readdir(3) - Linux manual page (original) (raw)
readdir(3) Library Functions Manual readdir(3)
NAME top
readdir - read a directoryLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <dirent.h>**
**struct dirent *readdir(DIR ***_dirp_**);**DESCRIPTION top
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.
In the glibc implementation, the _dirent_ structure is defined as
follows:
struct dirent {
ino_t d_ino; /* Inode number */
off_t d_off; /* Not an offset; see below */
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]; /* Null-terminated filename */
};
The only fields in the _dirent_ structure that are mandated by
POSIX.1 are _dname_ and _dino_. The other fields are
unstandardized, and not present on all systems; see VERSIONS.
The fields of the _dirent_ structure are as follows:
_dino_ This is the inode number of the file.
_doff_ The value returned in _doff_ is the same as would be
returned by calling [telldir(3)](../man3/telldir.3.html) at the current position in
the directory stream. Be aware that despite its type and
name, the _doff_ 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)](../man3/telldir.3.html).
_dreclen_
This is the size (in bytes) of the returned record. This
may not match the size of the structure definition shown
above; see VERSIONS.
_dtype_ This field contains a value indicating the file type,
making it possible to avoid the expense of calling
[lstat(2)](../man2/lstat.2.html) if further actions depend on the type of the
file.
When a suitable feature test macro is defined
(**_DEFAULT_SOURCE** since glibc 2.19, or **_BSD_SOURCE** on glibc
2.19 and earlier), glibc defines the following macro
constants for the value returned in _dtype_:
**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 could not be determined.
Currently, only some filesystems (among them: Btrfs, ext2,
ext3, and ext4) have full support for returning the file
type in _dtype_. All applications must properly handle a
return of **DT_UNKNOWN**.
_dname_ This field contains the null terminated filename; see
VERSIONS.
The data returned by **readdir**() may be overwritten by subsequent
calls to **readdir**() for the same directory stream.RETURN VALUE top
On success, **readdir**() returns a pointer to a _dirent_ structure.
(This structure may be statically allocated; do not attempt to
[free(3)](../man3/free.3.html) it.)
If the end of the directory stream is reached, NULL is returned
and _[errno](../man3/errno.3.html)_ is not changed. If an error occurs, NULL is returned
and _[errno](../man3/errno.3.html)_ is set to indicate the error. To distinguish end of
stream from an error, set _[errno](../man3/errno.3.html)_ to zero before calling **readdir**()
and then check the value of _[errno](../man3/errno.3.html)_ if NULL is returned.ERRORS top
**EBADF** Invalid directory stream descriptor _dirp_.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌────────────────────┬───────────────┬──────────────────────────┐
│ **Interface** │ **Attribute** │ **Value** │
├────────────────────┼───────────────┼──────────────────────────┤
│ **readdir**() │ Thread safety │ MT-Unsafe race:dirstream │
└────────────────────┴───────────────┴──────────────────────────┘
In the current POSIX.1 specification (POSIX.1-2008), **readdir**() is
not required to be thread-safe. However, in modern
implementations (including the glibc implementation), concurrent
calls to **readdir**() that specify different directory streams are
thread-safe. In cases where multiple threads must read from the
same directory stream, using **readdir**() with external
synchronization is still preferable to the use of the deprecated
[readdir_r(3)](../man3/readdir%5Fr.3.html) function. It is expected that a future version of
POSIX.1 will require that **readdir**() be thread-safe when
concurrently employed on different directory streams.VERSIONS top
Only the fields _dname_ and (as an XSI extension) _dino_ are
specified in POSIX.1. Other than Linux, the _dtype_ field is
available mainly only on BSD systems. 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 d_name field The dirent structure definition shown above is taken from the glibc headers, and shows the dname field with a fixed size.
_Warning_: applications should avoid any dependence on the size of
the _dname_ field. POSIX defines it as _char dname[]_, a character
array of unspecified size, with at most **NAME_MAX** characters
preceding the terminating null byte ('\0').
POSIX.1 explicitly notes that this field should not be used as an
lvalue. The standard also notes that the use of _sizeof(dname)_
is incorrect; use _strlen(dname)_ instead. (On some systems, this
field is defined as _char dname[1]_!) By implication, the use
_sizeof(struct dirent)_ to capture the size of the record including
the size of _dname_ is also incorrect.
Note that while the call
fpathconf(fd, _PC_NAME_MAX)
returns the value 255 for most filesystems, on some filesystems
(e.g., CIFS, Windows SMB servers), the null-terminated filename
that is (correctly) returned in _dname_ can actually exceed this
size. In such cases, the _dreclen_ field will contain a value
that exceeds the size of the glibc _dirent_ structure shown above.STANDARDS top
POSIX.1-2008.HISTORY top
POSIX.1-2001, SVr4, 4.3BSD.NOTES top
A directory stream is opened using [opendir(3)](../man3/opendir.3.html).
The order in which filenames are read by successive calls to
**readdir**() depends on the filesystem implementation; it is
unlikely that the names will be sorted in any fashion.SEE ALSO top
[getdents(2)](../man2/getdents.2.html), [read(2)](../man2/read.2.html), [closedir(3)](../man3/closedir.3.html), [dirfd(3)](../man3/dirfd.3.html), [ftw(3)](../man3/ftw.3.html), [offsetof(3)](../man3/offsetof.3.html),
[opendir(3)](../man3/opendir.3.html), [readdir_r(3)](../man3/readdir%5Fr.3.html), [rewinddir(3)](../man3/rewinddir.3.html), [scandir(3)](../man3/scandir.3.html), [seekdir(3)](../man3/seekdir.3.html),
[telldir(3)](../man3/telldir.3.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.9.1 2024-06-16 readdir(3)
Pages that refer to this page:sshfs(1), fanotify_mark(2), getdents(2), readdir(2), closedir(3), dirfd(3), fts(3), ftw(3), getdirentries(3), glob(3), opendir(3), readdir_r(3), rewinddir(3), scandir(3), seekdir(3), telldir(3), xfs_io(8)