READDIR(3) Linux Programmer's Manual READDIR(3)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);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
readdir_r():
_POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _BSD_SOURCE ||
_SVID_SOURCE || _POSIX_SOURCE
DESCRIPTION
The readdir() function returns a pointer to a dirent structure repre‐
senting 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; /* inode number */
off_t d_off; /* not an offset; see NOTES */
unsigned short d_reclen; /* length of this record */
unsigned char d_type; /* type of file; not supported
by all filesystem types */
char d_name[256]; /* filename */
};
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 encoun‐
tered, 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 direc‐
tory stream is reached, readdir_r() returns 0, and returns NULL in
*result.
ERRORS
EBADF Invalid directory stream descriptor dirp.
ATTRIBUTES
Multithreading (see pthreads(7))
The readdir() function is not thread-safe.
The readdir_r() function is thread-safe.
CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001.
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 sys‐
tems. 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 fol‐
lowing 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 ALSOgetdents(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 3.55 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/.
2013-06-21 READDIR(3)