Question

qt 判断指针对象是否释放

Answer 1

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unit Unit1;

interface

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

type
TA = class
private
Fs: string;
public
constructor Create(s: string);
destructor Destroy;override;
procedure test;
end;

TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
A: TA;
begin
A := TA.Create('test');
A.Free;
//A := nil;
//if A <> nil then
if Assigned(A) then
A.test;
end;

{ TA }

constructor TA.Create(s: string);
begin
Fs:= s;
end;

destructor TA.Destroy;
begin
Fs:= '';
inherited;
end;

procedure TA.test;
begin
ShowMessage(Fs);
end;

end.

例如以上代码，A对象所指向的堆内存已经free了，但无论判断A是否为nil或者用assigned判断，都可以调用A.test而不出错。应该怎么判断A已经Free而不至于执行A.test呢？

Answer 2

只能是释放的时候给指针赋值Null 然后判断指针是否为null吧