Device Handles

A DeviceIoControl call specifies a handle of a device driver to identify the device being accessed. You can use the CreateFile function to get a device driver 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 Win32 platform on which your application is running.

On Windows NT, DeviceIoControl can open a handle of 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.

For Win32-based applications running on Windows 95, DeviceIoControl must specify a handle of a virtual device driver. For example, to open a handle to the system VxD, specify "\\\\.\\vwin32".

The CreateFile call should specify the FILE_SHARE_READ and FILE_SHARE_WRITE access flags when opening a handle to a device driver. However, when opening a communications resource, such as a serial port, CreateFile must specify exclusive access. Other CreateFile parameters are used 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.

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