DIRECTORY(3) FreeBSD Library Functions Manual DIRECTORY(3)
NAME
opendir, fdopendir, readdir, readdir_r, telldir, seekdir, rewinddir,
closedir, fdclosedir, dirfd - directory operations
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#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);
DESCRIPTION
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).
EXAMPLES
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);
ERRORS
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).
SEE ALSO
close(2), lseek(2), open(2), read(2), dir(5)
STANDARDS
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.
HISTORY
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.
BUGS
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.
FreeBSD 13.1-RELEASE-p6 August 1, 2020 FreeBSD 13.1-RELEASE-p6
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