DIRECTORY(3) Library Functions Manual DIRECTORY(3)

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 () interface is deprecated because it cannot be used correctly unless {NAME_MAX} is a fixed value.

The () 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 () function is equivalent to the opendir() function except that the directory is specified by a file descriptor fd rather than by a name.

Upon successful return from (), 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 () 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. Note that the order of the directory entries vended by readdir() is not specified. Some filesystems may return entries in lexicographic sort order and others may not. Also note that not all filesystems will provide a value for d_type and may instead set the field to DT_UNKNOWN.

The () 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 () 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 () 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 () function resets the position of the named directory stream to the beginning of the directory.

The () 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 () function is equivalent to the closedir() function except that this function returns directory file descriptor instead of closing it.

The () 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:

[]
Search permission is denied for the component of the path prefix of filename or read permission is denied for filename.
[]
A loop exists in symbolic links encountered during resolution of the filename argument.
[]
The length of the filename argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.
[]
A component of filename does not name an existing directory or filename is an empty string.
[]
A component of filename is not a directory.

The fdopendir() function will fail if:

[]
The fd argument is not a valid file descriptor open for reading.
[]
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).

close(2), lseek(2), open(2), read(2), dir(5)

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.

August 1, 2020 Mac OS X 13