Device Handles

When you call the DeviceIoControl function, you must specify a handle that identifies the device to access. You can use the CreateFile function to get a device handle.

The CreateFile call must specify either the name of a device or the name of the driver associated with a device. To specify a device name, the lpszname parameter of CreateFile specifies a string with the format

\\.\DeviceName 
 

The types of devices that you can open and the method that you must use to specify them in the CreateFile function depend on the platform on which your application is running.

• Windows NT/2000: The DeviceIoControl function can open a handle to a specific device. For example, to open a handle to the logical drive A:, specify "\\\\.\\a:". Alternatively, you can use the names "\\\\.\\PhysicalDrive0", "\\\\.\\PhysicalDrive1", and so on, to open handles to the physical drives on a system.
• Windows 95/98: For Win32-based applications, DeviceIoControl must specify a handle to a virtual device driver. For example, to open a handle to the system VxD, specify "\\\\.\\vwin32".

You should specify the FILE_SHARE_READ and FILE_SHARE_WRITE access flags when calling CreateFile to open a handle to a device driver. However, when you open a communications resource, such as a serial port, you must specify exclusive access. Use the other CreateFile parameters as follows when opening a device handle:

• The fdwCreate parameter must specify the OPEN_EXISTING flag.
• The hTemplateFile parameter must be NULL.
• The fdwAttrsAndFlags parameter can specify FILE_FLAG_OVERLAPPED to indicate that the returned handle can be used in overlapped (asynchronous) I/O operations.