Solved

I need to compare dates (2)

Posted on 2007-11-30
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Last Modified: 2010-04-21
Hi all,

I need an example code please:

I've got 2 dates in this format: Fri, 30 Nov 2007

I need to compare:

Fri, 30 Nov 2007 with Wed, 29 Aug 2007 for example...

And be able to compare if a date is older than today of 2 days ago.

I'll give full points for an example code please!

Hope you can help...

Thanks

ST3VO
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Question by:ST3VO
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17 Comments
 
LVL 18

Expert Comment

by:Johnjces
Comment Utility
I do not understand;

"...than today of 2 days ago?"

Can you explain what this means?

Do you want to subtract two days from 'today' and compare that with the one or both of the dates?

Thx.

John
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Author Comment

by:ST3VO
Comment Utility
Right....

Everyday, I need to compare a list of images (last Modified) with another...so I only keep the need ones.

Last modified today on weekday!

So, on instance 1 Monday to Friday ....I run the program everyday to check if there are any images modified that day!

When it comes to the weekend t's different because I need to get all images 2 day's old or newer!

Hope this explains it better!

Thanks

ST3VO
0
 
LVL 18

Expert Comment

by:Johnjces
Comment Utility
Someone will probably get you the answer and full code you desire, but in any case, here is a start. (Don't have Delphi right now to test or do much).

Use EncodeDate in SysUtils

Parse your text dates into its parts, turn the day, into the numeric day i.e., WED = 4, and do:

if EncodeDate(YearNow, MonthNow, DayNow) - 2 > EncodeDate(YearLastFri, MonthLastFri, DayLastFri) then
 ShowMessage('Today is greater than Last Friday by two days');

We would subtract 2  from the current date to adjust for the weekend or 2 days before today.

Might get ya going until I or someone else codes it all up for you.

Hope I helped a bit.

John
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LVL 3

Expert Comment

by:pablo_munoz
Comment Utility
I think I understand, but maybe you could clarify. You have 2 dates 11/01/2007 - 10/01/2007 , which one of these dated do you want to check against DateTime.Today.AddDays(-2)
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LVL 1

Expert Comment

by:tammoz
Comment Utility
hi
have a look on these tow functions and then decide what you want to do:
1.
function CompareDate(const ADate, BDate: TDateTime) : TValueRelationship

Compares two TDateTime values (returns "less", "equal" or "greater"). Ignores the Time part if both values "fall" on the same day.

TValueRelationship represents the relationship between two values. Each of three TValueRelationship values has a "liked" symbolic constant:
-1 [LessThanValue] The first value is less than the second value.
0 [EqualsValue] The two values are equal.
1 [GreaterThanValue] The first value is greater than the second value.

2.
function DayOfTheWeek ( const Date : TDateTime ) : Integer;

The DayOfTheWeek function returns an index number for the day of the week : 1  = Monday
2  = Tuesday
3  = Wednesday
4  = Thursday
5  = Friday
6  = Saturday
7  = Sunday
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Author Comment

by:ST3VO
Comment Utility
I think I would go for the first one!
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Author Comment

by:ST3VO
Comment Utility
Can I have some example code please?
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LVL 15

Accepted Solution

by:
mikelittlewood earned 500 total points
Comment Utility
Here is a way to convert that particular date format (Fri, 30 Nov 2007) you have back into a TDate property

function TForm1.convertToDate( const pDateString: string): TDate;
var
   dd, mm, yy: word;
   sl: TStringList;
begin
   sl := TStringList.Create;
   try
      sl.DelimitedText := pDateString;

      dd := strToInt( sl.Strings[ 1]);
      mm := monthVal( sl.Strings[ 2]);
      yy := strToInt( sl.Strings[ 3]);

      result := EncodeDate( yy, mm, dd);
   finally
      freeAndNil( sl)
   end;
end;

function TForm1.monthVal( const pMonth: string): smallInt;
var
   i: smallInt;
begin
   result := 0;
   for i := 1 to length( ShortMonthNames) do
      if ShortMonthNames[ i] = pMonth then
      begin
         result := i;
         break;
      end;
end;
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Author Comment

by:ST3VO
Comment Utility
That's for the conversion but what I really need is to compare dates....

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Expert Comment

by:tammoz
Comment Utility
I did not yet understand what you really want to do but this may help:

D1 is your date

case DayOfTheWeek(Now) of
    1..5:if D1 = now then
            ShowMessage('Done');
    6,7: if now - D1 <= 2 then
           ShowMessage('Done Weekend');
  else

  end;
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LVL 45

Expert Comment

by:aikimark
Comment Utility
You can get the file's timestamp directly using the FileAge() function.  You will need to convert this to a system date value with the FiledateToDateTime() function.

Example from:
http://www.delphibasics.co.uk/RTL.asp?Name=FileAge

var
  fileName   : string;
  fileDate   : Integer;

begin
  // Try to open the Unit1.DCU file for the current project
  fileName := 'Unit1.DCU';
  fileDate := FileAge(fileName);

  // Did we get the file age OK?
  if fileDate > -1 then
    ShowMessage(fileName+' last modified date = '+
                DateToStr(FileDateToDateTime(fileDate)));
end;

==================
other examples:
http://www.swissdelphicenter.ch/torry/showcode.php?id=142
http://www.festra.com/eng/snip03.htm
http://www.scalabium.com/faq/dct0046.htm

MP3 example from Borland:
http://codecentral.borland.com/Item/20163
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Author Comment

by:ST3VO
Comment Utility
The problem is that  the files I need to compare the dates from are online images.

Your example is local!

Would this work online?
0
 
LVL 45

Expert Comment

by:aikimark
Comment Utility
Are the image files on a LAN file server?  If so, YES.

If not, then what do mean by "online"?
0
 

Author Comment

by:ST3VO
Comment Utility
They are not on a LAN, They are images on the net!

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LVL 45

Expert Comment

by:aikimark
Comment Utility
please give us the URL and what method(s) you are using to look at the image files.
0
 

Author Closing Comment

by:ST3VO
Comment Utility
Done....Thanks to all for your time!
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LVL 45

Expert Comment

by:aikimark
Comment Utility
Note to international developers:

ShortMonthNames month names depend on the local settings.  Same is true for LongMonthNames array.
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