Device Control Codes

An application can use the DeviceIoControl function to send a control code to a device driver. The control code specifies the action that the driver is to perform. For example, a control code can ask a device driver to return information about the corresponding device, or direct the driver to carry out an action on the device, such as formatting a disk.

A number of standard control codes are defined in the Win32 header files. For a list of standard control codes, see DeviceIoControl . In addition, device drivers can define their own device-specific control codes. The types of control codes you can specify depend on the device being accessed and the Win32 platform on which your application is running.

Applications running on Windows NT can use the standard control codes or device-specific control codes to perform direct input and output operations on a floppy disk drive, hard disk drive, tape drive, or CD-ROM drive.

Win32-based applications running on Windows 95 cannot use the standard control codes in the Win32 header files. These applications are restricted to using the control codes supported by the virtual device driver being accessed. For example, the system VxD, VWIN32.VXD, supports the input and output control (IOCTL) functions originally provided by MS-DOS Interrupt 21h.

The control code specified in a DeviceIoControl call determines the values that must be specified for the other DeviceIoControl parameters. For example, a Windows NT application can specify the IOCTL_DISK_FORMAT_TRACKS control code. In this case, the lpvInBuffer parameter must point to a filled-in FORMAT_PARAMETERS structure, and the cbInBuffer parameter must specify the size of the structure.

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