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Delphi 4 : Incrementing the result of 'Now' by a negative amount of minutes

Posted on 2006-11-30
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Last Modified: 2011-09-20
Hello.

I have the below line:

 if (StrToDateTime(QueryNextRun.FieldByName('report_lastrun').AsString) > IncMinute(Now, -180)) then

Which fails to work, as I am using Delphi 4, and I guess IncMinute is in the later versions.

So my question is, how can I achieve the above in Delphi 4?

Just want to compare 2 date/time values, where the 1st comes from a SQL table (Format: dd/mm/yyyy HH:MM:SS) and the second is Now minus about 180 minutes
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Question by:wbstech
8 Comments
 
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Accepted Solution

by:
kretzschmar earned 500 total points
ID: 18044590
use now - 180/1440

meikl ;-)
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Expert Comment

by:wimmeyvaert
ID: 18044624
When calculating with date/time, you have the following rule :
1 exact day = 1 (So Now + 1 = tomorrow).

So :
1 day = 1
--> 1 minute = ( 1 / 24 ) / 60 = 6,9444444444444444444444444444444e-4
--> 180 minutes = 6,9444444444444444444444444444444e-4 * 180 = 0,125


In a Delphi Example :

var
  aDate: TDateTime;

  aDate := Now;
  showmessage( FormatDateTime( 'dd/mm/yyyy hh:nn:ss:zzz', aDate ) +
               #13#10 +
               FormatDateTime( 'dd/mm/yyyy hh:nn:ss:zzz', aDate-StrToFloat(Edit5.Text) ) );


This shows you exactly the current date/time and current date/time minus 180 minutes.

So, instead of IncMinute(Now, -180) you can use (Now-0.125)

Best regards,

The Mayor.
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Expert Comment

by:wimmeyvaert
ID: 18044639
damn, too slow again ! ;-)
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LVL 6

Expert Comment

by:wimmeyvaert
ID: 18044649
Btw, I found IncMinute in the DateUtil-Unit of the RxLib !

Didn't know about that function.

So, if you have RxLib installed, it is enough to include the DateUtil in your uses-clause.
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LVL 6

Expert Comment

by:wimmeyvaert
ID: 18044687
In this unit DateUtil.pas there is :

function IncMinute(ATime: TDateTime; Delta: Integer): TDateTime;
begin
  Result := IncTime(ATime, 0, Delta, 0, 0);
end;


and of course also :

function IncTime(ATime: TDateTime; Hours, Minutes, Seconds,
  MSecs: Integer): TDateTime;
begin
  Result := ATime + (Hours div 24) + (((Hours mod 24) * 3600000 +
    Minutes * 60000 + Seconds * 1000 + MSecs) / MSecsPerDay);
  if Result < 0 then Result := Result + 1;
end;

the variable MSecsPerDay = 24 * 60 * 60 * 1000
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LVL 6

Expert Comment

by:wimmeyvaert
ID: 18044761
Or you can make you own IncMinute-Function Like this :

function IncMinute( ATime: TDateTime; Delta: Integer ): TDateTime;
begin
  Result := aDate + ( ( ( 1 / 24 ) / 60) * Delta );
end;
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LVL 45

Expert Comment

by:aikimark
ID: 18044851
reference for future readers:
NOW (Windows timestamp) is a floating point numeric value with the integer value being the number of days since 1899-12-31 (yyyy-mm-dd format) and the decimal value being a percentage of the date (starting at midnight).

There fractional part of the day is usually displayed down to a one second granularity, but it is accurate down to 1/100 second.

To avoid unnecessary divisions, remember these conversion constants:
86400 - seconds in a day
1440 - minutes in a day
24 - hours in a day (duh)

==================================
If you need a more granular or more reliable timestamp, you would avoid NOW and use a Multi-Media timing value or a Tick timing value.
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LVL 4

Author Comment

by:wbstech
ID: 18053589
Thanks for the massive amount of detail folks. Didn't expect all that! :-)
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