1READDIR(3) Linux Programmer's Manual READDIR(3)
2
6 readdir, readdir_r - read a directory
7
9 #include <dirent.h>
10 struct dirent *readdir(DIR *dirp);
12 int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result);
14 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
16 readdir_r():
18 _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _BSD_SOURCE ||
19 _SVID_SOURCE || _POSIX_SOURCE
20
22 The readdir() function returns a pointer to a dirent structure repre‐
23 senting the next directory entry in the directory stream pointed to by
24 dirp. It returns NULL on reaching the end of the directory stream or
25 if an error occurred.
26 On Linux, the dirent structure is defined as follows:
28 struct dirent {
30 ino_t d_ino; /* inode number */
31 off_t d_off; /* not an offset; see NOTES */
32 unsigned short d_reclen; /* length of this record */
33 unsigned char d_type; /* type of file; not supported
34 by all file system types */
35 char d_name[256]; /* filename */
36 };
37 The only fields in the dirent structure that are mandated by POSIX.1
39 are: d_name[], of unspecified size, with at most NAME_MAX characters
40 preceding the terminating null byte ('\0'); and (as an XSI extension)
41 d_ino. The other fields are unstandardized, and not present on all
42 systems; see NOTES below for some further details.
43 The data returned by readdir() may be overwritten by subsequent calls
45 to readdir() for the same directory stream.
46 The readdir_r() function is a reentrant version of readdir(). It reads
48 the next directory entry from the directory stream dirp, and returns it
49 in the caller-allocated buffer pointed to by entry. (See NOTES for
50 information on allocating this buffer.) A pointer to the returned item
51 is placed in *result; if the end of the directory stream was encoun‐
52 tered, then NULL is instead returned in *result.
53
55 On success, readdir() returns a pointer to a dirent structure. (This
56 structure may be statically allocated; do not attempt to free(3) it.)
57 If the end of the directory stream is reached, NULL is returned and
58 errno is not changed. If an error occurs, NULL is returned and errno
59 is set appropriately.
60 The readdir_r() function returns 0 on success. On error, it returns a
62 positive error number (listed under ERRORS). If the end of the direc‐
63 tory stream is reached, readdir_r() returns 0, and returns NULL in
64 *result.
65
67 EBADF Invalid directory stream descriptor dirp.
68
70 Multithreading (see pthreads(7))
71 The readdir() function is not thread-safe.
72 The readdir_r() function is thread-safe.
74
76 SVr4, 4.3BSD, POSIX.1-2001.
77
79 Only the fields d_name and d_ino are specified in POSIX.1-2001. The
80 remaining fields are available on many, but not all systems. Under
81 glibc, programs can check for the availability of the fields not
82 defined in POSIX.1 by testing whether the macros _DIRENT_HAVE_D_NAMLEN,
83 _DIRENT_HAVE_D_RECLEN, _DIRENT_HAVE_D_OFF, or _DIRENT_HAVE_D_TYPE are
84 defined.
85 The value returned in d_off is the same as would be returned by calling
87 telldir(3) at the current position in the directory stream. Be aware
88 that despite its type and name, the d_off field is seldom any kind of
89 directory offset on modern file systems. Applications should treat
90 this field as an opaque value, making no assumptions about its con‐
91 tents; see also telldir(3).
92 Other than Linux, the d_type field is available mainly only on BSD sys‐
94 tems. This field makes it possible to avoid the expense of calling
95 lstat(2) if further actions depend on the type of the file. If the
96 _BSD_SOURCE feature test macro is defined, then glibc defines the fol‐
97 lowing macro constants for the value returned in d_type:
98 DT_BLK This is a block device.
100 DT_CHR This is a character device.
102 DT_DIR This is a directory.
104 DT_FIFO This is a named pipe (FIFO).
106 DT_LNK This is a symbolic link.
108 DT_REG This is a regular file.
110 DT_SOCK This is a UNIX domain socket.
112 DT_UNKNOWN The file type is unknown.
114 If the file type could not be determined, the value DT_UNKNOWN is
116 returned in d_type.
117 Currently, only some file systems (among them: Btrfs, ext2, ext3, and
119 ext4) have full support for returning the file type in d_type. All
120 applications must properly handle a return of DT_UNKNOWN.
121 Since POSIX.1 does not specify the size of the d_name field, and other
123 nonstandard fields may precede that field within the dirent structure,
124 portable applications that use readdir_r() should allocate the buffer
125 whose address is passed in entry as follows:
126 name_max = pathconf(dirpath, _PC_NAME_MAX);
128 if (name_max == -1) /* Limit not defined, or error */
129 name_max = 255; /* Take a guess */
130 len = offsetof(struct dirent, d_name) + name_max + 1;
131 entryp = malloc(len);
132 (POSIX.1 requires that d_name is the last field in a struct dirent.)
134
136 getdents(2), read(2), closedir(3), dirfd(3), ftw(3), offsetof(3),
137 opendir(3), rewinddir(3), scandir(3), seekdir(3), telldir(3)
138
140 This page is part of release 3.53 of the Linux man-pages project. A
141 description of the project, and information about reporting bugs, can
142 be found at http://www.kernel.org/doc/man-pages/.
143 2013-06-21 READDIR(3)