I have always avoided using a for-loop index variable after the loop. I thought its value can be unpredictable in some situations when the compiler reuses its register or memory etc.

I noticed the ActionListEditor in Lazarus sources has code that uses it after the loop.
The compiler, FPC 3.0, does not warn about it.
I made a small test:

procedure MyProcedure;
var
  i: Integer;
begin
  for i := 0 to 5 do
    WriteLn('iii ', i);
  Write('After loop i=', i);
  if i = 5 then
    WriteLn(' as expected')
  else
    WriteLn(' which is unpredictable');
end;

Indeed, no warning!
Is it OK to do that? Have I misunderstood it?

Juha

Juha Manninen wrote on Mon, 10 Oct 2016:

I have always avoided using a for-loop index variable after the loop. I thought its value can be unpredictable in some situations when the compiler reuses its register or memory etc.

That is correct.

The compiler, FPC 3.0, does not warn about it.

Indeed: http://bugs.freepascal.org/view.php?id=12508

Jonas

Hi, if you mean this:
 
function CategoryIndexOf(Name: String): Integer;
  var
    i: Integer;
  begin
    for i:= lstCategory.Items.Count-1 downto 0 do begin       if lstCategory.Items[i] = Name
      then Break;
    end;
    Result := i;
    if (i = lstCategory.Items.IndexOf(cActionListEditorUnknownCategory))        and (i = lstCategory.Items.IndexOf(cActionListEditorAllCategory))     then Result := 0;
  end;
 
It can IMO cause random and hardly reproducible bugs.  
V.
______________________________________________________________

I have always avoided using a for-loop index variable after the loop. I thought its value can be unpredictable in some situations when the compiler reuses its register or memory etc.

I noticed the ActionListEditor in Lazarus sources has code that uses it after the loop.

Juha

Vojtěch Čihák wrote

Hi, if you mean this: ...

Yes, that is one of them.
The code does not make sense in any case, regardless of "i"'s value. Index for cActionListEditorUnknownCategory and
cActionListEditorAllCategory differ.
"i" cannot have both at the same time. Maybe the condition should be "or", not "and".
Why does it not compare Name directly with
cActionListEditorUnknownCategory and cActionListEditorAllCategory constants?

There are many similar fishy code blocks. I will sanitize some of them ...

Juha

Vojtěch Čihák wrote

      then Break;  

Isn't leaving for loop with break only case, where loop variable will keep the value. Otherwise it is undefined.
But it does make the code more confusing.