.\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)

.\" and Copyright (C) 2008, 2016 Michael Kerrisk <mtk.manpages@gmail.com>

.\"

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.\" 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 (faith@cs.unc.edu)

.\" Modified 11 June 1995 by Andries Brouwer (aeb@cwi.nl)

.\" Modified 22 July 1996 by Andries Brouwer (aeb@cwi.nl)

.\" 2007-07-30 Ulrich Drepper <drepper@redhat.com>, mtk:

.\"     Rework discussion of nonstandard structure fields.

.\"

.TH READDIR 3  2017-09-15 "" "Linux Programmer's Manual"

.SH NAME

readdir \- read a directory

.SH SYNOPSIS

.nf

.B #include <dirent.h>

.PP

.BI "struct dirent *readdir(DIR *" dirp );

.fi

.SH DESCRIPTION

The

.BR readdir ()

function returns a pointer to a \fIdirent\fP structure

representing the next directory entry in the directory stream pointed

to by \fIdirp\fP.

It returns NULL on reaching the end of the directory stream or if

an error occurred.

.PP

In the glibc implementation, the

.I dirent

structure is defined as follows:

.PP

.in +4n

.EX

struct dirent {

    ino_t          d_ino;       /* Inode number */

    off_t          d_off;       /* Not an offset; see below */

    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]; /* Null-terminated filename */

};

.EE

.in

.PP

The only fields in the

.I dirent

structure that are mandated by POSIX.1 are

.IR d_name

and

.IR d_ino .

The other fields are unstandardized, and not present on all systems;

see NOTES below for some further details.

.PP

The fields of the

.I dirent

structure are as follows:

.TP

.I d_ino

This is the inode number of the file.

.TP

.I d_off

The value returned in

.I d_off

is the same as would be returned by calling

.BR telldir (3)

at the current position in the directory stream.

Be aware that despite its type and name, the

.I d_off

field is seldom any kind of directory offset on modern filesystems.

.\" https://lwn.net/Articles/544298/

Applications should treat this field as an opaque value,

making no assumptions about its contents; see also

.BR telldir (3).

.TP

.I d_reclen

This is the size (in bytes) of the returned record.

This may not match the size of the structure definition shown above;

see NOTES.

.TP

.I d_type

This field contains a value indicating the file type,

making it possible to avoid the expense of calling

.BR lstat (2)

if further actions depend on the type of the file.

.IP

When a suitable feature test macro is defined

.RB ( _DEFAULT_SOURCE

on glibc versions since 2.19, or

.BR _BSD_SOURCE

on glibc versions 2.19 and earlier),

glibc defines the following macro constants for the value returned in

.IR d_type :

.RS

.TP 12

.B DT_BLK

This is a block device.

.TP

.B DT_CHR

This is a character device.

.TP

.B DT_DIR

This is a directory.

.TP

.B DT_FIFO

This is a named pipe (FIFO).

.TP

.B DT_LNK

This is a symbolic link.

.TP

.B DT_REG

This is a regular file.

.TP

.B DT_SOCK

This is a UNIX domain socket.

.TP

.B DT_UNKNOWN

The file type could not be determined.

.RE

.IP

Currently,

.\" kernel 2.6.27

.\" The same sentence is in getdents.2

only some filesystems (among them: Btrfs, ext2, ext3, and ext4)

have full support for returning the file type in

.IR d_type .

All applications must properly handle a return of

.BR DT_UNKNOWN .

.TP

.I d_name

This field contains the null terminated filename.

.IR "See NOTES" .

.PP

The data returned by

.BR readdir ()

may be overwritten by subsequent calls to

.BR readdir ()

for the same directory stream.

.SH RETURN VALUE

On success,

.BR readdir ()

returns a pointer to a

.I dirent

structure.

(This structure may be statically allocated; do not attempt to

.BR free (3)

it.)

.PP

If the end of the directory stream is reached, NULL is returned and

.I errno

is not changed.

If an error occurs, NULL is returned and

.I errno

is set appropriately.

To distinguish end of stream and from an error, set

.I errno

to zero before calling

.BR readdir ()

and then check the value of

.I errno

if NULL is returned.

.SH ERRORS

.TP

.B EBADF

Invalid directory stream descriptor \fIdirp\fP.

.SH ATTRIBUTES

For an explanation of the terms used in this section, see

.BR attributes (7).

.TS

allbox;

lb lb lb

l l l.

Interface	Attribute	Value

T{

.BR readdir ()

T}	Thread safety	MT-Unsafe race:dirstream

.TE

.sp 1

.PP

In the current POSIX.1 specification (POSIX.1-2008),

.BR readdir ()

is not required to be thread-safe.

However, in modern implementations (including the glibc implementation),

concurrent calls to

.BR readdir ()

that specify different directory streams are thread-safe.

In cases where multiple threads must read from the same directory stream,

using

.BR readdir ()

with external synchronization is still preferable to the use of the deprecated

.BR readdir_r (3)

function.

It is expected that a future version of POSIX.1

.\" FIXME .

.\" http://www.austingroupbugs.net/view.php?id=696

will require that

.BR readdir ()

be thread-safe when concurrently employed on different directory streams.

.SH CONFORMING TO

POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

.SH NOTES

A directory stream is opened using

.BR opendir (3).

.PP

The order in which filenames are read by successive calls to

.BR readdir ()

depends on the filesystem implementation;

it is unlikely that the names will be sorted in any fashion.

.PP

Only the fields

.I d_name

and (as an XSI extension)

.I d_ino

are specified in POSIX.1.

.\" POSIX.1-2001, POSIX.1-2008

Other than Linux, the

.I d_type

field is available mainly only on BSD systems.

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

.BR _DIRENT_HAVE_D_NAMLEN ,

.BR _DIRENT_HAVE_D_RECLEN ,

.BR _DIRENT_HAVE_D_OFF ,

or

.B _DIRENT_HAVE_D_TYPE

are defined.

.\"

.SS The d_name field

The

.I dirent

structure definition shown above is taken from the glibc headers,

and shows the

.I d_name

field with a fixed size.

.PP

.IR Warning :

applications should avoid any dependence on the size of the

.I d_name

field.

POSIX defines it as

.IR "char\ d_name[]",

a character array of unspecified size, with at most

.B NAME_MAX

characters preceding the terminating null byte (\(aq\\0\(aq).

.PP

POSIX.1 explicitly notes that this field should not be used as an lvalue.

The standard also notes that the use of

.I sizeof(d_name)

is incorrect; use

.IR strlen(d_name)

instead.

(On some systems, this field is defined as

.IR char\ d_name[1] !)

By implication, the use

.IR "sizeof(struct dirent)"

to capture the size of the record including the size of

.IR d_name

is also incorrect.

.PP

Note that while the call

.PP

    fpathconf(fd, _PC_NAME_MAX)

.PP

returns the value 255 for most filesystems,

on some filesystems (e.g., CIFS, Windows SMB servers),

the null-terminated filename that is (correctly) returned in

.I d_name

can actually exceed this size.

In such cases, the

.I d_reclen

field will contain a value that exceeds the size of the glibc

.I dirent

structure shown above.

.SH SEE ALSO

.BR getdents (2),

.BR read (2),

.BR closedir (3),

.BR dirfd (3),

.BR ftw (3),

.BR offsetof (3),

.BR opendir (3),

.BR readdir_r (3),

.BR rewinddir (3),

.BR scandir (3),

.BR seekdir (3),

.BR telldir (3)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.