Man

Command Section
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).

     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)

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 11.1-RELEASE-p4         August 31, 2016        FreeBSD 11.1-RELEASE-p4
Command Section