opendir
, fdopendir
,
readdir
, readdir_r
,
telldir
, seekdir
,
rewinddir
, closedir
,
fdclosedir
, dirfd
—
directory operations
Standard C Library (libc, -lc)
#include <dirent.h>
DIR *
opendir
(const
char *filename);
DIR *
fdopendir
(int
fd);
struct dirent *
readdir
(DIR
*dirp);
int
readdir_r
(DIR
*dirp, struct dirent
*entry, struct dirent
**result);
long
telldir
(DIR
*dirp);
void
seekdir
(DIR
*dirp, long
loc);
void
rewinddir
(DIR
*dirp);
int
closedir
(DIR
*dirp);
int
fdclosedir
(DIR
*dirp);
int
dirfd
(DIR
*dirp);
The readdir_r
() interface is
deprecated because it cannot be used correctly unless
{NAME_MAX} is a fixed value.
The opendir
() function opens the directory
named by filename, associates a
directory stream with it and returns a pointer to be used
to identify the directory stream in subsequent operations.
The pointer NULL
is returned if
filename cannot be accessed, or if it cannot
malloc(3)
enough memory to hold the whole thing.
The fdopendir
() function is equivalent to
the opendir
() function except that the directory is
specified by a file descriptor fd rather than by a
name. The file offset associated with the file descriptor at the time of the
call determines which entries are returned.
Upon successful return from fdopendir
(),
the file descriptor is under the control of the system, and if any attempt
is made to close the file descriptor, or to modify the state of the
associated description other than by means of
closedir
(), readdir
(),
readdir_r
(), or rewinddir
(),
the behavior is undefined. Upon calling closedir
()
the file descriptor is closed. The FD_CLOEXEC
flag
is set on the file descriptor by a successful call to
fdopendir
().
The readdir
() function returns a pointer
to the next directory entry. The directory entry remains valid until the
next call to readdir
() or
closedir
() on the same directory
stream. The function returns NULL
upon reaching
the end of the directory or on error. In the event of an error,
errno may be set to any of the values documented for
the
getdirentries(2)
system call.
The readdir_r
() function provides the same
functionality as readdir
(), but the caller must
provide a directory entry buffer to store the results
in. The buffer must be large enough for a struct
dirent with a d_name array with
{NAME_MAX} + 1 elements. If the read succeeds,
result is pointed at the entry;
upon reaching the end of the directory result is set
to NULL
. The readdir_r
()
function returns 0 on success or an error number to indicate failure.
The telldir
() function returns a token
representing the current location associated with the named
directory stream. Values returned by
telldir
() are good only for the lifetime of the
DIR
pointer, dirp, from which
they are derived. If the directory is closed and then reopened, prior values
returned by telldir
() will no longer be valid.
Values returned by telldir
() are also invalidated by
a call to rewinddir
().
The seekdir
() function sets the position
of the next readdir
() operation on the
directory stream. The new position reverts to the one
associated with the directory stream when the
telldir
() operation was performed.
The rewinddir
() function resets the
position of the named directory stream to the beginning of
the directory.
The closedir
() function closes the named
directory stream and frees the structure associated with
the dirp pointer, returning 0 on success. On failure,
-1 is returned and the global variable errno is set to
indicate the error.
The fdclosedir
() function is equivalent to
the closedir
() function except that this function
returns directory file descriptor instead of closing it.
The dirfd
() function returns the integer
file descriptor associated with the named directory
stream, see
open(2).
Sample code which searches a directory for entry ``name'' is:
dirp = opendir(".");
if (dirp == NULL)
return (ERROR);
len = strlen(name);
while ((dp = readdir(dirp)) != NULL) {
if (dp->d_namlen == len && strcmp(dp->d_name, name) == 0) {
(void)closedir(dirp);
return (FOUND);
}
}
(void)closedir(dirp);
return (NOT_FOUND);
The opendir
() function will fail if:
- [
EACCES
]
- Search permission is denied for the component of the path prefix of
filename or read permission is denied for
filename.
- [
ELOOP
]
- A loop exists in symbolic links encountered during resolution of the
filename argument.
- [
ENAMETOOLONG
]
- The length of the filename argument exceeds
{
PATH_MAX
} or a pathname component is longer than
{NAME_MAX
}.
- [
ENOENT
]
- A component of filename does not name an existing
directory or filename is an empty string.
- [
ENOTDIR
]
- A component of filename is not a directory.
The fdopendir
() function will fail if:
- [
EBADF
]
- The fd argument is not a valid file descriptor open
for reading.
- [
ENOTDIR
]
- The descriptor fd is not associated with a
directory.
The readdir
() and
readdir_r
() functions may also fail and set
errno for any of the errors specified for the routine
getdents(2).
The telldir
() function may also fail and
set errno for any of the errors specified for the
routine
realloc(3).
The closedir
() function may also fail and
set errno for any of the errors specified for the
routine
close(2).
The closedir
(), dirfd
(),
fdopendir
(), opendir
(),
readdir
(), readdir_r
(),
rewinddir
(), seekdir
() and
telldir
() functions are expected to conform to
IEEE Std 1003.1-2008 (“POSIX.1”). The
fdclosedir
() function and the
d_off, d_reclen and
d_type fields of struct dirent are
non-standard, and should not be used in portable programs.
The opendir
(), readdir
(),
telldir
(), seekdir
(),
rewinddir
(), closedir
(), and
dirfd
() functions appeared in
4.2BSD. The fdopendir
()
function appeared in FreeBSD 8.0.
fdclosedir
() function appeared in
FreeBSD 10.0.
The behaviour of telldir
() and
seekdir
() is likely to be wrong if there are parallel
unlinks happening and the directory is larger than one page. There is code to
ensure that a seekdir
() to the location given by a
telldir
() immediately before the last
readdir
() will always set the correct location to
return the same value as that last readdir
()
performed. This is enough for some applications which want to "push back
the last entry read", e.g., Samba. Seeks back to any other location,
other than the beginning of the directory, may result in unexpected behaviour
if deletes are present. It is hoped that this situation will be resolved with
changes to getdirentries
() and the VFS.