TDateTime to number

[molly]

@rvk:
Well, i've seen similar solutions using truncation beforehand.

I agree with your assessment. But, my agreement might not be considered 'normal

(effectively i was doing the same thing by truncating the data-time-value before handing it over to function DateTimeToUnix).

[ASerge]

Are there some lazarus/FP functions to convert a TDateTime to integer numbers and back again?

I need to compact a TDateTime to a string, before to save to a file.

I have tested DateTimeToFileDate() and FileDateToDateTime(), but FileDateToDateTime() not always restore the same date-time coded by DateTimeToFileDate().

What about DateTimeToTimeStamp and TimeStampToDateTime? Two LongInt or make one Int64, if you prefer one number.

[Edson]

What about DateTimeToTimeStamp and TimeStampToDateTime? Two LongInt or make one Int64, if you prefer one number.

Interesting suggestion. But I want to have only one number (the shorter possible). No need milliseconds precision by now.

But because DateTimeToStr only shows the truncated (to seconds) of a TDateTime you could end up with a difference if you don't truncate it the same way for DateTimeToUnix.

Yes. I also think it's deserable DateTimeToUnix() must works the same way DateTimeToStr() works, and in general, every Date-Time function in Lazarus.

But the main problem is that  DateTimeToUnix() is not reversible. 

[marcov]

dt * (3600*24)

[Paulo França Lacerda]

Already tried typecasting the TDateTime to Int64 and back?

Code: Pascal  [Select][+][-]

1. var
2.   I :Int64;
3.   D :TDateTime;
4. begin
5.   D := Now;
6.   I := Int64(D);  // pack
7.   D := TDateTime(I);  // unpack
8. end;

[molly]

Attempting to use simply casts unfortunately also fails. Operator overloading not allowed, and more of that, so:

Code: [Select]

Function DT2Number(dt: TDateTime): QWord; inline;
var
  dtq : Qword absolute dt;
begin
  Result := dtq;
end;


function Number2DT(n: QWord): TDateTime; inline;
var
  dtdt : TDateTime absolute n;
begin
  Result := dtdt;
end;


Already tried typecasting the TDateTime to Int64 and back?

Yes, it crashes;

[Paulo França Lacerda]

Already tried typecasting the TDateTime to Int64 and back?

Yes, it crashes;

This also works for me on Windows 7:

Code: Pascal  [Select][+][-]

1. function dt2int (dt:TDateTime) :Int64;
2. var I:Int64 absolute dt;
3. begin
4.   Result := I;
5. end;
6.  
7. function int2dt (I:Int64) :TDateTime;
8. var dt:TDateTime absolute I;
9. begin
10.   Result := dt;
11. end;

[molly]

This also works for me on Windows 7:

I do hope so, otherwise there is something serious amiss. I just did not wanted to sound too negative 

[Paulo França Lacerda]

This also works for me on Windows 7:

I do hope so, otherwise there is something serious amiss. I just did not wanted to sound too negative 

Although he (the post creator) is running on a 64-bit version of Windows 7. Mine is 32-bit.
This may be the key difference in the results.

[molly]

Sorry @patulinu.

My remark was a poor attempt of making a joke about why my example code uses QWord instead of Int64 (the QWord is used to express/store unsigned integer values, while an Int64 also allows for negative values).

[Paulo França Lacerda]

My remark was a poor attempt of making a joke about why my example code uses QWord instead of Int64 (the QWord is used to express/store unsigned integer values, while an Int64 also allows for negative values).

No problem about the joke. 
As for the QWord/Int64, I believe in this case both should work fine, provided no conversion is made, just raw-byte encapsulation.

P.S.: Since he's on a 64-bit platform, the QWord approach is probably the best solution.

[Remy Lebeau]

I need to compact a TDateTime to a string, before to save to a file.

Why not just encode the TDateTime in a standard ISO 8601 format?

[molly]

@Remy Lebeau:
TDateTime back-n-forth.

Are there msecs in ISO 8601 ? (i was unable to locate)

If not, then TS is running into the same issue.

[rvk]

Are there msecs in ISO 8601 ? (i was unable to locate)

Yes.

Decimal fractions may be added to any of the three time elements. However, a fraction may only be added to the lowest order time element in the representation.

[molly]

thank you very much rvk. (and sorry, as that's what you get when peeking too quickly over those pages).