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Doesn't Free() and Release() check for nil-pointers?

Hi.

I'm creating a form at runtime, like this:

ControlWindow := TControlWIndow.Create(MainWindow);

When I am done using the form, I call the Release() -method like this:

if Assigned(ControlWindow) then
ControlWindow.Release;

My question is this:
When I check the memoryusage via AllocMemCount, first it shows 452. After I have created ControlWindow it shows 683, and after I have Released ControlWIndow it shows 472. Why is there a difference of 20 (472 - 452)..? Shouldn't it show 452 after Release too?

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robert_marquardt

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robert_marquardt

BTW where is the connection to nil Pointers?

esoftbg

Let see an example:

//........ Project
program Q_21145490;

uses
Forms,
Unit1_Q_21145490 in 'Unit1_Q_21145490.pas' {Form1},
Unit2_Q_21145490 in 'Unit2_Q_21145490.pas' {Form2};

{$R *.res}

begin
Application.Initialize;
Application.CreateForm(TForm1, Form1);
Application.Run;
end.

//........ Form1

unit Unit1_Q_21145490;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, Buttons;

type
TForm1 = class(TForm)
SpeedButton1: TSpeedButton;
SpeedButton2: TSpeedButton;
procedure SpeedButton1Click(Sender: TObject);
procedure SpeedButton2Click(Sender: TObject);
private { Private declarations }
public { Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

uses
Unit2_Q_21145490;

procedure TForm1.SpeedButton1Click(Sender: TObject);
begin
Application.CreateForm(TForm2, Form2);
Form2.Show;
end;

procedure TForm1.SpeedButton2Click(Sender: TObject);
begin
if Assigned(Form2) then
Form2.Release;
if Assigned(Form2) then
Form2.Release;
end;

end.

//........ COMMENT:

Form2.Release; // does not make Form2 := nil;

so it is better to use:

procedure TForm1.SpeedButton2Click(Sender: TObject);
begin
if Assigned(Form2) then
begin
Form2.Release;
Form2 := nil;
end;
if Assigned(Form2) then
Form2.Release;
end;

Emil

esoftbg

so it is better to use:

procedure TForm1.SpeedButton2Click(Sender: TObject);
begin
if Assigned(Form2) then
begin
Form2.Release;
Form2 := nil;
end;
end;

Emil

esoftbg

it is better to use:

procedure TForm1.SpeedButton1Click(Sender: TObject);
begin
if not Assigned(Form2) then
Application.CreateForm(TForm2, Form2);
Form2.Show;
end;