Access Violation on clicking buttons and deleting text
lazarus / 9-Editor

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Paul-SFL · 2011-09-25 11:42

Hi all  ,

I finally wrote the calculator mode and now trying to connect it with
GUI. But somewhy I get access violation errors on testing the
calculator:
when type a number and then delete it by pressing BackSpace (error
when I delete the latest char);when clicking "+", "-" or "C" after
typing the numberwhen clicking "="
Unit references seems to be correct.. I have no idea on why  does it
happen  . The calculator "engine", gncalc, has been tested - works
100%-correctly, so I believe the problem is in unit2.

I'll appreciate very much if someone skims over the source and gives
me some advice.

I'm using Lazarus 0.9.30 + FRC 2.4.2.

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Blaazen · 2011-09-25 13:16

There are more bugs. It gives me SIGSEGV on closing the app.

Anyway, you should add there something like:
Code: [Select]procedure Tcalculator_mode.fieldChange(Sender: TObject);
     var s:string;
begin
  field.Readonly:=false;
  if length(field.text)=0 then exit;  //ADD THIS LINE
  if ((field.text[1]='-') and (length(field.text)>254)) or
(length(field.text)>253)       then         
because you are trying to read field.text[1] even if field.text is
empty.

EDIT:
You shouldn't have Application.Terminate on closing of main form. When
you close main form then app is terminated automaticly.
Code: [Select]procedure Tcalculator_mode.FormClose(Sender: TObject;
  var CloseAction: TCloseAction);
begin
//application.Terminate;
end;   

EDIT2:
Bug: You delete something and then you assign it ! :-)
Code: [Select]procedure Tcalculator_mode.plusClick(Sender: TObject);
begin
  gncalc.plus:=true;
  field.text:='';
  gncalc.Operand_0:=field.text;
end;    

must be :
Code: [Select]procedure Tcalculator_mode.plusClick(Sender: TObject);
begin
  gncalc.plus:=true;
  gncalc.Operand_0:=field.text;
  field.text:='';
end;    

And TMemo loses focus after pressing "C".

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Paul-SFL · 2011-09-25 17:33

Thank you a lot, Blaazen! It works!
Quote from: Blaazen on September 25, 2011, 03:16:55 pmCode: [Select] 
if length(field.text)=0 then exit;  //ADD THIS LINE  
Done.
Quote from: Blaazen on September 25, 2011, 03:16:55 pmYou shouldn't
have Application.Terminate on closing of main form. When you close
main form then app is terminated automaticly.
Thanks for the advice. Actually, I set calculator form to be main
temporarily  .
Quote from: Blaazen on September 25, 2011, 03:16:55 pmEDIT2:
Bug: You delete something and then you assign it ! :-)
Code: [Select]procedure Tcalculator_mode.plusClick(Sender: TObject);
begin
  gncalc.plus:=true;
  field.text:='';
  gncalc.Operand_0:=field.text;
end;    

must be :
Code: [Select]procedure Tcalculator_mode.plusClick(Sender: TObject);
begin
  gncalc.plus:=true;
  gncalc.Operand_0:=field.text;
  field.text:='';
end;    
Fixed. I also added to every button click procedure a boolean which
shows whether the first operand is entered, and if it's not - the
procedures are exited without doing anything.
Quote from: Blaazen on September 25, 2011, 03:16:55 pmAnd TMemo loses
focus after pressing "C".

Fixed too. BTW it's an interesting thing: TMemo loses focus on
pressing "=" or "C" and stays focused on pressing "+" or "-" - why
does it happen?

EDIT:
So, finally I've got it 100% working  .
Blaazen, thank you once more - you saved a lot of my time, I think.

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Blaazen · 2011-09-25 17:55

QuoteBTW it's an interesting thing: TMemo loses focus on pressing "="
or "C" and stays focused on pressing "+" or "-" - why does it happen?
Because "+" and "-" are TSpeedButton, which cannot be focused. "=" and
"C" are TButton.

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Paul-SFL · 2011-09-25 18:09

Thanks, got it  .