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Manual Pages  — DIRECTORY

NAME

opendir, fdopendir, readdir, readdir_r, telldir, seekdir, rewinddir, closedir, fdclosedir, dirfd – directory operations

CONTENTS

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).

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);

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_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 BSD 4.2 . 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.

DIRECTORY (3) April 30, 2019

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