This macro creates a unique system I/O control code (IOCTL).

#define CTL_CODE(DeviceType, Function, Method, Access) (((DeviceType) << 16) | ((Access) << 14) | ((Function) << 2) | (Method)
)

Parameters（参数）

DeviceType

Defines the type of device for the given IOCTL.

This parameter can be no bigger than a WORD value.

The values used by Microsoft are in the range 0-32767; the values 32768-65535 are reserved for use by OEMs and IHVs.

The following device types are defined by the system:

• FILE_DEVICE_BEEP
• FILE_DEVICE_CD_ROM
• FILE_DEVICE_CD_ROM_FILE_SYSTEM
• FILE_DEVICE_CONTROLLER
• FILE_DEVICE_DATALINK
• FILE_DEVICE_DFS
• FILE_DEVICE_DISK
• FILE_DEVICE_DISK_FILE_SYSTEM
• FILE_DEVICE_FILE_SYSTEM
• FILE_DEVICE_INPORT_PORT
• FILE_DEVICE_KEYBOARD
• FILE_DEVICE_MAILSLOT
• FILE_DEVICE_MIDI_IN
• FILE_DEVICE_MIDI_OUT
• FILE_DEVICE_MOUSE
• FILE_DEVICE_MULTI_UNC_PROVIDER
• FILE_DEVICE_NAMED_PIPE
• FILE_DEVICE_NETWORK
• FILE_DEVICE_NETWORK_BROWSER
• FILE_DEVICE_NETWORK_FILE_SYSTEM
• FILE_DEVICE_NULL
• FILE_DEVICE_PARALLEL_PORT
• FILE_DEVICE_PHYSICAL_NETCARD
• FILE_DEVICE_PRINTER
• FILE_DEVICE_SCANNER
• FILE_DEVICE_SERIAL_MOUSE_PORT
• FILE_DEVICE_SERIAL_PORT
• FILE_DEVICE_SCREEN
• FILE_DEVICE_SOUND
• FILE_DEVICE_DEVICE_STREAMS
• FILE_DEVICE_TAPE
• FILE_DEVICE_TAPE_FILE_SYSTEM
• FILE_DEVICE_TRANSPORT
• FILE_DEVICE_UNKNOWN
• FILE_DEVICE_VIDEO
• FILE_DEVICE_VIRTUAL_DISK
• FILE_DEVICE_WAVE_IN
• FILE_DEVICE_WAVE_OUT
• FILE_DEVICE_8042_PORT
• FILE_DEVICE_NETWORK_REDIRECTOR
• FILE_DEVICE_BATTERY
• FILE_DEVICE_BUS_EXTENDER
• FILE_DEVICE_MODEM
• FILE_DEVICE_VDM
• FILE_DEVICE_MASS_STORAGE
• FILE_DEVICE_SMB
• FILE_DEVICE_KS
• FILE_DEVICE_CHANGER
• FILE_DEVICE_SMARTCARD
• FILE_DEVICE_ACPI
• FILE_DEVICE_DVD
• FILE_DEVICE_FULLSCREEN_VIDEO
• FILE_DEVICE_DFS_FILE_SYSTEM
• FILE_DEVICE_DFS_VOLUME

The following device types are specific to Windows CE:

• FILE_DEVICE_HAL
• FILE_DEVICE_CONSOLE
• FILE_DEVICE_PSL
• FILE_DEVICE_SERVICE

Function

Defines an action within the device category.

Function codes 0-2047 are reserved for Microsoft; codes 2048-4095 are reserved for OEMs and IHVs.

A function code can be no larger then 4095.

Method

Defines the method codes for how buffers are passed for I/O and file system controls.

The following values are possible for this parameter:

• METHOD_BUFFERED
• METHOD_IN_DIRECT
• METHOD_OUT_DIRECT
• METHOD_NEITHER

This field is ignored by Windows CE. You should always use the METHOD_BUFFERED value unless compatibility with Windows-based desktop platforms is required using a different Method value.

Access

Defines the access check value for any access.

The following table shows the possible flags for this parameter. The FILE_ACCESS_ANY is generally the correct value.

Flag	Description
FILE_ANY_ACCESS	Request all access.
FILE_READ_ACCESS	Request read access. Can be used with FILE_WRITE_ACCESS.
FILE_WRITE_ACCESS	Request write access. Can be used with FILE_READ_ACCESS.

Return Values（返回值）

None.

Remarks（备注）

The macro can be used for defining IOCTL and FSCTL function control codes. All IOCTLs must be defined this way to ensure that values used by Microsoft, OEMs, and IHVs do not overlap.

The following illustration shows the format of the resulting IOCTL.

举例说明一下：

我定义两个IOCTL,一个用于对设备的读，一个用于对设备的写

#define ATST2004_IOCTL_READ CTL_CODE(FILE_DEVICE_UNKNOWN, 0x800, METHOD_BUFFERED, FILE_READ_DATA)
#define ATST2004_IOCTL_WRITE CTL_CODE(FILE_DEVICE_UNKNOWN, 0x801, METHOD_BUFFERED, FILE_WRITE_DATA)

在VC中使用不需要进行处理，假如我要在VB中使用这两个IOCTL，就需要进行查值计算了，计算后定义如下：

Private Const ATST2004_IOCTL_READ = &H226000
Private Const ATST2004_IOCTL_WRITE = &H22A004

关于Method（I/O访问内存使用方式），我们下篇在说。