Delphi的指针为什么可以多次New

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, OrderList,
  Contnrs{虽然本单元中引入了OrderList，而OrderList里面引入了Contnrs，但是还是需要再引入一次};

type
  TForm1 = class(TForm)
    edt1: TEdit;
    lbl1: TLabel;
    btn1: TButton;
    btn2: TButton;
    lbl2: TLabel;
    edt2: TEdit;
    procedure btn1Click(Sender: TObject);
    procedure btn2Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

  PStudent = ^TStudent;
  TStudent = record
    name: string;
    age: Integer;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
var
  queue: TQueue;

procedure TForm1.btn1Click(Sender: TObject);
var
  student: PStudent;
begin
  New(student);
  student.name:= edt1.Text;
  student.age:= StrToInt(edt2.Text);

  try
    queue.Push(student);
  except
    on e: Exception do
    begin
      ShowMessage(e.Message);
    end;
  end;
end;

procedure TForm1.btn2Click(Sender: TObject);
var
  student: PStudent;
begin
  if queue.Count > 0 then
  begin
    New(student);
    student:= queue.Pop;

    Application.MessageBox(PChar(student.name+‘--‘+IntToStr(student.age)), ‘OK‘, MB_OK);
  end
  else
  //在这里加个判断队列是不是为空，就不会导致为空时出现异常
  begin
    Application.MessageBox(‘队列已经空了‘, ‘OK?‘, MB_OKCANCEL);
  end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  queue:= TQueue.Create;  //之前没有Create queue就直接进行Push，必然会出错
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  queue.Free;
end;

end.

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    btn1: TButton;
    procedure btn1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

  PStudent = ^TStudent;
  TStudent = record
    name: string;
    age: Integer;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.btn1Click(Sender: TObject);
var
  student: PStudent;
  st1: PStudent;
  st2: PStudent;
begin
  New(student);　　//使用New分配内存空间，并且student指针指向该内存空间
  student.name:= ‘st1‘;　　//通过指针student对该内存空间的结构体进行赋值操作
  student.age:= 10;

  st1:= student;　　//使用新的指针来指向student所指向的内存空间，保存原来内存空间的地址

  New(student);　　//再次New来分配空间，这时候student会指向新的内存空间，而因为之前进行了 st1:= student; 的操作，所以使用st1保存了原来的地址，而不会造成内存的丢失
  student.name:= ‘st2‘;　　//通过指针student 对新内存中的结构体赋值
  student.age:= 20;

  st2:= student;　　//再用st2 指针来保存新的内存地址

  ShowMessage(st1.name + ‘与‘ + st2.name);

  Dispose(st1);　　//使用完成后，使用Dispose(st1); 来释放原来的内存空间
  Dispose(st2);　　//其实此时Dispose(st2) 等价与 Dispose(student) 因为没有在上面进行 st2:= student 之后再次对student 进行New，所以st2与student指针都指向一个内存地址

end;

end.