DeviceIoControl function (ioapiset.h)

Sends a control code directly to a specified device driver, causing the corresponding device to perform the corresponding operation.

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BOOL DeviceIoControl(
  [in]                HANDLE       hDevice,
  [in]                DWORD        dwIoControlCode,
  [in, optional]      LPVOID       lpInBuffer,
  [in]                DWORD        nInBufferSize,
  [out, optional]     LPVOID       lpOutBuffer,
  [in]                DWORD        nOutBufferSize,
  [out, optional]     LPDWORD      lpBytesReturned,
  [in, out, optional] LPOVERLAPPED lpOverlapped


[in] hDevice

A handle to the device on which the operation is to be performed. The device is typically a volume, directory, file, or stream. To retrieve a device handle, use the CreateFile function. For more information, see Remarks.

[in] dwIoControlCode

The control code for the operation. This value identifies the specific operation to be performed and the type of device on which to perform it.

For a list of the control codes, see Remarks. The documentation for each control code provides usage details for the lpInBuffer, nInBufferSize, lpOutBuffer, and nOutBufferSize parameters.

[in, optional] lpInBuffer

A pointer to the input buffer that contains the data required to perform the operation. The format of this data depends on the value of the dwIoControlCode parameter.

This parameter can be NULL if dwIoControlCode specifies an operation that does not require input data.

[in] nInBufferSize

The size of the input buffer, in bytes.

[out, optional] lpOutBuffer

A pointer to the output buffer that is to receive the data returned by the operation. The format of this data depends on the value of the dwIoControlCode parameter.

This parameter can be NULL if dwIoControlCode specifies an operation that does not return data.

[in] nOutBufferSize

The size of the output buffer, in bytes.

[out, optional] lpBytesReturned

A pointer to a variable that receives the size of the data stored in the output buffer, in bytes.

If the output buffer is too small to receive any data, the call fails, GetLastError returns ERROR_INSUFFICIENT_BUFFER, and lpBytesReturned is zero.

If the output buffer is too small to hold all of the data but can hold some entries, some drivers will return as much data as fits. In this case, the call fails, GetLastError returns ERROR_MORE_DATA, and lpBytesReturned indicates the amount of data received. Your application should call DeviceIoControl again with the same operation, specifying a new starting point.

If lpOverlapped is NULL, lpBytesReturned cannot be NULL. Even when an operation returns no output data and lpOutBuffer is NULL, DeviceIoControl makes use of lpBytesReturned. After such an operation, the value of lpBytesReturned is meaningless.

If lpOverlapped is not NULL, lpBytesReturned can be NULL. If this parameter is not NULL and the operation returns data, lpBytesReturned is meaningless until the overlapped operation has completed. To retrieve the number of bytes returned, call GetOverlappedResult. If hDevice is associated with an I/O completion port, you can retrieve the number of bytes returned by calling GetQueuedCompletionStatus.

[in, out, optional] lpOverlapped

A pointer to an OVERLAPPED structure.

If hDevice was opened without specifying FILE_FLAG_OVERLAPPED, lpOverlapped is ignored.

If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, the operation is performed as an overlapped (asynchronous) operation. In this case, lpOverlapped must point to a valid OVERLAPPED structure that contains a handle to an event object. Otherwise, the function fails in unpredictable ways.

For overlapped operations, DeviceIoControl returns immediately, and the event object is signaled when the operation has been completed. Otherwise, the function does not return until the operation has been completed or an error occurs.

Return value

If the operation completes successfully, the return value is nonzero (TRUE).

If the operation fails or is pending, the return value is zero. To get extended error information, call GetLastError.


To retrieve a handle to the device, you must call the CreateFile function with either the name of a device or the name of the driver associated with a device. To specify a device name, use the following format:


DeviceIoControl can accept a handle to a specific device. For example, to open a handle to the logical drive A: with CreateFile, specify \\.\a:. Alternatively, you can use the names \\.\PhysicalDrive0, \\.\PhysicalDrive1, and so on, to open handles to the physical drives on a system.

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 OPEN_EXISTING.
  • 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.
For lists of supported control codes, see the following topics:


For an example that uses DeviceIoControl, see Calling DeviceIoControl.


Requirement Value
Minimum supported client Windows XP
Minimum supported server Windows Server 2003
Target Platform Windows
Header ioapiset.h (include Windows.h)
Library Kernel32.lib
DLL Kernel32.dll

See also



Device Input and Output Control (IOCTL)




Assign drive letter sample