Last modified on 6 June 2013, at 03:50

C Programming/POSIX Reference/sys/stat.h

<sys/stat.h> is the header in the C POSIX library for the C programming language that contains constructs that facilitate getting information about files attributes.

Member functionsEdit

Name Notes
int stat (const char *filename, struct stat *buf) The stat function returns information about the attributes of the file named by filename in the structure pointed to by buf. If filename is the name of a symbolic link, the attributes you get describe the file that the link points to. If the link points to a nonexistent file name, then stat fails reporting a nonexistent file. The return value is 0 if the operation is successful, or -1 on failure. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is in fact stat64 since the LFS interface transparently replaces the normal implementation.

errno Errors: ENOENT means the file named by filename doesn't exist.

int stat64 (const char *filename, struct stat64 *buf) This function is similar to stat but it is also able to work on files larger than 2^31 bytes on 32-bit systems. To be able to do this the result is stored in a variable of type struct stat64 to which buf must point. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is available under the name stat and so transparently replaces the interface for small files on 32-bit machines.

errno Errors: ENOENT means the file named by filename doesn't exist.

int fstat (int filedes, struct stat *buf) The fstat function is like stat, except that it takes an open file descriptor (filedes)as an argument instead of a file name. Like stat, fstat returns 0 on success and -1 on failure. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is in fact fstat64 since the LFS interface transparently replaces the normal implementation.

errno Errors: EBADF means the filedes argument is nos a valid file descriptor.

int fstat64 (int filedes, struct stat64 *buf) This function is similar to fstat but is able to work on large files on 32-bit platforms. For large files the file descriptor filedes should be obtained by open64 or creat64. The buf pointer points to a variable of type struct stat64 which is able to represent the larger values. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is available under the name fstat and so transparently replaces the interface for small files on 32-bit machines.

errno Errors: EBADF means the filedes argument is nos a valid file descriptor.

int lstat (const char *filename, struct stat *buf) The lstat function is like stat, except that it does not follow symbolic links. If filename is the name of a symbolic link, lstat returns information about the link itself; otherwise lstat works like stat. See Symbolic Links. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is in fact lstat64 since the LFS interface transparently replaces the normal implementation.
int lstat64 (const char *filename, struct stat64 *buf) The lstat function is like stat, except that it does not follow symbolic links. If filename is the name of a symbolic link, lstat returns information about the link itself; otherwise lstat works like stat. See Symbolic Links. When the sources are compiled with _FILE_OFFSET_BITS == 64 this function is in fact lstat64 since the LFS interface transparently replaces the normal implementation.

Member constantsEdit

The following POSIX macros are defined to check the file type using the st_mode field:

Name Notes
S_ISREG(m) is it a regular file?
S_ISDIR(m) is it a directory?
S_ISCHR(m) is it a character device?
S_ISBLK(m) is it a block device?
S_ISFIFO(m) is it a FIFO (named pipe)?
S_ISLNK(m) is it a symbolic link? (Not in POSIX.1-1996.)
S_ISSOCK(m) is it a socket? (Not in POSIX.1-1996.)

The following flags are defined for the st_mode field:

Name Value Notes
S_IFMT 0170000 bit mask for the file type bit fields
S_IFSOCK 0140000 socket
S_IFLNK 0120000 symbolic link
S_IFREG 0100000 regular file
S_IFBLK 0060000 block device
S_IFDIR 0040000 directory
S_IFCHR 0020000 character device
S_IFIFO 0010000 FIFO
S_ISUID 0004000 set UID bit
S_ISGID 0002000 set-group-ID bit (see below)
S_ISVTX 0001000 sticky bit (see below)
S_IRWXU 00700 mask for file owner permissions
S_IRUSR 00400 owner has read permission
S_IWUSR 00200 owner has write permission
S_IXUSR 00100 owner has execute permission
S_IRWXG 00070 mask for group permissions
S_IRGRP 00040 group has read permission
S_IWGRP 00020 group has write permission
S_IXGRP 00010 group has execute permission
S_IRWXO 00007 mask for permissions for others (not in group)
S_IROTH 00004 others have read permission
S_IWOTH 00002 others have write permission
S_IXOTH 00001 others have execute permission

The set-group-ID bit (S_ISGID) has several special uses. For a directory it indicates that BSD semantics is to be used for that directory: files created there inherit their group ID from the directory, not from the effective group ID of the creating process, and directories created there will also get the S_ISGID bit set. For a file that does not have the group execution bit (S_IXGRP) set, the set-group-ID bit indicates mandatory file/record locking. The sticky bit (S_ISVTX) on a directory means that a file in that directory can be renamed or deleted only by the owner of the file, by the owner of the directory, and by a privileged process.

