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  • 学习官方示例 System.Assigned

    unit Unit1;
    
    interface
    
    uses
      Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
      Dialogs, StdCtrls;
    
    type
      TForm1 = class(TForm)
        Button1: TButton;
        Button2: TButton;
        procedure Button1Click(Sender: TObject);
        procedure Button2Click(Sender: TObject);
      end;
    
    var
      Form1: TForm1;
    
    implementation
    
    {$R *.dfm}
    
    var
      p1: Pointer;
    
    procedure TForm1.Button1Click(Sender: TObject);
    var
      b1,b2,b3,b4: Boolean;
    begin
      //p1 := nil;
      b1 := Assigned(p1);
    
      GetMem(p1, 1024);
      b2 := Assigned(p1);
    
      FreeMem(p1, 1024);
      b3 := Assigned(p1);
    
      p1 := nil;
      b4 := Assigned(p1);
    
      ShowMessageFmt('%s, %s, %s, %s', [BoolToStr(b1,True),
                                        BoolToStr(b2,True),
                                        BoolToStr(b3,True),
                                        BoolToStr(b4,True)]); {False, True, True, False}
    end;
    
    procedure TForm1.Button2Click(Sender: TObject);
    var
      p2: Pointer;
      b1,b2,b3,b4: Boolean;
    begin
      p2 := nil;
      b1 := Assigned(p2);
    
      GetMem(p2, 1024);
      b2 := Assigned(p2);
    
      FreeMem(p2, 1024);
      b3 := Assigned(p2);
    
      p2 := nil;
      b4 := Assigned(p2);
    
      ShowMessageFmt('%s, %s, %s, %s', [BoolToStr(b1,True),
                                        BoolToStr(b2,True),
                                        BoolToStr(b3,True),
                                        BoolToStr(b4,True)]); {False, True, True, False}
    end;
    
    end.
    
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  • 原文地址:https://www.cnblogs.com/del/p/1288772.html
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