fstat

Name

stat, lstat, fstat, __xstat,__lxstat
- get file status

Library

libc.lib

Synopsis

#include <sys/types.h>

#include <sys/stat.h>

int stat (const char *path, struct stat *sb);

int lstat (const char *path, struct stat *sb);

int fstat (int fd, struct stat *sb);

int __xstat (int version, const char *path, struct stat *sb);

int __lxstat (int version, const char *path, struct stat *sb);

Return values

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

Detailed description

The stat system call obtains information about the file pointed to by path. Read, write or execute permission of the named file is not required, but all directories listed in the path name leading to the file must be searchable.

The lstat system call is like stat except in the case where the named file is a symbolic link, in which case lstat returns information about the link, while stat returns information about the file the link references.

The fstat system call obtains the same information about an open file known by the file descriptor fd.

The __xstat and __lxstat system calls are exactly similar to stat and lstat functionality.

The sb argument is a pointer to a stat structure as defined by

#include <sys/stat.h>and into which information is placed concerning the file.

The fields of struct stat related to the file system are as follows:

st_dev	The numeric ID of the device containing the file.
st_ino	The file’s inode number.
st_nlink
	The number of hard links to the file.

The st_dev and st_ino fields together identify the file uniquely within the system.

The time-related fields of struct stat are as follows:

st_atime	Time when file data last accessed. Changed by the utimes, read and readv system calls.
st_mtime	Time when file data last modified. Changed by the mkdir, mkfifo, utimes, write and writev system calls.
st_ctime	Time when file status was last changed (inode data modification). Changed by the chmod, chown, creat, link, mkdir, mkfifo, rename, rmdir, symlink, truncate, unlink, utimes, write and writev system calls.
st_birthtime
	Time when the inode was created.

If _POSIX_SOURCE is not defined, the time-related fields are defined as:

#ifndef _POSIX_SOURCE
#define st_atime st_atimespec.tv_sec
#define st_mtime st_mtimespec.tv_sec
#define st_ctime st_ctimespec.tv_sec
#endif

The size-related fields of the struct stat are as follows:

st_size	The file size in bytes.
st_blksize
	The optimal I/O block size for the file.
st_blocks	The actual number of blocks allocated for the file in 512-byte units. As short symbolic links are stored in the inode, this number may be zero.

The access-related fields of struct stat are as follows:

st_uid	The user ID of the file’s owner.
st_gid	The group ID of the file.
st_mode
	Status of the file (see below).

The status information word st_mode has the following bits:

#define S_IFMT   0170000  /* type of file */
#define S_IFIFO  0010000  /* named pipe (fifo) */
#define S_IFCHR  0020000  /* character special */
#define S_IFDIR  0040000  /* directory */
#define S_IFBLK  0060000  /* block special */
#define S_IFREG  0100000  /* regular */
#define S_IFLNK  0120000  /* symbolic link */
#define S_IFSOCK 0140000  /* socket */
#define S_IFWHT  0160000  /* whiteout */
#define S_ISUID  0004000  /* set user id on execution */
#define S_ISGID  0002000  /* set group id on execution */
#define S_ISVTX  0001000  /* save swapped text even after use */
#define S_IRUSR  0000400  /* read permission, owner */
#define S_IWUSR  0000200  /* write permission, owner */
#define S_IXUSR  0000100  /* execute/search permission, owner */

For a list of access modes, see

#include <sys/stat.h,> access and chmod The following macros are available to test whether a st_mode value passed in the m argument corresponds to a file of the specified type:

S_ISBLK (m);

Test for a block special file.

S_ISCHR (m);

Test for a character special file.

S_ISDIR (m);

Test for a directory.

S_ISFIFO (m);

Test for a pipe or FIFO special file.

S_ISLNK (m);

Test for a symbolic link. NOTE: Inode structure is not supported by symbian and hence link count updation is not possible. Check for symbolic link would always fail because of this reason.

S_ISREG (m);

Test for a regular file.

S_ISSOCK (m);

Test for a socket.

S_ISWHT (m);

Test for a whiteout.

The macros evaluate to a non-zero value if the test is true or to the value 0 if the test is false.

Limitation: stat and fstat will not give size of directory, here st_size of stat structure is set to zero when stat/fstat call is made on a directory file descriptor. creation time stamp size is not supported by symbian and hence it is set to zero.

Examples

/**
 * Detailed description  : Sample usage of stat system call
 * Preconditions : Example.txt file should be present in working directory
**/
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
int main()
{
  struct stat buf;
   if(stat("Example.txt", &buf) < 0 )
   {
      printf("Failed to stat Example.txt \n");
      return -1;
   }
   printf("Stat system call succeeded \n");
   return 0;
 }
/**
 * Detailed description  : Sample usage of fstat system call
 *
**/
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
int main()
{
  struct stat buf;
   int fd = open("Example.txt" , O_RDONLY | O_CREAT  , 0666);
   if(fstat(fd  , &buf) < 0 ) 
   {
      printf("Failed to stat Example.txt \n");
      return -1;
   }
   printf("Stat system call succeeded \n");
   close(fd);
   return 0;
 }

Output

Stat system call succeeded

Output

Stat system call succeeded

Compatibility

Previous versions of the system used different types for the st_dev, st_uid, st_gid, st_rdev, st_size, st_blksize and st_blocks fields.

Errors

The stat and lstat system calls will fail if:

[`EACCES`]
	Search permission is denied for a component of the path prefix.
[`EFAULT`]
	The sb or path argument points to an invalid address.
[`EIO`]	An I/O error occurred while reading from or writing to the file system.
[`ELOOP`]
	Too many symbolic links were encountered in translating the pathname.
[`ENAMETOOLONG`]
	A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
[`ENOENT`]
	The named file does not exist.
[`ENOTDIR`]
	A component of the path prefix is not a directory.
[`EOVERFLOW`]
	The file size in bytes cannot be represented correctly in the structure pointed to by sb.

The fstat system call will fail if:

[`EBADF`]
	The fd argument is not a valid open file descriptor.
[`EFAULT`]
	The sb argument points to an invalid address.
[`EIO`]	An I/O error occurred while reading from or writing to the file system.
[`EOVERFLOW`]
	The file size in bytes cannot be represented correctly in the structure pointed to by sb.

Bugs

Applying fstat to a socket (and thus to a pipe) returns a zeroed buffer, except for the blocksize field, and a unique device and inode number.

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