POSIX does not describe the S_IFMT, S_IFSOCK, S_IFLNK, S_IFREG, S_IFBLK, S_IFDIR, S_IFCHR, S_IFIFO, S_ISVTX bits, but instead demands the use of the macros S_ISDIR(), etc. The S_ISLNK() and S_ISSOCK() macros are not in POSIX.1-1996, but both are present in POSIX.1-2001; the former is from SVID 4, the latter from SUSv2.

Other Systems - Values that have been (or are) in use on various systems:

hex name ls octal description
f000 S_IFMT 170000 mask for file type
0000 000000 SCO out-of-service inode; BSD unknown type; SVID-v2 and XPG2 have both 0 and 0100000 for ordinary file
1000 S_IFIFO p| 010000 FIFO (named pipe)
2000 S_IFCHR c 020000 character special (V7)
3000 S_IFMPC 030000 multiplexed character special (V7)
4000 S_IFDIR d/ 040000 directory (V7)
5000 S_IFNAM 050000 XENIX named special file with two subtypes, distinguished by st_rdev values 1, 2
0001 S_INSEM s 000001 XENIX semaphore subtype of IFNAM
0002 S_INSHD m 000002 XENIX shared data subtype of IFNAM
6000 S_IFBLK b 060000 block special (V7)
7000 S_IFMPB 070000 multiplexed block special (V7)
8000 S_IFREG - 100000 regular (V7)
9000 S_IFCMP 110000 VxFS compressed
9000 S_IFNWK n 110000 network special (HP-UX)
a000 S_IFLNK l@ 120000 symbolic link (BSD)
b000 S_IFSHAD 130000 Solaris shadow inode for ACL (not seen by userspace)
c000 S_IFSOCK s= 140000 socket (BSD; also "S_IFSOC" on VxFS)
d000 S_IFDOOR D> 150000 Solaris door
e000 S_IFWHT w% 160000 BSD whiteout (not used for inode)
0200 S_ISVTX 001000 sticky bit: save swapped text even after use (V7) reserved (SVID-v2). On non-directories: don’t cache this file (SunOS). On directories: restricted deletion flag (SVID-v4.2)
0400 S_ISGID 002000 set-group-ID on execution (V7) for directories: use BSD semantics for propagation of GID
0400 S_ENFMT 002000 SysV file locking enforcement (shared with S_ISGID)
0800 S_ISUID 004000 set-user-ID on execution (V7)
0800 S_CDF 004000 directory is a context dependent file (HP-UX)

A sticky command appeared in Version 32V AT&T UNIX.

Member typesEdit

Data types defined in the <sys/stat.h> header include:

struct stat {
  dev_t     st_dev;     /* ID of device containing file */
  ino_t     st_ino;     /* inode number */
  mode_t    st_mode;    /* protection */
  nlink_t   st_nlink;   /* number of hard links */
  uid_t     st_uid;     /* user ID of owner */
  gid_t     st_gid;     /* group ID of owner */
  dev_t     st_rdev;    /* device ID (if special file) */
  off_t     st_size;    /* total size, in bytes */
  blksize_t st_blksize; /* blocksize for file system I/O */
  blkcnt_t  st_blocks;  /* number of blocks allocated */
  time_t    st_atime;   /* time of last access */
  time_t    st_mtime;   /* time of last modification */
  time_t    st_ctime;   /* time of last status change */
};

ExampleEdit

A short example of <sys/stat.h> usage is:

/**************************************************************
 abstract ls meaning
 **************************************************************/
#include <stdio.h>
#include <sys/stat.h>
#include <string.h>
#include <errno.h>
 
int            main(int argc, char **argv)
{
  struct stat  file_stat;
 
  while (argc-- > 1)
    {
      if (lstat(argv[argc], &file_stat) == -1)
        fprintf(stderr, "%s\n", strerror(errno));
      else
        {
          fprintf(stdout, "Links\tUid\tGid\tSize\tName\n");
          fprintf(stdout, "%u\t%u\t%u\t%u\t%s\n", file_stat.st_nlink,
                  file_stat.st_uid, file_stat.st_gid, file_stat.st_size,
                  argv[argc]);
        }
    }
  return 0;
}

Put the source in a file (main.c) and compile this:

 gcc main.c -o test

Now, to run type:

 ./test main.c
 ./test *

ReferencesEdit