Name
readdir, readdir_r — read a directory
Synopsis
#include <dirent.h>
struct dirent
*readdir( |
DIR *dirp); |
int
readdir_r( |
DIR *dirp, |
| struct dirent *entry, | |
struct dirent **result); |
![[Note]](../stylesheet/note.png) |
Note | ||
|---|---|---|---|
|
DESCRIPTION
The readdir() function
returns a pointer to a dirent
structure representing the next directory entry in the
directory stream pointed to by dirp. It returns NULL on
reaching the end of the directory stream or if an error
occurred.
On Linux, the dirent structure is defined as follows:
struct dirent { ino_t d_ino;off_t d_off;unsigned short d_reclen;unsigned char d_type;
by all filesystem types */char d_name[256];};
The only fields in the dirent structure that are mandated by
POSIX.1 are: d_name[], of unspecified size,
with at most NAME_MAX
characters preceding the terminating null byte ('\0'); and
(as an XSI extension) d_ino. The other fields are
unstandardized, and not present on all systems; see NOTES
below for some further details.
The data returned by readdir() may be overwritten by subsequent
calls to readdir() for the same
directory stream.
The readdir_r() function is
a reentrant version of readdir(). It reads the next directory
entry from the directory stream dirp, and returns it in the
caller-allocated buffer pointed to by entry. (See NOTES for
information on allocating this buffer.) A pointer to the
returned item is placed in *result; if the end of the
directory stream was encountered, then NULL is instead
returned in *result.
RETURN VALUE
On success, readdir()
returns a pointer to a dirent
structure. (This structure may be statically allocated; do
not attempt to free(3) it.) If the end of
the directory stream is reached, NULL is returned and
errno is not changed. If an
error occurs, NULL is returned and errno is set appropriately.
The readdir_r() function
returns 0 on success. On error, it returns a positive error
number (listed under ERRORS). If the end of the directory
stream is reached, readdir_r()
returns 0, and returns NULL in *result.
NOTES
Only the fields d_name and d_ino are specified in
POSIX.1-2001. The remaining fields are available on many, but
not all systems. Under glibc, programs can check for the
availability of the fields not defined in POSIX.1 by testing
whether the macros _DIRENT_HAVE_D_NAMLEN, _DIRENT_HAVE_D_RECLEN, _DIRENT_HAVE_D_OFF, or _DIRENT_HAVE_D_TYPE are defined.
The value returned in d_off is the same as would be
returned by calling telldir(3) at the current
position in the directory stream. Be aware that despite its
type and name, the d_off field is seldom any kind
of directory offset on modern filesystems. Applications
should treat this field as an opaque value, making no
assumptions about its contents; see also telldir(3).
Other than Linux, the d_type field is available
mainly only on BSD systems. This field makes it possible to
avoid the expense of calling lstat(2) if further actions
depend on the type of the file. If the _BSD_SOURCE feature test macro is defined,
then glibc defines the following macro constants for the
value returned in d_type:
DT_BLK-
This is a block device.
DT_CHR-
This is a character device.
DT_DIR-
This is a directory.
DT_FIFO-
This is a named pipe (FIFO).
DT_LNK-
This is a symbolic link.
DT_REG-
This is a regular file.
DT_SOCK-
This is a UNIX domain socket.
DT_UNKNOWN-
The file type is unknown.
If the file type could not be determined, the value
DT_UNKNOWN is returned in
d_type.
Currently, only some filesystems (among them: Btrfs, ext2,
ext3, and ext4) have full support for returning the file type
in d_type. All
applications must properly handle a return of DT_UNKNOWN.
Since POSIX.1 does not specify the size of the d_name field, and other
nonstandard fields may precede that field within the
dirent structure, portable
applications that use readdir_r() should allocate the buffer
whose address is passed in entry as follows:
name_max = pathconf(dirpath, _PC_NAME_MAX); if (name_max == −1) /* Limit not defined, or error */ name_max = 255; /* Take a guess */ len = offsetof(struct dirent, d_name) + name_max + 1; entryp = malloc(len);
(POSIX.1 requires that d_name is the last field in a
struct dirent.)
SEE ALSO
getdents(2), read(2), closedir(3), dirfd(3), ftw(3), offsetof(3), opendir(3), rewinddir(3), scandir(3), seekdir(3), telldir(3)
COLOPHON
This page is part of release 3.54 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man−pages/.
|
Copyright (C) 1993 David Metcalfe (davidprism.demon.co.uk) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END References consulted: Linux libc source code Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) 386BSD man pages Modified Sat Jul 24 16:09:49 1993 by Rik Faith (faithcs.unc.edu) Modified 11 June 1995 by Andries Brouwer (aebcwi.nl) Modified 22 July 1996 by Andries Brouwer (aebcwi.nl) 2007-07-30 Ulrich Drepper <drepperredhat.com>, mtk: Rework discussion of nonstandard structure fields. 2008-09-11, mtk, Document readdir_r(). |