1READDIR(3)                 Linux Programmer's Manual                READDIR(3)
2
3
4

NAME

6       readdir - read a directory
7

SYNOPSIS

9       #include <dirent.h>
10
11       struct dirent *readdir(DIR *dirp);
12

DESCRIPTION

14       The  readdir()  function returns a pointer to a dirent structure repre‐
15       senting the next directory entry in the directory stream pointed to  by
16       dirp.   It  returns NULL on reaching the end of the directory stream or
17       if an error occurred.
18
19       In the glibc implementation, the dirent structure is  defined  as  fol‐
20       lows:
21
22           struct dirent {
23               ino_t          d_ino;       /* Inode number */
24               off_t          d_off;       /* Not an offset; see below */
25               unsigned short d_reclen;    /* Length of this record */
26               unsigned char  d_type;      /* Type of file; not supported
27                                              by all filesystem types */
28               char           d_name[256]; /* Null-terminated filename */
29           };
30
31       The  only  fields  in the dirent structure that are mandated by POSIX.1
32       are d_name and d_ino.  The other fields  are  unstandardized,  and  not
33       present on all systems; see NOTES below for some further details.
34
35       The fields of the dirent structure are as follows:
36
37       d_ino  This is the inode number of the file.
38
39       d_off  The  value returned in d_off is the same as would be returned by
40              calling telldir(3) at the  current  position  in  the  directory
41              stream.   Be  aware  that  despite  its type and name, the d_off
42              field is seldom any kind of directory offset on modern  filesys‐
43              tems.   Applications should treat this field as an opaque value,
44              making no assumptions about its contents; see also telldir(3).
45
46       d_reclen
47              This is the size (in bytes) of the returned  record.   This  may
48              not  match the size of the structure definition shown above; see
49              NOTES.
50
51       d_type This field contains a value indicating the file type, making  it
52              possible  to  avoid  the  expense of calling lstat(2) if further
53              actions depend on the type of the file.
54
55              When a suitable feature test macro is  defined  (_DEFAULT_SOURCE
56              on  glibc  versions since 2.19, or _BSD_SOURCE on glibc versions
57              2.19 and earlier), glibc defines the following  macro  constants
58              for the value returned in d_type:
59
60              DT_BLK      This is a block device.
61
62              DT_CHR      This is a character device.
63
64              DT_DIR      This is a directory.
65
66              DT_FIFO     This is a named pipe (FIFO).
67
68              DT_LNK      This is a symbolic link.
69
70              DT_REG      This is a regular file.
71
72              DT_SOCK     This is a UNIX domain socket.
73
74              DT_UNKNOWN  The file type could not be determined.
75
76              Currently, only some filesystems (among them: Btrfs, ext2, ext3,
77              and ext4) have full support  for  returning  the  file  type  in
78              d_type.   All  applications  must  properly  handle  a return of
79              DT_UNKNOWN.
80
81       d_name This field contains the null terminated filename.  See NOTES.
82
83       The data returned by readdir() may be overwritten by  subsequent  calls
84       to readdir() for the same directory stream.
85

RETURN VALUE

87       On  success,  readdir() returns a pointer to a dirent structure.  (This
88       structure may be statically allocated; do not attempt to free(3) it.)
89
90       If the end of the directory stream is reached,  NULL  is  returned  and
91       errno  is  not changed.  If an error occurs, NULL is returned and errno
92       is set appropriately.  To distinguish end of stream and from an  error,
93       set  errno to zero before calling readdir() and then check the value of
94       errno if NULL is returned.
95

ERRORS

97       EBADF  Invalid directory stream descriptor dirp.
98

ATTRIBUTES

100       For  an  explanation  of  the  terms  used   in   this   section,   see
101       attributes(7).
102
103       ┌──────────┬───────────────┬──────────────────────────┐
104Interface Attribute     Value                    
105       ├──────────┼───────────────┼──────────────────────────┤
106readdir() │ Thread safety │ MT-Unsafe race:dirstream │
107       └──────────┴───────────────┴──────────────────────────┘
108
109       In  the  current POSIX.1 specification (POSIX.1-2008), readdir() is not
110       required  to  be  thread-safe.   However,  in  modern   implementations
111       (including  the  glibc  implementation),  concurrent calls to readdir()
112       that specify different directory streams  are  thread-safe.   In  cases
113       where  multiple threads must read from the same directory stream, using
114       readdir() with external synchronization is still preferable to the  use
115       of  the deprecated readdir_r(3) function.  It is expected that a future
116       version of POSIX.1 will require that readdir() be thread-safe when con‐
117       currently employed on different directory streams.
118

CONFORMING TO

120       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
121

NOTES

123       A directory stream is opened using opendir(3).
124
125       The  order in which filenames are read by successive calls to readdir()
126       depends on the filesystem implementation; it is unlikely that the names
127       will be sorted in any fashion.
128
129       Only the fields d_name and (as an XSI extension) d_ino are specified in
130       POSIX.1.  Other than Linux, the d_type field is available  mainly  only
131       on  BSD  systems.   The remaining fields are available on many, but not
132       all systems.  Under glibc, programs can check for the  availability  of
133       the  fields  not  defined  in  POSIX.1  by  testing  whether the macros
134       _DIRENT_HAVE_D_NAMLEN,  _DIRENT_HAVE_D_RECLEN,  _DIRENT_HAVE_D_OFF,  or
135       _DIRENT_HAVE_D_TYPE are defined.
136
137   The d_name field
138       The  dirent  structure  definition  shown above is taken from the glibc
139       headers, and shows the d_name field with a fixed size.
140
141       Warning: applications should avoid any dependence on the  size  of  the
142       d_name  field.  POSIX defines it as char d_name[], a character array of
143       unspecified size, with at most NAME_MAX characters preceding the termi‐
144       nating null byte ('\0').
145
146       POSIX.1  explicitly  notes  that  this  field  should not be used as an
147       lvalue.  The standard also notes that  the  use  of  sizeof(d_name)  is
148       incorrect; use strlen(d_name) instead.  (On some systems, this field is
149       defined as char d_name[1]!)   By  implication,  the  use  sizeof(struct
150       dirent)  to capture the size of the record including the size of d_name
151       is also incorrect.
152
153       Note that while the call
154
155           fpathconf(fd, _PC_NAME_MAX)
156
157       returns the value 255 for most filesystems, on some filesystems  (e.g.,
158       CIFS,  Windows SMB servers), the null-terminated filename that is (cor‐
159       rectly) returned in d_name can actually  exceed  this  size.   In  such
160       cases, the d_reclen field will contain a value that exceeds the size of
161       the glibc dirent structure shown above.
162

SEE ALSO

164       getdents(2),  read(2),  closedir(3),  dirfd(3),  ftw(3),   offsetof(3),
165       opendir(3),   readdir_r(3),   rewinddir(3),   scandir(3),   seekdir(3),
166       telldir(3)
167

COLOPHON

169       This page is part of release 4.15 of the Linux  man-pages  project.   A
170       description  of  the project, information about reporting bugs, and the
171       latest    version    of    this    page,    can     be     found     at
172       https://www.kernel.org/doc/man-pages/.
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176                                  2017-09-15                        READDIR(3)
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