Stupid behaviour of Memo1.Lines.Strings[100]

[anna]

Why access to Memo1.Lines.Strings[100] doesn't  occur error if  Memo1 has less than 100 lines?
For example TStrings variable in same conditions occurs error 'Bla-bla out of bounds'.
I need error. I know that it is possible to check count manually, but it's stupid.

[Troodon]

Is Memo1.Lines.Strings[100] allocated/assigned? Does it have a value?

Update: Same behavior in Delphi.

[typo]

SynEdit has the same behavior. ShowMessage(SynEdit.Lines[100]) returns an empty string.

[anna]

Is Memo1.Lines.Strings[100] allocated/assigned? Does it have a value?

Memo1 has 1 to 99 lines. I've put  Memo1 on form. By default it has one string 'Memo1'.
So then for example put edit1 & button1 & write for Button1Click

Code: [Select]

procedure TForm1.Button1Click(Sender: TObject);
begin
  edit1.text:=Memo1.Lines.Strings[100];
end;   . If click button1 , i cannot see error. Nay, sometimes Edit1 gets abra-kadabra.  Edit1 must get either empty string or error message, but abra-kadabra from non-allocated memory is bad.

[eny]

I know that it is possible to check count manually, but it's stupid.

As a general rule one shouldn't access a list outside it's bounds.
Therefore a check for the line count is a good thing.
As for the number 100, we shouldn't use magic numbers anyway.

I do however agree with the fact that it's weird that no exception is thrown.

[Marc]

An edit with 99 lines of text and a CRLF and the end of the last line has in fact 100 lines. The last being empty. So getting line[100] should not cause an error in this case, but it should return an empty string and not some random garbage

[Wodzu]

An edit with 99 lines of text and a CRLF and the end of the last line has in fact 100 lines. The last being empty. So getting line[100] should not cause an error in this case, but it should return an empty string and not some random garbage

Clever explanation but in case of Memo it does not throwing an excepetion for any line number greater than 100.

[Marc]

err...
That looks like a bug. Can you bugrep this ?

[Wodzu]

Ok, I will.

http://bugs.freepascal.org/view.php?id=16260

[clauslack]

With Delphi 5
ShowMessage(Memo1.Lines[Memo1.Lines.Count + 50]);

show an empty string.

Is the default behaviour ?

Regards

[Wodzu]

In Delphi 2007 behaviour is the same. Even with "Range checking" options.
Strange...

[Marc]

Rangechecking has nothing to do with the checking if list indexes

[Bart]

From my notes in bugtracker:

Delphi uses the EM_GETLINE Message to retrieve the text.
A return value of 0 indicates no chars were returned.
AFAICS there is no way to determine if this is because Index is out of range, or because the line is empty (at least not for a memo control).
(See: http://msdn.microsoft.com/en-us/library/bb761584(VS.85).aspx)

> And the more important, is it the right behaviour?

From: http://docwiki.embarcadero.com/VCL/en/Classes.TStrings.Strings
> Descendants of TStrings must implement an accessor function for the Strings
> property to return the string at the position indicated by Index. Index gives
> the position of the string, where 0 is the first string, 1 is the second
> string, and so on.

By this definition the behaviour when Index is out of bounds is undefined.

Bart