1readdir(3) Library Functions Manual readdir(3)
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6 readdir - read a directory
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9 Standard C library (libc, -lc)
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12 #include <dirent.h>
13 struct dirent *readdir(DIR *dirp);
15
17 The readdir() function returns a pointer to a dirent structure repre‐
18 senting the next directory entry in the directory stream pointed to by
19 dirp. It returns NULL on reaching the end of the directory stream or
20 if an error occurred.
21 In the glibc implementation, the dirent structure is defined as fol‐
23 lows:
24 struct dirent {
26 ino_t d_ino; /* Inode number */
27 off_t d_off; /* Not an offset; see below */
28 unsigned short d_reclen; /* Length of this record */
29 unsigned char d_type; /* Type of file; not supported
30 by all filesystem types */
31 char d_name[256]; /* Null-terminated filename */
32 };
33 The only fields in the dirent structure that are mandated by POSIX.1
35 are d_name and d_ino. The other fields are unstandardized, and not
36 present on all systems; see NOTES below for some further details.
37 The fields of the dirent structure are as follows:
39 d_ino This is the inode number of the file.
41 d_off The value returned in d_off is the same as would be returned by
43 calling telldir(3) at the current position in the directory
44 stream. Be aware that despite its type and name, the d_off
45 field is seldom any kind of directory offset on modern filesys‐
46 tems. Applications should treat this field as an opaque value,
47 making no assumptions about its contents; see also telldir(3).
48 d_reclen
50 This is the size (in bytes) of the returned record. This may
51 not match the size of the structure definition shown above; see
52 NOTES.
53 d_type This field contains a value indicating the file type, making it
55 possible to avoid the expense of calling lstat(2) if further ac‐
56 tions depend on the type of the file.
57 When a suitable feature test macro is defined (_DEFAULT_SOURCE
59 since glibc 2.19, or _BSD_SOURCE on glibc 2.19 and earlier),
60 glibc defines the following macro constants for the value re‐
61 turned in d_type:
62 DT_BLK This is a block device.
64 DT_CHR This is a character device.
66 DT_DIR This is a directory.
68 DT_FIFO This is a named pipe (FIFO).
70 DT_LNK This is a symbolic link.
72 DT_REG This is a regular file.
74 DT_SOCK This is a UNIX domain socket.
76 DT_UNKNOWN The file type could not be determined.
78 Currently, only some filesystems (among them: Btrfs, ext2, ext3,
80 and ext4) have full support for returning the file type in
81 d_type. All applications must properly handle a return of
82 DT_UNKNOWN.
83 d_name This field contains the null terminated filename. See NOTES.
85 The data returned by readdir() may be overwritten by subsequent calls
87 to readdir() for the same directory stream.
88
90 On success, readdir() returns a pointer to a dirent structure. (This
91 structure may be statically allocated; do not attempt to free(3) it.)
92 If the end of the directory stream is reached, NULL is returned and er‐
94 rno is not changed. If an error occurs, NULL is returned and errno is
95 set to indicate the error. To distinguish end of stream from an error,
96 set errno to zero before calling readdir() and then check the value of
97 errno if NULL is returned.
98
100 EBADF Invalid directory stream descriptor dirp.
101
103 For an explanation of the terms used in this section, see at‐
104 tributes(7).
105 ┌───────────────────────────┬───────────────┬──────────────────────────┐
107 │Interface │ Attribute │ Value │
108 ├───────────────────────────┼───────────────┼──────────────────────────┤
109 │readdir() │ Thread safety │ MT-Unsafe race:dirstream │
110 └───────────────────────────┴───────────────┴──────────────────────────┘
111 In the current POSIX.1 specification (POSIX.1-2008), readdir() is not
113 required to be thread-safe. However, in modern implementations
114 (including the glibc implementation), concurrent calls to readdir()
115 that specify different directory streams are thread-safe. In cases
116 where multiple threads must read from the same directory stream, using
117 readdir() with external synchronization is still preferable to the use
118 of the deprecated readdir_r(3) function. It is expected that a future
119 version of POSIX.1 will require that readdir() be thread-safe when
120 concurrently employed on different directory streams.
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123 Only the fields d_name and (as an XSI extension) d_ino are specified in
124 POSIX.1. Other than Linux, the d_type field is available mainly only
125 on BSD systems. The remaining fields are available on many, but not
126 all systems. Under glibc, programs can check for the availability of
127 the fields not defined in POSIX.1 by testing whether the macros
128 _DIRENT_HAVE_D_NAMLEN, _DIRENT_HAVE_D_RECLEN, _DIRENT_HAVE_D_OFF, or
129 _DIRENT_HAVE_D_TYPE are defined.
130 The d_name field
132 The dirent structure definition shown above is taken from the glibc
133 headers, and shows the d_name field with a fixed size.
134 Warning: applications should avoid any dependence on the size of the
136 d_name field. POSIX defines it as char d_name[], a character array of
137 unspecified size, with at most NAME_MAX characters preceding the
138 terminating null byte ('\0').
139 POSIX.1 explicitly notes that this field should not be used as an
141 lvalue. The standard also notes that the use of sizeof(d_name) is
142 incorrect; use strlen(d_name) instead. (On some systems, this field is
143 defined as char d_name[1]!) By implication, the use sizeof(struct
144 dirent) to capture the size of the record including the size of d_name
145 is also incorrect.
146 Note that while the call
148 fpathconf(fd, _PC_NAME_MAX)
150 returns the value 255 for most filesystems, on some filesystems (e.g.,
152 CIFS, Windows SMB servers), the null-terminated filename that is (cor‐
153 rectly) returned in d_name can actually exceed this size. In such
154 cases, the d_reclen field will contain a value that exceeds the size of
155 the glibc dirent structure shown above.
156
158 POSIX.1-2008.
159
161 POSIX.1-2001, SVr4, 4.3BSD.
162
164 A directory stream is opened using opendir(3).
165 The order in which filenames are read by successive calls to readdir()
167 depends on the filesystem implementation; it is unlikely that the names
168 will be sorted in any fashion.
169
171 getdents(2), read(2), closedir(3), dirfd(3), ftw(3), offsetof(3),
172 opendir(3), readdir_r(3), rewinddir(3), scandir(3), seekdir(3),
173 telldir(3)
174Linux man-pages 6.05 2023-07-20 readdir(3)