FSCTL_SET_ZERO_ON_DEALLOCATION control code

Applies to: desktop apps only

Indicates an NTFS file system file handle should have its clusters filled with zeros when it is deallocated. If a file is resident, it is converted to nonresident. When clusters are deallocated, the clusters on a disk are zeroed. If a file is deleted, all clusters associated with the file are zeroed.

To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL 
WINAPI 
DeviceIoControl( (HANDLE) hDevice,               // handle to device
                 FSCTL_SET_ZERO_ON_DEALLOCATION, // dwIoControlCode
                 NULL,                           // lpInBuffer
                 0,                              // nInBufferSize
                 NULL,                           // lpOutBuffer
                 0,                              // nOutBufferSize
                 (LPDWORD) lpBytesReturned,      // number of bytes returned
                 (LPOVERLAPPED) lpOverlapped );  // OVERLAPPED structure

Parameters

hDevice

A handle to the device. To obtain a device handle, call the CreateFile function.

dwIoControlCode

The control code for the operation. Use FSCTL_SET_ZERO_ON_DEALLOCATION for this operation.

lpInBuffer

Not used with this operation.

Set to NULL.

nInBufferSize

Not used with this operation.

Set to 0 (zero).

lpOutBuffer

Not used with this operation.

Set to NULL.

nOutBufferSize

Not used with this operation.

Set to 0 (zero).

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, the call fails, GetLastError returns ERROR_INSUFFICIENT_BUFFER, and lpBytesReturned is zero.

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.

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, DeviceIoControl returns a nonzero value.

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

Requirements

See also

DeviceIoControl

File Management Control Codes

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Build date: 4/17/2012