我的代码如下：
HANDLE OpenOneDevice(HDEVINFO hDveInfo,PSP_INTERFACE_DEVICE_DATA DvcInfoData,
                     char *sDevNameBuf)
{
   HANDLE hOut = INVALID_HANDLE_VALUE;
   ULONG iReqLen = 0;
   SetupDiGetInterfaceDeviceDetail（ DveInfo,DvcInfoData,
                                    NULL,0,&iReqLen,NULL);
   ULONG iDevDataLen = iReqLen;
   PSP_INTERFACE_DEVICE_DETAIL_DATA pDevData;
   pDevData = (PSP_INTERFACE_DEVICE_DETAIL_DATA)malloc(iDevDataLen);
   pDevData->cbSize = sizeof(SP_INTERFACE_DEVICE_DETAIL_DATA);
   bool bResult = SetupDiGetInterfaceDeviceDetail(hDveInfo,DvcInfoData,
                  pDevData,iDevDataLen,&iReqLen,NULL);
   if(bResult == true)
   {
      strcpy(sDevNameBuf,pDevData->DevicePath);
      hOut = CreateFile(pDevData->DevicePath ,
                        GENERIC_READ|GENERIC_WRITE,
                        FILE_SHARE_READ|FILE_SHARE_WRITE,
                        NULL,
                       OPEN_EXISTING,0,NULL);
   }
   free(pDevData);
   return hOut;
}   
//-----------------------------------------------------------
HANDLE OpenUsbDevice(const GUID *pGuid,char *sDevNameBuf)
{
    HANDLE hOut = INVALID_HANDLE_VALUE;
    HDEVINFO hDevInfo ;
    ULONG n;
    SP_INTERFACE_DEVICE_DATA deviceInfoData;
    hDevInfo = SetupDiGetClassDevs(pGuid,
                                   NULL,
                                   NULL,
                                   DIGCF_PRESENT|DIGCF_INTERFACEDEVICE);
    if(hDevInfo == INVALID_HANDLE_VALUE)
    {
       return NULL ;
    }
    deviceInfoData.cbSize = sizeof(SP_DEVINFO_DATA);
    ULONG nGuessCount = MAXLONG;
    for(ULONG iDevIndex=0; iDevIndex<nGuessCount; iDevIndex++)
   {
      if(SetupDiEnumDeviceInterfaces(hDevInfo, 0, pGuid, 
                                   iDevIndex, &deviceInfoData))
      {
        hOut=OpenOneDevice(hDevInfo, &deviceInfoData, sDevNameBuf）；
        if(hOut != INVALID_HANDLE_VALUE)
          break;
      }
      n =  GetLastError();
      if( n == ERROR_NO_MORE_ITEMS) //No more items
      {
        break;
      }
   }
  SetupDiDestroyDeviceInfoList(hDevInfo);
  return hOut;
} 
这段代码 SetupDiEnumDeviceInterfaces的返回值永远都是false,这是为什么啊，n的值是259，pGuid 是机器上的USB设备，比如U盘   。请大虾仁兄帮忙分析一下