help! Is this a bug?
lazarus / 13-General

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Neo2010 · 2010-01-27 13:21

Hello to everyone!
I wonder can anybody tell me whether this is a bug -- When "Verify
method calls"(Compiler options for project --> code) is checked, such
code as below will report run error:

procedure TForm1.Button1Click(Sender: TObject);
var
  J: Integer;
begin
  J := -1;
  if 1 in [0..J] then
    ShowMessage('OK');
end; 


Best regards and many thx!

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theo · 2010-01-27 13:29

I don't think it is a (FPC) bug.

Like this, it doesn't even compile:

Code: [Select]procedure TForm1.Button1Click(Sender: TObject);
const K=-1;
begin
  if 1 in [0..K] then
    ShowMessage('OK');
end;

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Neo2010 · 2010-01-28 01:08

Thank you theo!
But in Delphi my code doesn't generate any  runtime error, so I'm
really confused if this is fpc's special featrue which is designed to
be different with Delphi or something else?

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Paul Ishenin · 2010-01-28 01:37

This is a new feature for FPC and some things that delphi allows can
fail. I will look at this issue but better if you create a bug report
so this will not be forgotten.

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Neo2010 · 2010-01-28 05:25

Many Thanks, Paul

Because I don't know where to post a bug report, and I think even this
really is a bug, it is a negligible "bug", so I will not create a bug
report. But if you can fix in the future version of fpc, I will reall
appreciate it.

Best regards to every one!

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Paul Ishenin · 2010-01-28 05:52

Oups, sorry. I misread your code. I read it as

for i in [0..K] then
  ShowMessage('OK');

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Paul Ishenin · 2010-01-28 05:58

By the way, I checked you code with fpc 2.5.1 and everything works ok.
I see 'OK' message box and no runerror.

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Neo2010 · 2010-01-28 09:05

I have retested my code:

procedure TForm1.Button1Click(Sender: TObject);
var
  I, J: Integer;
begin
  J := -1;
  I := 1;
  if I in [0..J] then
    ShowMessage('runtime error not found');

end;

and was totally confused.

if "Verify method calls" option is not checked, then it will generate
no runtime error, but the msg 'runtime error not found' will show,
which means 1 is in [0..-1](totally wrong! because an empty set can't
have any element mathematically speaking).

If "Verify method calls" option is  checked, then a runtime error will
be throw out.

This is getting more and more interesting. Can anybody help test this
code again, thanks!



compile environment:
fpc 2.5.1
laz 0.9.29
OS: win32  xp sp2

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theo · 2010-01-28 10:04

Afaik, a set can not contain negative values (only byte range).

That explains why it doesn't compile if "J" is a const (see my
example).
That explains why it does "bullshit" at runtime with no err.
chechking.
That explains why it throws a runtime error with err. checking on.

It's not that misterious imho.

Maybe things have changed in FPC 2.5.1
You can ask the FPC developers in the FPC mailing lists:
http://www.freepascal.org/maillist.var

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Neo2010 · 2010-01-28 11:00

Theo, many thanks!
You're right, I rechecked the ref of fpc, it does say that the base
type of Set can only be ordinal type with arange between 0 and 255. So
my code is wrong, fpc is right. Case closed!
Enjoy fpc and Laz!
Best regards!