Delphi Union 使用

Union部分只能放在最后，这和C的不太一样，要放在前面先用Type定义一个单独的Union类型就可以了。

unit Unit1;

interface

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

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

type
  TMyUnion = packed record
    ID: Integer;
//    case Boolean of
//      true: (cmd: DWORD);
//      false: (hiCmd:Word;loCmd:Word);

//    case Byte of
//    0: (cmd: DWORD);
//    1: (hiCmd:Word;loCmd:Word);

//    case Integer of
//    0: (cmd: DWORD);
//    1: (hiCmd:Word;loCmd:Word);

    case aCmd:Integer of
    0: (cmd: DWORD);
    1: (hiCmd:Word;loCmd:Word);

  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var
  tmp: TMyUnion;
begin
  tmp.ID := 10;
  tmp.cmd := $0000FFFF;
  tmp.aCmd := 100;
  ShowMessageFmt('%d',[SizeOf(TMyUnion)]);
  ShowMessageFmt('%d',[tmp.hiCmd]);
  ShowMessageFmt('%d',[tmp.aCmd]);
  Application.Terminate;
end;

end.