man3/readdir.3

   1 .\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
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  12 .\" Since the Linux kernel and libraries are constantly changing, this
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  20 .\" Formatted or processed versions of this manual, if unaccompanied by
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  22 .\"
  23 .\" References consulted:
  24 .\"     Linux libc source code
  25 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  26 .\"     386BSD man pages
  27 .\" Modified Sat Jul 24 16:09:49 1993 by Rik Faith (faith@cs.unc.edu)
  28 .\" Modified 11 June 1995 by Andries Brouwer (aeb@cwi.nl)
  29 .\" Modified 22 July 1996 by Andries Brouwer (aeb@cwi.nl)
  30 .\" 2007-07-30 Ulrich Drepper <drepper@redhat.com>, mtk:
  31 .\"     Rework discussion of non-standard structure fields.
  32 .\"
  33 .TH READDIR 3  2008-06-20 "" "Linux Programmer's Manual"
  34 .SH NAME
  35 readdir \- read a directory
  36 .SH SYNOPSIS
  37 .nf
  38 .B #include <sys/types.h>
  39 .sp
  40 .B #include <dirent.h>
  41 .sp
  42 .BI "struct dirent *readdir(DIR *" dir );
  43 .fi
  44 .SH DESCRIPTION
  45 The
  46 .BR readdir ()
  47 function returns a pointer to a \fIdirent\fP structure
  48 representing the next directory entry in the directory stream pointed
  49 to by \fIdir\fP.
  50 It returns NULL on reaching the end-of-file or if
  51 an error occurred.
  52 .PP
  53 On Linux, the
  54 .I dirent
  55 structure is defined as follows:
  56 .PP
  57 .in +4n
  58 .nf
  59 struct dirent {
  60     ino_t          d_ino;       /* inode number */
  61     off_t          d_off;       /* offset to the next dirent */
  62     unsigned short d_reclen;    /* length of this record */
  63     unsigned char  d_type;      /* type of file */
  64     char           d_name[256]; /* filename */
  65 };
  66 .fi
  67 .in
  68 .PP
  69 According to POSIX, the
  70 .I dirent
  71 structure contains a field
  72 .I "char d_name[]"
  73 of unspecified size, with at most
  74 .B NAME_MAX
  75 characters preceding the terminating null byte.
  76 POSIX.1-2001 also documents the field
  77 .I "ino_t d_ino"
  78 as an XSI extension.
  79 The other fields are unstandardized, and not present on all systems;
  80 see NOTES below for some further details.
  81 .PP
  82 The data returned by
  83 .BR readdir ()
  84 may be overwritten by subsequent calls to
  85 .BR readdir ()
  86 for the same directory stream.
  87 .SH "RETURN VALUE"
  88 The
  89 .BR readdir ()
  90 function returns a pointer to a
  91 .I dirent
  92 structure, or
  93 NULL if an error occurs or end-of-file is reached.
  94 On error,
  95 .I errno
  96 is set appropriately.
  97 .SH ERRORS
  98 .TP
  99 .B EBADF
 100 Invalid directory stream descriptor \fIdir\fP.
 101 .SH "CONFORMING TO"
 102 SVr4, 4.3BSD, POSIX.1-2001
 103 .SH NOTES
 104 Only the fields
 105 .I d_name
 106 and
 107 .I d_ino
 108 are specified in POSIX.1-2001.
 109 The remaining fields are available on many, but not all systems.
 110 Under glibc,
 111 programs can check for the availability of the fields not defined
 112 in POSIX.1 by testing whether the macros
 113 .BR _DIRENT_HAVE_D_NAMLEN ,
 114 .BR _DIRENT_HAVE_D_RECLEN ,
 115 .BR _DIRENT_HAVE_D_OFF ,
 116 or
 117 .B _DIRENT_HAVE_D_TYPE
 118 are defined.
 119
 120 Other than Linux, the
 121 .I d_type
 122 field is available mainly only on BSD systems.
 123 This field makes it possible to avoid the expense of calling
 124 .BR stat (2)
 125 if further
 126 actions depend on the type of the file.
 127 If the
 128 .B _BSD_SOURCE
 129 feature test macro is defined,
 130 then glibc defines the following macro constants
 131 for the value returned in
 132 .IR d_type :
 133 .TP 12
 134 .B DT_UNKNOWN
 135 The file type is unknown.
 136 .\" The glibc manual says that on some systems this is the only
 137 .\" value returned
 138 .TP
 139 .B DT_REG
 140 This is a regular file.
 141 .TP
 142 .B DT_LNK
 143 This is a symbolic link.
 144 .TP
 145 .B DT_DIR
 146 This is a directory.
 147 .TP
 148 .B DT_FIFO
 149 This is a named pipe, or FIFO.
 150 .TP
 151 .B DT_SOCK
 152 This is a Unix domain socket.
 153 .TP
 154 .B DT_CHR
 155 This is a character device.
 156 .TP
 157 .B DT_BLK
 158 This is a block device.
 159 .PP
 160 If the file type could not be determined, the value
 161 .B DT_UNKNOWN
 162 is returned in
 163 .IR d_type .
 164 .SH "SEE ALSO"
 165 .BR read (2),
 166 .BR closedir (3),
 167 .BR dirfd (3),
 168 .BR ftw (3),
 169 .BR opendir (3),
 170 .BR rewinddir (3),
 171 .BR scandir (3),
 172 .BR seekdir (3),
 173 .BR telldir (3),
 174 .BR feature_test_macros (7)