回调函数的问题

Question

我做了一个DLL，调用主程序中的函数，总是报错。大虾们能不能帮我看看?DLL和主程序代码如下： 
library Project1;uses
  Wintypes,
  SysUtils,
  Dialogs,
  Classes;type
  Tintfunc=function (x:integer):integer;stdcall;function temp(x:integer;P:TFarProc):integer;stdcall;
begin
  //showmessage('ok');
  if P<>nil then result:=2*Tintfunc(p)(x);
end;
{$R *.RES}
exports
  temp;
begin
end.*********************************************
unit Unit2;interfaceuses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.DFM}function temp(x:integer;p:TfarProc):integer;stdcall;external 'project1.dll';function doub(x:integer):integer;
begin
  result:=2*x;
end;procedure TForm1.Button1Click(Sender: TObject);
begin
  Edit1.text:=inttostr(temp(10,@doub));
end;end.

Answer 1

library Project1;uses
  Wintypes,
  SysUtils,
  Dialogs,
  Classes;type
  Tintfunc=function (x:integer):integer;stdcall;function temp(x:integer;P:TFarProc):integer;stdcall;
begin
  //showmessage('ok');
  if P<>null then result:=2*Tintfunc(p)(x);/你这个地方错了*/
end;
{$R *.RES}
exports
  temp;
begin
end.*********************************************
unit Unit2;interfaceuses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.DFM}function temp(x:integer;p:TfarProc):integer;stdcall;external 'project1.dll';function doub(x:integer):integer;
begin
  result:=2*x;
end;procedure TForm1.Button1Click(Sender: TObject);
begin
  Edit1.text:=inttostr(temp(10,@doub));
end;end.