FSCTL_SET_ZERO_DATA IOCTL (winioctl.h)

Fills a specified range of a file with zeros (0). If the file is sparse or compressed, the NTFS file system may deallocate disk space in the file. This sets the range of bytes to zeros (0) 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
  (LPVOID) lpInBuffer,              // input buffer
  (DWORD) nInBufferSize,            // size of input buffer
  NULL,                             // lpOutBuffer
  0,                                // nOutBufferSize
  (LPDWORD) lpBytesReturned,        // number of bytes returned
  (LPOVERLAPPED) lpOverlapped       // OVERLAPPED structure
);

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 zeros (0) 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 control code to write zeros (0) to a sparse file and the zero (0) region is large enough, the file system may not allocate disk space.

If you use the FSCTL_SET_ZERO_DATA control code to write zeros (0) to a non-sparse file, zeros (0) are written to the file. The system allocates disk storage for all of the zero (0) range, which is equivalent to using the WriteFile function to write zeros (0) to a file.

The time stamps may not be updated correctly for a remote file. To ensure consistent results, use unbuffered I/O.

In Windows 8 and Windows Server 2012, this code is supported by the following technologies.

Requirements

See also

• DeviceIoControl
• FILE_ZERO_DATA_INFORMATION
• FSCTL_QUERY_ALLOCATED_RANGES
• FSCTL_SET_SPARSE
• File Management Control Codes
• Sparse Files