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NAME
readdir, readdir_r - read a directory
SYNOPSIS
#include <dirent.h>
struct dirent *readdir(DIR *dirp);
int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
readdir_r():
_POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _BSD_SOURCE || _SVID_SOURCE || _POSIX_SOURCE
DESCRIPTION
The readdir() function returns a pointer to a dirent structure representing the next
directory entry in the directory stream pointed to by dirp. It returns NULL on reaching
the end of the directory stream or if an error occurred.
On Linux, the dirent structure is defined as follows:
struct dirent {
ino_t d_ino; /* inode number */
off_t d_off; /* not an offset; see NOTES */
unsigned short d_reclen; /* length of this record */
unsigned char d_type; /* type of file; not supported
by all filesystem types */
char d_name[256]; /* filename */
};
The only fields in the dirent structure that are mandated by POSIX.1 are: d_name[], of
unspecified size, with at most NAME_MAX characters preceding the terminating null byte
('\0'); and (as an XSI extension) d_ino. The other fields are unstandardized, and not
present on all systems; see NOTES below for some further details.
The data returned by readdir() may be overwritten by subsequent calls to readdir() for the
same directory stream.
The readdir_r() function is a reentrant version of readdir(). It reads the next directory
entry from the directory stream dirp, and returns it in the caller-allocated buffer
pointed to by entry. (See NOTES for information on allocating this buffer.) A pointer to
the returned item is placed in *result; if the end of the directory stream was
encountered, then NULL is instead returned in *result.
RETURN VALUE
On success, readdir() returns a pointer to a dirent structure. (This structure may be
statically allocated; do not attempt to free(3) it.) If the end of the directory stream
is reached, NULL is returned and errno is not changed. If an error occurs, NULL is
returned and errno is set appropriately.
The readdir_r() function returns 0 on success. On error, it returns a positive error
number (listed under ERRORS). If the end of the directory stream is reached, readdir_r()
returns 0, and returns NULL in *result.
ERRORS
EBADF Invalid directory stream descriptor dirp.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌────────────┬───────────────┬──────────────────────────┐
│Interface │ Attribute │ Value │
├────────────┼───────────────┼──────────────────────────┤
│readdir() │ Thread safety │ MT-Unsafe race:dirstream │
├────────────┼───────────────┼──────────────────────────┤
│readdir_r() │ Thread safety │ MT-Safe │
└────────────┴───────────────┴──────────────────────────┘
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
NOTES
Only the fields d_name and d_ino are specified in POSIX.1. 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
_DIRENT_HAVE_D_NAMLEN, _DIRENT_HAVE_D_RECLEN, _DIRENT_HAVE_D_OFF, or _DIRENT_HAVE_D_TYPE
are defined.
The value returned in d_off is the same as would be returned by calling telldir(3) at the
current position in the directory stream. Be aware that despite its type and name, the
d_off field is seldom any kind of directory offset on modern filesystems. Applications
should treat this field as an opaque value, making no assumptions about its contents; see
also telldir(3).
Other than Linux, the d_type field is available mainly only on BSD systems. This field
makes it possible to avoid the expense of calling lstat(2) if further actions depend on
the type of the file. If the _BSD_SOURCE feature test macro is defined, then glibc
defines the following macro constants for the value returned in d_type:
DT_BLK This is a block device.
DT_CHR This is a character device.
DT_DIR This is a directory.
DT_FIFO This is a named pipe (FIFO).
DT_LNK This is a symbolic link.
DT_REG This is a regular file.
DT_SOCK This is a UNIX domain socket.
DT_UNKNOWN The file type is unknown.
If the file type could not be determined, the value DT_UNKNOWN is returned in d_type.
Currently, only some filesystems (among them: Btrfs, ext2, ext3, and ext4) have full
support for returning the file type in d_type. All applications must properly handle a
return of DT_UNKNOWN.
Since POSIX.1 does not specify the size of the d_name field, and other nonstandard fields
may precede that field within the dirent structure, portable applications that use
readdir_r() should allocate the buffer whose address is passed in entry as follows:
name_max = pathconf(dirpath, _PC_NAME_MAX);
if (name_max == -1) /* Limit not defined, or error */
name_max = 255; /* Take a guess */
len = offsetof(struct dirent, d_name) + name_max + 1;
entryp = malloc(len);
(POSIX.1 requires that d_name is the last field in a struct dirent.)
SEE ALSO
getdents(2), read(2), closedir(3), dirfd(3), ftw(3), offsetof(3), opendir(3),
rewinddir(3), scandir(3), seekdir(3), telldir(3)
COLOPHON
This page is part of release 4.04 of the Linux man-pages project. A description of the
project, information about reporting bugs, and the latest version of this page, can be
found at http://www.kernel.org/doc/man-pages/.
2015-08-08 READDIR(3)