Document DT_LNK (symbolic link) for d_type field.

[thirdparty/man-pages.git] / man3 / readdir.3

.\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
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.\" the source, must acknowledge the copyright and authors of this work.
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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 non-standard structure fields.
.\"
.TH READDIR 3  2008-06-20 "" "Linux Programmer's Manual"
.SH NAME
readdir \- read a directory
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.sp
.B #include <dirent.h>
.sp
.BI "struct dirent *readdir(DIR *" dir );
.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 \fIdir\fP.
It returns NULL on reaching the end-of-file or if
an error occurred.
.PP
On Linux, the
.I dirent
structure is defined as follows:
.PP
.in +4n
.nf
struct dirent {
    ino_t          d_ino;       /* inode number */
    off_t          d_off;       /* offset to the next dirent */
    unsigned short d_reclen;    /* length of this record */
    unsigned char  d_type;      /* type of file */
    char           d_name[256]; /* filename */
};
.fi
.in
.PP
According to POSIX, the
.I dirent
structure contains a field
.I "char d_name[]"
of unspecified size, with at most
.B NAME_MAX
characters preceding the terminating null byte.
POSIX.1-2001 also documents the field
.I "ino_t d_ino"
as an XSI extension.
The other fields are unstandardized, and not present on all systems;
see NOTES below for some further details.
.PP
The data returned by
.BR readdir ()
may be overwritten by subsequent calls to
.BR readdir ()
for the same directory stream.
.SH "RETURN VALUE"
The
.BR readdir ()
function returns a pointer to a
.I dirent
structure, or
NULL if an error occurs or end-of-file is reached.
On error,
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EBADF
Invalid directory stream descriptor \fIdir\fP.
.SH "CONFORMING TO"
SVr4, 4.3BSD, POSIX.1-2001
.SH NOTES
Only the fields
.I d_name
and
.I 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
.BR _DIRENT_HAVE_D_NAMLEN ,
.BR _DIRENT_HAVE_D_RECLEN ,
.BR _DIRENT_HAVE_D_OFF ,
or
.B _DIRENT_HAVE_D_TYPE
are defined.

Other than Linux, the
.I d_type
field is available mainly only on BSD systems.
This field makes it possible to avoid the expense of calling
.BR stat (2)
if further
actions depend on the type of the file.
If the
.B _BSD_SOURCE
feature test macro is defined,
then glibc defines the following macro constants
for the value returned in
.IR d_type :
.TP 12
.B DT_UNKNOWN
The file type is unknown.
.\" The glibc manual says that on some systems this is the only
.\" value returned
.TP
.B DT_REG
This is a regular file.
.TP
.B DT_LNK
This is a symbolic link.
.TP
.B DT_DIR
This is a directory.
.TP
.B DT_FIFO
This is a named pipe, or FIFO.
.TP
.B DT_SOCK
This is a Unix domain socket.
.TP
.B DT_CHR
This is a character device.
.TP
.B DT_BLK
This is a block device.
.PP
If the file type could not be determined, the value
.B DT_UNKNOWN
is returned in
.IR d_type .
.SH "SEE ALSO"
.BR read (2),
.BR closedir (3),
.BR dirfd (3),
.BR ftw (3),
.BR opendir (3),
.BR rewinddir (3),
.BR scandir (3),
.BR seekdir (3),
.BR telldir (3),
.BR feature_test_macros (7)