FSCTL_GET_COMPRESSION IOCTL (winioctl.h)

Retrieves the current compression state of a file or directory on a volume whose file system supports per-stream compression.

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

BOOL DeviceIoControl(
  (HANDLE) hDevice,             // handle to file
  FSCTL_GET_COMPRESSION,        // dwIoControlCode
  NULL,                         // lpInBuffer 
  0,                            // nInBufferSize
  (LPVOID) lpOutBuffer,         // output buffer
  (DWORD) nOutBufferSize,       // size of output buffer
  (LPDWORD) lpBytesReturned,    // number of bytes returned
  (LPOVERLAPPED) lpOverlapped   // OVERLAPPED structure
);

Remarks

The LZNT1 compression algorithm is the only compression algorithm implemented.

COMPRESSION_FORMAT_DEFAULT is not a compression state so it is not included in the table under the lpOutBuffer parameter. This value is only used with the FSCTL_SET_COMPRESSION control code.

If the file system of the volume containing the specified file or directory does not support per-file or per-directory compression, the operation fails.

You can set the compression state of a file or directory by using the FSCTL_SET_COMPRESSION control code. You can also compress or uncompress a file using this control code.

You can retrieve the compression attribute of a file or directory by calling the GetFileAttributes function. The compression attribute indicates whether a file or directory is compressed. The compression state indicates whether a file or directory is compressed, and, if it is, the format of the compressed data.

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

SMB 3.0 Transparent Failover and Scale-Out do not support NTFS compressed files. The FSCTL call is not blocked, but unsupported.

Requirements

See also

• DeviceIoControl
• FSCTL_SET_COMPRESSION
• File Compression and Decompression
• File Management Control Codes
• GetFileAttributes