Delphi中函数定义和声明的位置

　　当函数（或过程）A定义在函数（或过程）B之前，那么函数B就可以调用函数A，并且编译成功，例如下面的

procedure TForm1.btn1Click(Sender: TObject); 和   function showstr: string;

unit Test;



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;



var

  Form1: TForm1;



implementation



{$R *.dfm}





function showstr: string;

begin

  Result:= 'lala';

end;



procedure TForm1.btn1Click(Sender: TObject);

begin

   ShowMessage(showstr);

end;



end.

　

　　　当函数（或过程）A定义在函数（或过程）B之后，那么如果函数B调用函数A，在编译时会报错，如下面的例程

还是procedure TForm1.btn1Click(Sender: TObject); 和   function showstr: string;

unit Test;



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;



var

  Form1: TForm1;



implementation



{$R *.dfm}



procedure TForm1.btn1Click(Sender: TObject);

begin

   ShowMessage(showstr);

end;



function showstr: string;      //showstr在TForm1.btn1Click后定义，且没有在它之前进行声明

begin

  Result:= 'lala';

end;



end.

　　要想当函数（或过程）A定义在函数（或过程）B之后，并且函数B调用函数A，在编译时不报错，那就需要现在B前面声明A，然后再在B中调用A，这时候无论A在B之前定义还是在B之后定义，都能够编译成功。如下面的例程

unit Test;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



function showstr: string;    //首先在interface里面声明





type

  TForm1 = class(TForm)

    btn1: TButton;

    procedure btn1Click(Sender: TObject);

  private

    { Private declarations }

  public

    { Public declarations }

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}





function showstr: string;

begin

  Result:= 'lala';

end;



procedure TForm1.btn1Click(Sender: TObject);

begin

   ShowMessage(showstr);

end;



end.