card reader ( no memory stick is inserted )

Question

Grretings to all..

i have a card reader ( no memory stick is inserted ).

when i insert into my compter it shows a drive in My Computer...

why it shows like that....

Is it possible to know whether a drive is having a media ( sorry i am not sure how to call it ) or not...

Answer 1

The reason for this behavior is historical, and dates back to floppy drives and MS-DOS. The A: drive would still be the A: drive even if there was no floppy in it.

It is sometimes possible to check whether a drive with removable media is empty. Card readers and CD drives usually support this, floppy drives don't. You would send the drive a IOCTL_STORAGE_CHECK_VERIFY .

Answer 2

I find the suggestion of MSalters to use IOCTL_STORAGE_CHECK_VERIFY very good. There are a small trick in the usage of IOCTL_STORAGE_CHECK_VERIFY. Before the usage of IOCTL code in the function DeviceIoControl one need to open the corresponding device with respect of CreateFile function:

HANDLE hDevice = CreateFile (szDeviceName,  // like "\\.\E:"
                             0,             // no access to the drive
                             FILE_SHARE_READ | FILE_SHARE_WRITE, // share mode
                             NULL, OPEN_EXISTING, 0, NULL);

For the usage of DeviceIoControl one can use 0 as a second parameter of CreateFile, because we will not use ReadFile, WriteFile etc functions to access the device. The implementation of IOCTL_STORAGE_CHECK_VERIFY do follow to some read of data requests. So to be able to use IOCTL_STORAGE_CHECK_VERIFY without having ERROR_ACCESS_DENIED (5) error we have to open the device as following

HANDLE hDevice = CreateFile (szDeviceName,  // like "\\.\E:"
                             FILE_READ_DATA, // read access to the data
                             FILE_SHARE_READ | FILE_SHARE_WRITE, // share mode
                             NULL, OPEN_EXISTING, 0, NULL);

There exist another version of IOCTL_STORAGE_CHECK_VERIFY - IOCTL_STORAGE_CHECK_VERIFY2 which works absolutely the same as IOCTL_STORAGE_CHECK_VERIFY but much more quickly (see http://msdn.microsoft.com/en-us/library/ff560538.aspx). To use IOCTL_STORAGE_CHECK_VERIFY2 one can open device with only FILE_READ_ATTRIBUTES access:

HANDLE hDevice = CreateFile (szDeviceName,         // like "\\.\E:"
                             FILE_READ_ATTRIBUTES, // read access to the attributes
                             FILE_SHARE_READ | FILE_SHARE_WRITE, // share mode
                             NULL, OPEN_EXISTING, 0, NULL);

The code which test the existence of the media in the drive can look like following

DWORD cbBytesReturned;
bSuccess = DeviceIoControl (hDevice,                     // device to be queried
                            IOCTL_STORAGE_CHECK_VERIFY2,
                            NULL, 0,                     // no input buffer
                            NULL, 0,                     // no output buffer
                            &cbBytesReturned,            // # bytes returned
                            (LPOVERLAPPED) NULL);        // synchronous I/O
if (bSuccess)
    _tprintf (TEXT("the device media are accessible\n"));
else if (GetLastError() == ERROR_NOT_READY)
    _tprintf (TEXT("the device media are not accessible\n"));