CODEWITHSUNDEEP
delphierror-handling
Omair Iqbal
Omair Iqbal

Reputation: 1838

getting "E2197 Constant object cannot be passed as var parameter" when passing var parameter

this code works fine: 

procedure TForm2.Timer1Timer(Sender: TObject);
var
  Text: string;
begin  SetLength (Text,555);
  GetWindowText (getforegroundwindow, PChar (Text),555);
  Form2.gtListBox1.Items.Add (
    IntToStr (getforegroundwindow) + ': ' + Text);
end;

but when i put

var
  Text: string;

from Timer1Timer event handler to units implementation section or ''text : string'' in the units var section i get error : E2197 Constant object cannot be passed as var parameter
according to documentation :

This error message appears when you try to send a constant as a var or out parameter for a function or procedure.

but i didnt declared text as constant then why am i getting this error?
Edit:@mason wheeler: i do not understand than why does this work:

implementation
{$R *.dfm}
 var 
 char :integer;//first of all why does delphi let me declare variable that is also a type name
procedure TForm2.Button1Click(Sender: TObject);
begin
char:=11; 
showmessage(IntToStr(char));
end;

my first code was not working because i declared text as string ,you say : ''the compiler might think it's a reference to the type and not to the variable'' than why doesnt the compiler think its a reference to the type and not to the variable in this case? i am confused
Edit2: i now understand what was wrong but still have 1 confusion i did'nt use a with statement then why delphi is treating as if i am using: 

 with
      form1 do
       text := 'blahblahblah';

this is wrong on the delphi part i mean delphi should not let us do text := 'blah' but form1.text := blah; or with form1 do text := 'blah'; do i need to turn on/off some compiler setting(s) i am using delphi 2010 without any ide experts

Upvotes: 3

Views: 4258

Answers (3)

Mason Wheeler
Mason Wheeler

Reputation: 84550

With regard to your Edit #2:

That's a standard convention of object-oriented programming. When you're writing a method for an object, the code is implicitly interpreted as being in the scope of the object. In other words, every object method can be considered as being inside a hidden with self do block.

Upvotes: 1

Bharat
Bharat

Reputation: 6866

Actually if you declare Text in implementation section and use it in Timer1Timer(Sender: TObject), compiler will consider Text as Form1.Text.

Change the name of text as sText and it will work.

Edit 1:

Because there is no property/Field for form like Form1.Char.

Upvotes: 5

Mason Wheeler
Mason Wheeler

Reputation: 84550

It's probably a name confusion. "Text" is a type name as well, a legacy textfile type. So if you declare the variable in a different scope, the compiler might think it's a reference to the type and not to the variable. Try naming it something else and it should work.

Upvotes: 2

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