Delphi static variable

Question

In my class, i need to use a static variable ( static int next_id; in C++)

I use

private
    class var next_id: Integer;

I get Error : PROCEDURE or FUNCTION expected. How to declare some variable with Delphi 5 ?

Answer 1

In Delphi 5, you can't. No class vars in Delphi 5 yet.

The next best thing is a global variable in the implementation section of the unit, though.

unit Whatever;

...

implementation

var
  next_ID: Integer;

...

initialization
  next_ID := 0;

end.

Or alternatively, at the very bottom:

begin
  next_ID := 0;
end.

Answer 2

Expanding on Rudy's answer...

Delphi 5 did not yet have this available. But you could at least declare a global variable. I won't copy Rudy's code, but I will add that in order to initialize them (and clean them up if necessary), you should use the initialization (and finalization) sections of a unit. These go on the very bottom of a Delphi unit, like so...

unit Whatever;

...

interface

...

implementation

...

initialization
  MyGlobalVar := TMyGlobalVar.Create;
finalization
  FreeAndNil(MyGlobalVar);
end.

Or in your case...

initialization
  next_ID := 1;

And your scenario in particular won't require a finalization section.

Answer 3

Sample of class variable declaration:

unit Unit2;

interface

type
  GlobalData = class
    class var V1: String;
    class var X1: Integer;
  end;

implementation

end.

usage sample from other unit:

procedure TForm1.FormCreate(Sender: TObject);
begin
  GlobalData.V1 := 'Yahoo';
end;

you don't need to create and destroy this class. it will be created automatically before everything else.

what is wrong in your sample: class variable must be declared inside class. i don't see class declaration in your sample. plus, as was mentioned before, Delphi 5 (very very old) do not support this feature.