The stat structure type is used to return information about the
attributes of a file. It contains at least the following members:
mode_t st_mode
- Specifies the mode of the file. This includes file type information
(see Testing File Type) and the file permission bits
(see Permission Bits).
ino_t st_ino
- The file serial number, which distinguishes this file from all other
files on the same device.
dev_t st_dev
- Identifies the device containing the file. The
st_ino and
st_dev , taken together, uniquely identify the file. The
st_dev value is not necessarily consistent across reboots or
system crashes, however.
nlink_t st_nlink
- The number of hard links to the file. This count keeps track of how
many directories have entries for this file. If the count is ever
decremented to zero, then the file itself is discarded as soon as no
process still holds it open. Symbolic links are not counted in the
total.
uid_t st_uid
- The user ID of the file's owner. See File Owner.
gid_t st_gid
- The group ID of the file. See File Owner.
off_t st_size
- This specifies the size of a regular file in bytes. For files that are
really devices this field isn't usually meaningful. For symbolic links
this specifies the length of the file name the link refers to.
time_t st_atime
- This is the last access time for the file. See File Times.
unsigned long int st_atime_usec
- This is the fractional part of the last access time for the file.
See File Times.
time_t st_mtime
- This is the time of the last modification to the contents of the file.
See File Times.
unsigned long int st_mtime_usec
- This is the fractional part of the time of the last modification to the
contents of the file. See File Times.
time_t st_ctime
- This is the time of the last modification to the attributes of the file.
See File Times.
unsigned long int st_ctime_usec
- This is the fractional part of the time of the last modification to the
attributes of the file. See File Times.
blkcnt_t st_blocks
- This is the amount of disk space that the file occupies, measured in
units of 512-byte blocks.
The number of disk blocks is not strictly proportional to the size of
the file, for two reasons: the file system may use some blocks for
internal record keeping; and the file may be sparse--it may have
"holes" which contain zeros but do not actually take up space on the
disk.
You can tell (approximately) whether a file is sparse by comparing this
value with
st_size , like this:
(st.st_blocks * 512 < st.st_size)
This test is not perfect because a file that is just slightly sparse
might not be detected as sparse at all. For practical applications,
this is not a problem.
unsigned int st_blksize
- The optimal block size for reading of writing this file, in bytes. You
might use this size for allocating the buffer space for reading of
writing the file. (This is unrelated to
st_blocks .)
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