FSCTL_SET_ZERO_DATA

[This is preliminary documentation and subject to change.]

The FSCTL_SET_ZERO_DATA operation fills a specified range of a file with zeroes. If the file is sparse or compressed, NTFS may deallocate disk space within the file. This operation sets the range of bytes to zeroes without extending the file size. To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL DeviceIoControl(
  (HANDLE) hDevice,        // handle to a file
  FSCTL_SET_ZERO_DATA,     // dwIoControlCode, control code of
                           // operation to perform
  (LPVOID) lpInBuffer,     // pointer to buffer with input data
  (DWORD) nInBufferSize,   // size, in bytes, of lpInBuffer
  NULL,                    // lpOutBuffer is not used; must be NULL
  0,                       // nOutBufferSize is not used;
                           // must be zero
  (LPDWORD) lpBytesReturned,   // pointer to variable to receive
                           // output byte count
  (LPOVERLAPPED) lpOverlapped  // pointer to OVERLAPPED structure
                           // for asynchronous operation
);

Parameters

hDevice

Handle to the file on which the operation is to be performed. The file must be on an NTFS 5.0 file system or later. Call the CreateFile function to obtain a file handle. This operation cannot be called with any object other than a file.

dwIoControlCode

Control code for the operation. This value identifies the specific operation to be performed and the type of device on which the operation is to be performed. Use FSCTL_SET_ZERO_DATA for this operation.

lpInBuffer

Pointer to a FILE_ZERO_DATA_INFORMATION structure that specifies the range of the file to set to zeroes. The FileOffset member is the byte offset of the first byte to set to zeroes, and the BeyondFinalZero member is the byte offset of the first byte beyond the last zeroed byte.

nInBufferSize

Size, in bytes, of the input buffer.

lpOutBuffer

Pointer to the output buffer. Not used; must be NULL

nOutBufferSize

Size, in bytes, of the output buffer. Not used; must be zero.

lpBytesReturned

Pointer to a DWORD variable.

If lpOverlapped is NULL (nonoverlapped I/O), lpBytesReturned is used internally and cannot be NULL.

If lpOverlapped is not NULL (overlapped I/O), lpBytesReturned can be NULL.

lpOverlapped

Pointer to an OVERLAPPED structure.

If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, this parameter must point to a valid OVERLAPPED structure. In this case, DeviceIoControl is performed as an overlapped (asynchronous) operation. If the device was opened with the FILE_FLAG_OVERLAPPED flag and lpOverlapped is NULL, the function fails in unpredictable ways.

If hDevice was opened without specifying the FILE_FLAG_OVERLAPPED flag, this parameter is ignored and the DeviceIoControl function does not return until the operation has been completed, or until an error occurs.

Return Values

If the operation succeeds, DeviceIoControl returns a nonzero value.

If the operation fails, DeviceIoControl returns zero. For extended error information, call GetLastError.

Remarks

For the implications of overlapped I/O on this operation, see the Remarks section of the DeviceIoControl topic.

If you use the WriteFile function to write zeroes to a sparse file, the file system allocates disk space for the data that you are writing. If you use the FSCTL_SET_ZERO_DATA operation to write zeroes to a sparse file and the zeroed region is large enough, the file system may not allocate disk space.

QuickInfo

  Windows NT: Requires version 5.0 or later.
  Windows: Unsupported.
  Windows CE: Unsupported.
  Header: Declared in winioctl.h.

See Also

Device Input and Output Overview, Device Input and Output Operations, DeviceIoControl, FILE_ZERO_DATA_INFORMATION, FSCTL_QUERY_ALLOCATED_RANGES, FSCTL_SET_SPARSE