current week
How to reset a Timer halfway thru
Convert date to number in milliseconds
Difference between two dates
Time problems
EncodeDate
Time difference
Date Math
Time Variable
Date Conversion
Calcutation of Easter
Dates and weeks
Converting date to week
Adding time and date stamp to memos

Date conversion - adding century

Question

I have to convert a Date from the format 'DD/MM/YY' to 'DDMMYYYY'

Answer

A:

LongDate := FormatDateTime('ddmmyyyy', StrToDate(ShortDate));



This converts a date held in the format specified in the

Control Panel's short date format (which could well be

DD/MM/YY) to the format specified in the Format string

(in the example DDMMYYYY).



If the DD/MM/YY is an input field, and DDMMYYYY is

a database field, it might clever to use code like this as

it should still work correctly for a user who wants to use

a different date format, and accordingly specifies this in

his/her Control Panel.



(Of course YYYYMMDD would normally be better than

DDMMYYYY as a database field because it would be

easier to sort records to date sequence.

Days between two dates

Question

I have two dates and want to know how many days separate them.

Answer

A:

VARIABLES:

    Year1, Month1, Day1,

    Year2, Month2, Day2,

    YearResult, MonthResult, DayResult: Word;

    TDay1, TDay2, DateDiff: TDateTime;

CODE:

    TDay1 := EncodeDate(Year1, Month1, Day1);

    TDay2 := EncodeDate(Year2, Month2, Day2);

    DateDiff := TDay2 - TDay1; {assuming TDay2 is later than TDay1}

    DecodeDate(DateDiff, YearResult, MonthResult, DayResult);



DateDiff actually is a LongInt (albeit a TDateTime object) representing the

difference in days.

Set system date and time (of the computer) using Delphi

Question

I would like know how it's possible set system date and time (of the computer)

using Delphi.

Answer

A:

Yes you can. Use this code:



Procedure settime(hour, min, sec, hundreths : byte); assembler;

asm

     mov  ch, hour

     mov  cl, min

     mov  dh, sec

     mov  dl, hundreths

     mov  ah, $2d

     int  $21

     end;





Procedure setdate(Year : word; Month, Day : byte); assembler;

asm

     mov  cx, year

     mov  dh, month

     mov  dl, day

     mov  ah, $2b

     int  $21

     end;

Number of current week

Question

I need to calculate the week number - does anyone know of a debugged formula

to do this?

Answer

A:

There are 2 other functions included which are required for our

function. One checks for a Leap year, the other returns the # of days

in a month (checking the leap year) and the 3rd is the one you want,

the week of the year.



{***************************************************************************}

function kcIsLeapYear( nYear: Integer ): Boolean;

begin

  Result := (nYear mod 4 = 0) and ((nYear mod 100 <> 0) or (nYear mod

400 = 0));

end;



{***************************************************************************}

function kcMonthDays( nMonth, nYear: Integer ): Integer;

const

  DaysPerMonth: array[1..12] of Integer = (31, 28, 31, 30, 31, 30, 31,

31, 30, 31, 30, 31);

begin

  Result := DaysPerMonth[nMonth];

  if (nMonth = 2) and kcIsLeapYear(nYear) then Inc(Result);

end;



{***************************************************************************}

function kcWeekOfYear( dDate: TDateTime ): Integer;

var

 X, nDayCount: Integer;

 nMonth, nDay, nYear: Word;

begin



  nDayCount := 0;



  deCodeDate( dDate, nYear, nMonth, nDay );



  For X := 1 to ( nMonth - 1 ) do

    nDayCount := nDayCount + kcMonthDays( X, nYear );



  nDayCount := nDayCount + nDay;



  Result := ( ( nDayCount div 7 ) + 1 );



end;

How to reset a Timer halfway thru

Question

My timer is set to 5000 (5 seconds), halfway, thru' this, an event occurs

and I need to reset this Timer back to time zero again...

Answer

A:

Timer1.Enabled := False;

Timer1.Enabled := True;



This will reset the timer for its full duration.



BTW, changing the interval (to a different value) also resets the

timer.



A:

You may enable or disable your timer component, setting its

property, like this:



  Timer1.Enabled := True; { or False, if you want to disable it }



But it will still continue with its 5 secs. If you want to change this,

set another property, the interval one, like this:



  Timer1.Interval := 100;

Convert date to number in milliseconds

Question

PDOXWin allows conversion of a dateTime to a number in milliseconds. Am

trying to write code in Delphi to do the same procedure. I have done the

following which results in date format:



procedure TForm1.Table1NewRecord(DataSet: TDataset);

begin

   Table1.FieldByName('MyField').AsDateTime :=

     EncodeDate(9999, 12, 31) - Now;

end;



Anyone suggest how the code should read if 'MyField' were a number field

and AsDateTime were to change to AsInteger?



