在C#中怎么声明?
function Drum_InitCOM(COM:Integer): PChar; stdcall; external 'DrumCOM.DLL' name 'ConnectCOM';
function Drum_ExitCOM: PChar; stdcall; external 'DrumCOM.DLL' name 'DisConnectCOM';
function Drum_HatchOpen: PChar; stdcall; external 'DrumCOM.DLL' name 'HatchOpen';
function Drum_HatchClose: PChar; stdcall; external 'DrumCOM.DLL' name 'HatchClose';
function Drum_Rotate: PChar; stdcall; external 'DrumCOM.DLL' name 'DrumRotate';
function Drum_Status: PChar; stdcall; external 'DrumCOM.DLL' name 'DetectorStatus';
function Drum_HatchUp: PChar; stdcall; external 'DrumCOM.DLL' name 'HatchUp';
function Drum_HatchDown: PChar; stdcall; external 'DrumCOM.DLL' name 'HatchDown';
function Drum_Up: PChar; stdcall; external 'DrumCOM.DLL' name 'DrumUp';
function Drum_Down: PChar; stdcall; external 'DrumCOM.DLL' name 'DrumDown';
function Drum_Version: PChar; stdcall; external 'DrumCOM.DLL' name 'DrumVersion';