BY_HANDLE_FILE_INFORMATION structure (fileapi.h)

Contains information that the GetFileInformationByHandle function retrieves.

Syntax

typedef struct _BY_HANDLE_FILE_INFORMATION {
  DWORD    dwFileAttributes;
  FILETIME ftCreationTime;
  FILETIME ftLastAccessTime;
  FILETIME ftLastWriteTime;
  DWORD    dwVolumeSerialNumber;
  DWORD    nFileSizeHigh;
  DWORD    nFileSizeLow;
  DWORD    nNumberOfLinks;
  DWORD    nFileIndexHigh;
  DWORD    nFileIndexLow;
} BY_HANDLE_FILE_INFORMATION, *PBY_HANDLE_FILE_INFORMATION, *LPBY_HANDLE_FILE_INFORMATION;

Members

dwFileAttributes

The file attributes. For possible values and their descriptions, see File Attribute Constants.

ftCreationTime

A FILETIME structure that specifies when a file or directory is created. If the underlying file system does not support creation time, this member is zero (0).

ftLastAccessTime

A FILETIME structure. For a file, the structure specifies the last time that a file is read from or written to. For a directory, the structure specifies when the directory is created. For both files and directories, the specified date is correct, but the time of day is always set to midnight. If the underlying file system does not support the last access time, this member is zero (0).

ftLastWriteTime

A FILETIME structure. For a file, the structure specifies the last time that a file is written to. For a directory, the structure specifies when the directory is created. If the underlying file system does not support the last write time, this member is zero (0).

dwVolumeSerialNumber

The serial number of the volume that contains a file.

nFileSizeHigh

The high-order part of the file size.

nFileSizeLow

The low-order part of the file size.

nNumberOfLinks

The number of links to this file. For the FAT file system this member is always 1. For the NTFS file system, it can be more than 1.

nFileIndexHigh

The high-order part of a unique identifier that is associated with a file. For more information, see nFileIndexLow.

nFileIndexLow

The low-order part of a unique identifier that is associated with a file.

The identifier (low and high parts) and the volume serial number uniquely identify a file on a single computer. To determine whether two open handles represent the same file, combine the identifier and the volume serial number for each file and compare them.

The ReFS file system, introduced with Windows Server 2012, includes 128-bit file identifiers. To retrieve the 128-bit file identifier use the GetFileInformationByHandleEx function with FileIdInfo to retrieve the FILE_ID_INFO structure. The 64-bit identifier in this structure is not guaranteed to be unique on ReFS.

Remarks

The identifier that is stored in the nFileIndexHigh and nFileIndexLow members is called the file ID. Support for file IDs is file system-specific. File IDs are not guaranteed to be unique over time, because file systems are free to reuse them. In some cases, the file ID for a file can change over time.

In the FAT file system, the file ID is generated from the first cluster of the containing directory and the byte offset within the directory of the entry for the file. Some defragmentation products change this byte offset. (Windows in-box defragmentation does not.) Thus, a FAT file ID can change over time. Renaming a file in the FAT file system can also change the file ID, but only if the new file name is longer than the old one.

In the NTFS file system, a file keeps the same file ID until it is deleted. You can replace one file with another file without changing the file ID by using the ReplaceFile function. However, the file ID of the replacement file, not the replaced file, is retained as the file ID of the resulting file.

Not all file systems can record creation and last access time, and not all file systems record them in the same manner. For example, on a Windows FAT file system, create time has a resolution of 10 milliseconds, write time has a resolution of 2 seconds, and access time has a resolution of 1 day (the access date). On the NTFS file system, access time has a resolution of 1 hour. For more information, see File Times.

Requirements

See also

FILETIME

FILE_ID_INFO

File Attribute Constants

GetFileInformationByHandle

GetFileInformationByHandleEx