How would I get a number that is in milliseconds?

Answer

A:

EncodeDate returns a TDateTime object, which is just a double. To get the

milliseconds since 1/1/0001 multiply the result by 86400000.0 Better yet, first

substract from a more recent base date, so as not to cause overflow.

Difference between two dates

Question

Anybody know where I can get hold of some functions for date manipulation?

I need something like the DateDiff() function in VB that returns the

number of months between dates.

Also, how about a function to calculate Present Value for a string of cash

flows?

Answer

A:

For DateDiff:



Have you looked at the DecodeDate function? It's not exactly the same, but

with it you may be able to get the result by creating your own custom function.



For Present Value



function PresentValue(const cashflows : array of double;    { the cash flows

in consecutive order nearest is at cashflows[0] }

          n : integer; { number of cash flows in array }

          rate : double; { the percent rate per period }

          atbegin : boolean) : double; { true if cash flow at beginning of

          period, false if at end }



var

     i         : integer;

     factor    : double;

begin

     factor := (1 + rate / 100.0);

     result := 0;

     for i := n - 1 downto 0 do

          result := (result + cashflows[n]) / factor;

     if atbegin then

          result := result * factor;

     end;

Time problems

Question

Just tried to use the 'typed constant Time24Hour' as shown in the

EncodeTime function. Can't seem to find this constant in SysUtils or

anywhere else.

Answer

A:

I found Time24Hour in the Help system, as you indicated. But...



here is the code for EncodeTime in SysUtils.Pas file:



function DoEncodeTime(Hour, Min, Sec, MSec: Word; var Time: TDateTime): Boolean;

begin

  Result := False;

  if (Hour < 24) and (Min < 60) and (Sec < 60) and (MSec < 1000) then

  begin

    Time := (LongMul(Hour * 60 + Min, 60000) + Sec * 1000 + MSec) / MSecsPerDay;

    Result := True;

  end;

end;



function EncodeTime(Hour, Min, Sec, MSec: Word): TDateTime;

begin

  if not DoEncodeTime(Hour, Min, Sec, MSec, Result) then

    ConvertError(LoadStr(STimeEncodeError));

end;



As you can see, any Time24Hour check is present. I looked it in the Browser

too. Nothing!



So, I thing is better conclude that Time24Hour is an old intention of

Borland-staff, aborted in Code but not in Help files. Does't you think so?

EncodeDate

Question

Could anyone give me the syntax for converting text to and

from a Paradox Date field value? EncodeDate(xx,xx,xx)?

Answer

TheDateField.AsString := TheDateString;

TheDateString := TheDateField.AsString;



this will do a convert just like DateToStr and StrToDate.  Similar to



TheDateField.AsDateTime := StrToDate(TheDateString);

TheDateString := DateToStr(TheDateField.AsDateTime);

Time difference

Question

var

  TimeStart : TDateTime;

  

procedure TimeTaken;

var

 tt : Double; {Have tried this as TDateTime}

begin

   tt := Now - TimeStart;

   Edit1.Text := FloatToStr(tt);

end;



OK, now matter what I do tt = Now  not the difference. What am I missing.

Answer

A:

I don't know when you execute TimeTaken.. Did you give some delayed time before

executing TimeTaken after execute SetTimeStart? If didn't then no wonder it

tt=Now..

I've tried your code, with some minor changes... and I always got the difference

between Now and TimeStart. But, I declare tt as TDateTime not as Double and

using OnTimer event to execute TimeTaken procs.

You can check it by trying the example below.



{*******************************************************************

 FILE : TIMEEX.PAS

 NOTE : Create form which contains 1 TTimer, and 6 TLabel.

        Set OnTimer Event of TTimer to TForm.Timer1.Timer

 ********************************************************************}

unit Time;



interface



uses

  SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,

  Forms, Dialogs, ExtCtrls, StdCtrls;



type

  TForm1 = class(TForm)

    Timer1: TTimer;

    Label1: TLabel;           {Caption : 'Start :'}

    Label2: TLabel;           

    Label3: TLabel;           {Caption : 'Time : '}

    Label4: TLabel;

    Label5: TLabel;           {Caption : 'Elapsed time:'}

    Label6: TLabel;

    procedure FormCreate(Sender: TObject);

    procedure Timer1Timer(Sender: TObject);

  private

    { Private declarations }

    TimeStart : TDateTime;

  public

    { Public declarations }

  end;



var

  Form1: TForm1;



implementation



{$R *.DFM}



procedure TForm1.FormCreate(Sender: TObject);

begin

 TimeStart := Now;

 Label2.Caption := TimeToStr(Now);

end;



procedure TForm1.Timer1Timer(Sender: TObject); 

var

 tt : TDateTime;

begin

 Label4.Caption := TimeToStr(Now);

 tt:= Now - TimeStart;

 Label6.Caption:= TimeToStr(tt);

end;



end.

