How to add days and hours to a date-time variable?

2
votes

If I need to get a date like 12/30/2013 and add 10 days at 8pm, How can I do that in Delphi if I have a TDateTime variable with that first date?

3
delphi

3 Answers

8
votes

You can use the + operator to add an integral number of days, and use SysUtils.ReplaceTime() to change the time, eg:

uses
  ..., SysUtils;

var
  DT: TDateTime;
begin
  DT := EncodeDate(2013, 12, 30); // Dec 30 2013 @ 12AM
  DT := DT + 10; // Jan 9 2014 @ 12AM
  ReplaceTime(DT, EncodeTime(20, 0, 0, 0)); // Jan 9 2014 @ 8PM
end;
8
votes

The DateUtils unit has a swath of helpers that allow you to insulate yourself from the way TDateTime is encoded. For instance:

uses
  SysUtils, DateUtils;
....
var
  DT: TDateTime;
....
DT := EncodeDate(2013, 12, 30); // Dec 30 2013 @ 12AM
DT := IncDay(DT, 10);
DT := IncHour(DT, 20);

This is perhaps a little long-winded but I chose that approach to illustrate both IncDay and IncHour. I do recommend studying the contents of DateUtils to familiarise yourself with all of its functionaility.

Another way to do this would be like so:

DT := EncodeDateTime(2013, 12, 30, 20, 0, 0, 0); // Dec 30 2013 @ 8PM
DT := IncDay(DT, 10);

Or even:

DT := IncDay(EncodeDateTime(2013, 12, 30, 20, 0, 0, 0), 10);
0
votes

Here's how to do it:

uses
    SysUtils, DateUtils;
...
procedure TForm1.Button1Click(Sender: TObject);
var
    DT : TDateTime;
begin
    DT := StrToDate('30/12/2013');
    DT := DT + 10;
    ReplaceTime(DT, EncodeTime(20, 0, 0, 0));        
    ShowMessage(DateTimeToStr( DT ));
end;