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Comparing dates in Delphi. Greater than/ Less than

Posted on 2016-07-27
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Last Modified: 2016-07-27
I have a TcxGrid and on a DB column on validate i run the following code.

  
sDate := VarToStr(DisplayValue);
  sNew  := (DateToStr(Now + 49));
  if (sDate < sNew) then begin 
    MessageDlg('Please enter a Committed Delivery Date that is 7 weeks from today.', mtError, [mbOK], 0);
    gvMasterChangeLogCommittedDelivery.DataBinding.Field.Clear;
    gvMasterChangeLog.DataController.DataSet.FieldValues['PlannedInstall']  := sInstall; //INSTALL
    gvMasterChangeLogCommittedDelivery.Focused;
    exit;
  end;

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the problem is that if someone picks a date in the following month (October, greater than September) it still runs the error message.
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Question by:Bianca
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3 Comments
 
LVL 14

Expert Comment

by:SteveBay
ID: 41731533
Why are you comparing them as strings?

It would be more accurate to compare two dates (which are double values) rather than dates that have been converted to strings.

'10' < '9' = True // String comparison
10 < 9 = False // Date (numeric) comparison.
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Author Comment

by:Bianca
ID: 41731569
I'm not sure how to do that. How do i take the selected date and compare it to today + 49 (Seven weeks)?
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LVL 14

Accepted Solution

by:
SteveBay earned 500 total points
ID: 41731631
Assuming that "DisplayValue" is a Variant it would look something like this:
procedure TForm1.Button1Click(Sender: TObject);
var  DisplayValue : Variant;
     dDate, dNew : TDate;
begin
     DisplayValue := DateTimePicker1.DateTime;
     dDate := VarToDateTime(DisplayValue);
     dNew := Now + 49;
     if dDate < dNew then
          ShowMessage('Date is too soon')
     else
          ShowMessage('Date is Acceptable');
end;

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