Date Math

Question

Is there a function that will do simple date addition or will I have to

write a routine for it?

Answer

A:

procedure TForm1.MaskEdit1Exit(Sender: TObject);

var

  y, m, d : word;

begin

  decodedate(strtodate(maskedit1.text) +  11, y, m, d);

  maskedit2.text := inttostr(m) + '/' + inttostr(d) + '/' + inttostr(y);

end;

Time Variable

Question

How can I keep the elapsed time for a certain process?

For Example:  Beginning Time:  10:45:34, Current Time: 10:48:39

                      Elapsed Time = 00:03:05

Answer

Use variables of type TDateTime.



procedure TForm1.XXXXXXXClick(Sender: TObject);

var StartTime, EndTime, ElapsedTime :TDateTime;

begin

  StartTime := Now;

  {Put your code here}

  EndTime := Now;

  ElapsedTime := EndTime - StartTime;

  Label1.Caption := TimeToStr(ElapsedTime);

end;



A:

{now this is from memory, but it should be a good place to start. }

var

  before,

  after,

  elapsed : TDateTime;

  Ehour, Emin, Esec, Emsec : WORD;

...



before := now;



some_process();



after := now;

elapsed := after - before;



decodetime(elapsed, Ehour, Emin, Esec, Emsec);



now Ehour:Emin:Esec.Emsec will hold the elapsed time {give or take a little;).



A:

This is what I do. fStartWhen hold the date/time when the

process was started. (fStartWhen := NOW). OneSecond is

a constant defined as 1/24/3600. (Yes, this program can

run for days. Even a fast P5 can get overwhelmed with

too much data!)



PROCEDURE	TformDBLoad.UpdateTime;

VAR	Delta	:TDateTime

;

BEGIN

;	fLastUpdate := NOW

;	IF ABS( fStartWhen - fLastUpdate ) < OneSecond THEN EXIT

;	Delta := fLastUpdate - fStartWhen

;	doElapsedTime.Caption := FORMAT( '%1.0f days %s',

[INT(Delta),FORMATDATETIME('hh:nn:ss', FRAC(Delta))] )

END;

Date Conversion

Question

I may be brain dead here but I'm having trouble finding a simple way to

convert a date string given to me like this '1996-06-03 00.00.00'  in to a

string of the format indecated by the Date/Time Formatting Variable:

ShortDateFormat.

Answer

procedure TForm1.Button1Click(Sender: TObject);

var

  st,

  formatsave : string;

  DT         : TDateTime;

begin

  st := Edit1.text; // '1996-06-03 00.00.00'

  formatsave := ShortDateFormat;

  ShortDateFormat := 'yyyy.mm.dd hh.mm.ss';

  while pos ('-', st) > 0 do

    st [pos ('-', st)] := '.';

  DT := StrToDateTime (st);

  ShortDateFormat := formatsave;

  Label1.Caption := DateTimeToStr (DT);

end;

Calcutation of Easter

Question

I've to calculate easter in a project. I found some old

pascal code from years back. I tried to use it, and it

works ok for this year but not for next year (1997).

Answer

 function Easter (Year: Integer): TDateTime;

{----------------------------------------------------------------}

{ Calculates and returns Easter Day for specified year.          }

{ Originally from Mark Lussier, AppVision .   }

{ Corrected to prevent integer overflow if it is inadvertently   }

{ passed a year of 6554 or greater.                              }

{----------------------------------------------------------------}

 var

   nMonth, nDay, nMoon, nEpact, nSunday,

   nGold, nCent, nCorx, nCorz: Integer;

 begin

 { The Golden Number of the year in the 19 year Metonic Cycle: }

   nGold := (Year mod 19) + 1;

 { Calculate the Century: }

   nCent := (Year div 100) + 1;

 { Number of years in which leap year was dropped in order... }

 { to keep in step with the sun: }

   nCorx := (3 * nCent) div 4 - 12;

 { Special correction to syncronize Easter with moon's orbit: }

   nCorz := (8 * nCent + 5) div 25 - 5;

 { Find Sunday: }

   nSunday := (Longint(5) * Year) div 4 - nCorx - 10;

                { ^ To prevent overflow at year 6554}

 { Set Epact - specifies occurrence of full moon: }

   nEpact := (11 * nGold + 20 + nCorz - nCorx) mod 30;

   if nEpact < 0 then

     nEpact := nEpact + 30;

   if ((nEpact = 25) and (nGold > 11)) or (nEpact = 24) then

     nEpact := nEpact + 1;

 { Find Full Moon: }

   nMoon := 44 - nEpact;

   if nMoon < 21 then

     nMoon := nMoon + 30;

 { Advance to Sunday: }

   nMoon := nMoon + 7 - ((nSunday + nMoon) mod 7);

   if nMoon > 31 then

   begin

     nMonth := 4;

     nDay   := nMoon - 31;

   end

   else

   begin

     nMonth := 3;

     nDay   := nMoon;

   end;

   Easter := EncodeDate(Year, nMonth, nDay);

 end; {Easter}

Dates and weeks

Question

Id like to retrieve a week number (1-52) from a date as "1996-06-25".

also I'd like to set a week and a year and get the matching dates for the

at week.

