The FSCTL_SET_COMPRESSION DeviceIoControl operation sets the compression state of a file or directory on a volume whose file system supports per-file and per-directory compression. You can use this operation to compress or uncompress a file or directory on such a volume.
dwIoControlCode = FSCTL_SET_COMPRESSION; // operation code lpInBuffer ; // pointer to input buffer nInBufferSize ; // size of input buffer lpOutBuffer = NULL; // pointer to output buffer; not used; must be NULL nOutBufferSize = 0; // size of output buffer; not used; must be zero lpBytesReturned ; // pointer to DWORD used by DeviceIoControl function
The following values are defined:
Value |
Meaning |
COMPRESSION_FORMAT_NONE |
Uncompress the file or directory. |
COMPRESSION_FORMAT_DEFAULT |
Compress the file or directory, using the default compression format. |
COMPRESSION_FORMAT_LZNT1 |
Compress the file or directory, using the LZNT1 compression format. |
all other values |
Reserved for future use. |
If the operation succeeds, DeviceIoControl returns a nonzero value.
If the operation fails, DeviceIoControl returns zero. To get extended error information, call GetLastError.
On this release, LZNT1 is the only compression algorithm implemented. As a result, LZNT1 will be used as the DEFAULT compression method. Future releases may have additional compression methods which may be used as the DEFAULT.
If the file system of the volume containing the specified file or directory does not support per-file or per-directory compression, the FSCTL_SET_COMPRESSION operation fails.
Windows NT release 3.51 supports file compression on volumes formatted with NTFS.
The compression state change of the file or directory occurs synchronously with the call to DeviceIoControl.
You can obtain the compression state of a file or directory by using the FSCTL_GET_COMPRESSION DeviceIoControl operation.
You can obtain 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.
DeviceIoControl, FSCTL_GET_COMPRESSION, GetFileAttributes
file: /Techref/os/win/api/win32/func/src/f26_10.htm, 5KB, , updated: 2000/4/7 11:19, local time: 2024/11/8 21:10,
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