datetime comparison

[bobbygm]

HI!

I NEED HELP!!

I have problems while comparing two dates in
tdatetime format with Delphi 7.
I compare the two variables either by > or
by the comparedatetime function, and the
result of the comparison seems to be unpredictable.
It doesn't give correct results, and I don't know
why.
Any good advice??
Thank u

Emanuele

 

[towerbase]

Can you post some code which demonstrates the problem? Please show any error messages or evidence of why you are not getting the results you expect.

Andrew
Hampshire, UK

 

[bobbygm]

this is the code statement:

if comparedate(data_tm,data_old)>=0 then ...

(data_tm and data_old are both variables of Tdatetime type)

and this is part of a log file in which I manually
added an ending "---" to indicate a wrong result and "-"
to indicate equal values (this is a lesser problem):

41859A3W --- 29-nov-04 11:52:22 < 09-feb-89 18:16:32---
41860A3W --- 17-mar-89 14:44:06 < 13-giu-94 15:31:28
41958A3W --- 17-mar-89 14:45:40 < 13-giu-94 15:33:20
41988A3W --- 06-lug-99 11:45:22 < 14-apr-89 12:50:02---
41989A3W --- 09-feb-04 8:49:50 < 19-apr-89 9:30:50---
41990A1W --- 27-giu-00 8:31:04 < 03-mar-89 17:05:42---
41991A3W --- 04-mag-89 11:13:48 < 04-mag-89 11:13:48-
41992A3W --- 27-apr-89 9:40:48 < 27-apr-89 9:40:48-
41993A3W --- 23-feb-89 9:52:56 < 23-feb-89 9:52:56-
41994A3W --- 31-gen-89 11:17:24 < 31-gen-89 11:17:24-
42015A3W --- 25-nov-88 11:33:00 < 19-mar-97 12:36:40
42017A3W --- 25-nov-88 18:56:12 < 06-mag-97 9:45:56
42019A3W --- 22-feb-89 16:05:36 < 19-mar-97 12:38:30
42026A3M --- 19-apr-89 9:41:58 < 19-apr-89 9:41:58-
42030A4M --- 07-dic-88 17:23:50 < 07-dic-88 17:23:50-
42056A4M --- 25-mag-89 18:16:06 < 22-apr-94 18:12:36
42015A3W --- 10-apr-96 17:05:18 < 19-mar-97 12:36:40
42017A3W --- 10-apr-96 18:29:06 < 06-mag-97 9:45:56
42019A3W --- 08-giu-94 16:57:18 < 19-mar-97 12:38:30
42026A3M --- 09-feb-04 8:54:08 < 19-apr-89 9:41:58---
42027A4M --- 12-giu-04 11:43:22 < 07-dic-88 17:17:24---
42028A1W --- 01-mar-90 14:30:56 < 01-mar-90 14:30:56-
42030A4M --- 02-mag-89 15:04:52 < 07-dic-88 17:23:50---
42044A3I --- 27-apr-89 9:57:02 < 09-gen-89 9:52:24---

Thank u for your attention!

Emanuele

 

[bobbygm]

P.S. the log file is obtained by re-converting to
string the tdatetime values by the datetimetostr
function.

I noticed that the wrong results are in correspondance
with a second year previous to 1990. Can it be of some
importance?

Emanuele

 

[Pikkunero]

Which version of Delphi are you using? I don't seem to have CompareDate function and i'm using D5Ent.

Or is it in a 3rd party library?

 

[bobbygm]

I'm using D7 ent.
You should include "dateutils" in the "uses" section.
Anyhow, "comparedate(a,b)>=0" is much the same as
"a>=b", when a and b are tdatetime.
If I use "a>=b", the program generates the same log file.

 

[Pikkunero]

No dateutils in D5 ent. I can try to replicate the error. I'll post it here if i have any success.

 

[towerbase]

You haven't supplied the actual code that produces the error.

For example, I produced a test program, using Delphi 7, that contained two TMonthCalender objects called A and B, a TButton and a TLabel and wrote this code for the OnClick handler of the TButton:

Uses DateUtils;

procedure TForm1.Button1Click(Sender: TObject);
begin
  case CompareDate ( A.Date, B.Date ) of
  -1: Label1.Caption := 'A is earlier than B';
   0: Label1.Caption := 'A is the sames as B';
  +1: Label1.Caption := 'A is later than B';
  end;
end;

CompareDate works perfectly okay in these circumstances with the test dates I used.

Please create a small test program that demonstrates the problem and copy and paste the code so that we can examine it. I am 99.99% sure that the error will be in your coding.

Andrew
Hampshire, UK

 

[Pikkunero]

Now after towerbase's example it seems that you're only checking for positive result of CompareDate function.

if comparedate(data_tm,data_old)>=0 then ...

As towerbase's example shows you should infact use a 'case' statement instead of 'if'.

 

[bobbygm]

Ok, now the CODE is:

case comparedate(data_tm, data_old) of
1 : BLOGGER1.Logga(num_dis+' --- '+data_str+' > '+data_old_str);
0 : BLOGGER1.Logga(num_dis+' --- '+data_str+' = '+data_old_str);
-1 : BLOGGER1.Logga(num_dis+' --- '+data_str+' < '+data_old_str);
end;

with
data_tm, data_old : tdatetime
data_str:= datetimetostr(data_tm)
data_old_str:= datetimetostr(data_old)

BLOGGER1 is a simple component with a procedure "logga" that opens a log file and
writes text lines in it.

and the log file still shows the same results.

Is it possible that the problem arises from D7-english being installed in an Italian Win2000 environment?
I checked the proper OS date-time format settings, and they should be ok.

 

[towerbase]

You still haven't shown us your actual code. For example, whereabouts is data_str and data_old_str being assigned?

Anyway, can you amend your case statement so that the actual numeric values of data_tm and data_old are logged then you should be able to see (and log) the actual values being compared.

I suggest you use the Format function to make life easier.

Something like:

const
  GT = '%s --- %s > %s. %f %f';
  EQ = '%s --- %s = %s. %f %f';
  LT = '%s --- %s < %s. %f %f';
...
case comparedate(data_tm, data_old) of
 1: BLOGGER1.Logga(Format(GT,[num_dis,data_str,data_old_str,data_tm,data_old));
 0: BLOGGER1.Logga(Format(EQ,[num_dis,data_str,data_old_str,data_tm,data_old));
-1: BLOGGER1.Logga(Format(LT,[num_dis,data_str,data_old_str,data_tm,data_old));
end;

Andrew
Hampshire, UK

 

[bobbygm]

Thank u very much for your advice.
Now the log file shows, for instance:

41859A3W --- 29-nov-04 11:52:22 < 09-feb-89 18:16:32. 38320,49 69073,76

something is obviously wrong.
the assignment to data_old is made by the following
dbExpress sqlquery and code:

SELECT num_dis, dir_dis, data_dis
FROM disegni
WHERE num_dis= ...
... SQLquery1.open ...
data_old:= fields.Fields[2].Asdatetime;

the field "data_dis" is of type "date" on an Oracle
database.

Where's the problem??
Thanks again

 

[Zathras]

69073,76 is interpreted as 09-02-2089 18:14:24

38320,49 is interpreted as 29-11-2004 11:45:36

The problem appears to be a difference in the way Delphi and and your DBMS interpret 2-digit year values.

Since your DB is returning a date number of 69073 (year = 2089), I would say the real problem is where the data are being captured and stored in the DB originally.

 

[bobbygm]

OK.

Now that I know exactly where the problem is,
I can solve it (I hope).

Thanks for your attention and precision!

Emanuele