看ddk源码的一些疑惑？

HANDLE
OpenUsbDevice( LPGUID  pGuid, char *outNameBuf)
/*++
Routine Description:

   Do the required PnP things in order to find
   the next available proper device in the system at this time.

Arguments:

    pGuid:      ptr to GUID registered by the driver itself
    outNameBuf: the generated name for this device

Return Value:

    return HANDLE if the open and initialization was successful,
else INVLAID_HANDLE_VALUE.
--*/
{
   ULONG NumberDevices;
   HANDLE hOut = INVALID_HANDLE_VALUE;
   HDEVINFO                 hardwareDeviceInfo;
   SP_INTERFACE_DEVICE_DATA deviceInfoData;
   ULONG                    i;
   BOOLEAN                  done;
   PUSB_DEVICE_DESCRIPTOR   usbDeviceInst;
   PUSB_DEVICE_DESCRIPTOR *UsbDevices = &usbDeviceInst;

   *UsbDevices = NULL;
   NumberDevices = 0;

   //
   // Open a handle to the plug and play dev node.
   // SetupDiGetClassDevs() returns a device information set that contains info on all
   // installed devices of a specified class.
   //
   hardwareDeviceInfo = SetupDiGetClassDevs (
                           pGuid,
                           NULL, // Define no enumerator (global)
                           NULL, // Define no
                           (DIGCF_PRESENT | // Only Devices present
                            DIGCF_INTERFACEDEVICE)); // Function class devices.

   //
   // Take a wild guess at the number of devices we have;
   // Be prepared to realloc and retry if there are more than we guessed
   //
   NumberDevices = 4;
   done = FALSE;
   deviceInfoData.cbSize = sizeof (SP_INTERFACE_DEVICE_DATA);

   i=0;
   while (!done) {
      NumberDevices *= 2;

      if (*UsbDevices) {
         *UsbDevices =
               realloc (*UsbDevices, (NumberDevices * sizeof (USB_DEVICE_DESCRIPTOR)));
      } else {
         *UsbDevices = calloc (NumberDevices, sizeof (USB_DEVICE_DESCRIPTOR));
      }

      if (NULL == *UsbDevices) {

         // SetupDiDestroyDeviceInfoList destroys a device information set
         // and frees all associated memory.

         SetupDiDestroyDeviceInfoList (hardwareDeviceInfo);
         return INVALID_HANDLE_VALUE;
      }

      usbDeviceInst = *UsbDevices + i;

      for (; i < NumberDevices; i++) {

         // SetupDiEnumDeviceInterfaces() returns information about device interfaces
         // exposed by one or more devices. Each call returns information about one interface;
         // the routine can be called repeatedly to get information about several interfaces
         // exposed by one or more devices.

         if (SetupDiEnumDeviceInterfaces (hardwareDeviceInfo,
                                         0, // We don't care about specific PDOs
pGuid,
                                         i,
                                         &deviceInfoData)) {

            hOut = OpenOneDevice (hardwareDeviceInfo, &deviceInfoData, outNameBuf);
if ( hOut != INVALID_HANDLE_VALUE ) {
               done = TRUE;
               break;
}
         } else {
            if (ERROR_NO_MORE_ITEMS == GetLastError()) {
               done = TRUE;
               break;
            }
         }
      }
   }

   NumberDevices = i;

   // SetupDiDestroyDeviceInfoList() destroys a device information set
   // and frees all associated memory.

   SetupDiDestroyDeviceInfoList (hardwareDeviceInfo);
   free ( *UsbDevices );
   return hOut;
}

就是这段代码，在2000ddk的src\wdm\usb\bulkusb\exe目录下

在网上很多的代码都是来自这里，可是

if (*UsbDevices) {
         *UsbDevices =
               realloc (*UsbDevices, (NumberDevices * sizeof (USB_DEVICE_DESCRIPTOR)));
      } else {
         *UsbDevices = calloc (NumberDevices, sizeof (USB_DEVICE_DESCRIPTOR));
      }

      if (NULL == *UsbDevices) {

         // SetupDiDestroyDeviceInfoList destroys a device information set
         // and frees all associated memory.

         SetupDiDestroyDeviceInfoList (hardwareDeviceInfo);
         return INVALID_HANDLE_VALUE;
      }
这一段到底是干什么用的呢，分配的空间并没有被使用

还有  NumberDevices = i;

最后把i值赋给NumberDevices，也没有实际使用啊

我在使用这段代码的时候，把guid设置好之后，在执行
SetupDiEnumDeviceInterfaces (hardwareDeviceInfo,
                                         0, // We don't care about specific PDOs
pGuid,
                                         i,
                                         &deviceInfoData)
之后，返回的是0，并且GetLastError()返回的是
ERROR_NO_MORE_ITEMS

偶是初学者，请多多指教，还有分就这么多，大家多包涵

顶一下