CTL_CODE說明

本文轉自http://blog.csdn.net/lujunql/archive/2008/06/10/2532362.aspx

咱們在說DeviceIoControl函數時其第二個參數dwIoControlCode就是由CTL_CODE宏定義的，下邊咱們能夠了解一下CTL_CODE的內容。

CTL_CODE：用於建立一個惟一的32位系統I/O控制代碼，這個控制代碼包括4部分組成：DeviceType（設備類型，高16位（16-31位）），Access（訪問限制，14-15位），Function（功能2-13位），Method（I/O訪問內存使用方式）。

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（參數）

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（備註）

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.

舉例說明一下：

我定義兩個IOCTL,一個用於對設備的讀，一個用於對設備的寫

#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中使用不須要進行處理，假如我要在VB中使用這兩個IOCTL，就須要進行查值計算了，計算後定義以下：

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