Answer

I have a program that makes something near what you want. It tells which

week is the date of, and the corresponding day of the week. You will have

to implement the calculation of the week limit dates. Besides, the date

format it handles is "06/25/1996".



You have to create form named "Forma", with an TEdit named "Edit1",

four labels, and un button named "GetWeekBtn". You must make sure

that the event OnCreate of the form is set to FormCreate.



I hope it is useful for you, any comments will be welcome.



unit Forma;



interface



uses

  SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,

  Forms, Dialogs, StdCtrls;



type

  TForma1 = class(TForm)

    Edit1: TEdit;

    Label1: TLabel;

    Label2: TLabel;

    Label3: TLabel;

    GetWeekBtn: TButton;

    Label4: TLabel;

    procedure GetWeekBtnClick(Sender: TObject);

    procedure FormCreate(Sender: TObject);

  private

    { Private declarations }

    Function HowManyDays(pYear,pMonth,pDay:word):integer;

  public

    { Public declarations }

  end;

var

  Forma1: TForma1;



implementation



{$R *.DFM}

Uses Inifiles;



procedure TForma1.FormCreate(Sender: TObject);

var       WinIni:TInifile;

begin

     WinIni:=TIniFile.Create('WIN.INI');

     WinIni.WriteString('intl','sShortDate','MM/dd/yyyy');

     WinIni.Free;

end;



Function TForma1.HowManyDays(pYear,pMonth,pDay:word):integer;

var      Sum:integer;

         pYearAux:word;

begin

     Sum:=0;

     if pMonth>1  then Sum:=Sum+31;

     if pMonth>2  then Sum:=Sum+28;

     if pMonth>3  then Sum:=Sum+31;

     if pMonth>4  then Sum:=Sum+30;

     if pMonth>5  then Sum:=Sum+31;

     if pMonth>6  then Sum:=Sum+30;

     if pMonth>7  then Sum:=Sum+31;

     if pMonth>8  then Sum:=Sum+31;

     if pMonth>9  then Sum:=Sum+30;

     if pMonth>10 then Sum:=Sum+31;

     if pMonth>11 then Sum:=Sum+30;



     Sum:=Sum + pDay;

     if ((pYear - (pYear div 4)*4)=3D0) and

        (pMonth>2)then

          inc(Sum);



     HowManyDays:=Sum;

end;   { HowManyDays }



procedure TForma1.GetWeekBtnClick(Sender: TObject);

var

  ADate: TDateTime;

  EditAux:String;

  Week,year,month,day:Word;

begin

  EditAux:=Edit1.Text;

  ADate := StrToDate(EditAux);

  Label1.Caption := DateToStr(ADate);

  DecodeDate(Adate,Year,Month,Day);



  Case DayOfWeek(ADate) of

  1: Label4.Caption:='Sunday';

  2: Label4.Caption:='Monday';

  3: Label4.Caption:='Tuesday';

  4: Label4.Caption:='Wednesday';

  5: Label4.Caption:='Thursday';

  6: Label4.Caption:='Friday';

  7: Label4.Caption:='Saturday';

  end

  Week:=(HowManyDays(year,month,day) div 7) +1;



  Label3.Caption:='Week No. '+IntToStr(Week);

end;



end.

Converting date to week

Question

I need to be able to tell which week number a given date will fall in for

the future, including leap year conversions.

Answer

procedure TForm1.Button1Click(Sender: TObject);

var  frstDay,toDay : TDateTime;  week : Integer;

begin

   frstDay := StrToDate('1/1/96');

   toDay := StrToDate(Edit1.Text);

   week := Trunc((toDay - frstDay) / 7) + 1;

   Label1.Caption := IntToStr(week);

end;

Adding time and date stamp to memos

Question

How to add time and date stamp to memos?

Answer

{ The following code inserts a date/time stamp into a memo field. }



Var     

        s : string ;

begin 

        s :=  DateToStr( Date ) + ' ' + TimeToStr( Time ) + '  :' ;

        Memo1.Lines.Insert( 0,  s ) ;

        Memo1.SetFocus ;

        Memo1.SelStart := Length( s ) ;

        Memo1.SelLength := 0 ;