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);
 
[Note] Note
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 file system 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

Multithreading (see pthreads(7))

The readdir() function is not thread-safe.

The readdir_r() function is thread-safe.

CONFORMING TO

SVr4, 4.3BSD, POSIX.1-2001.

NOTES

Only the fields d_name and d_ino are specified in POSIX.1-2001. 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 file systems. 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 file systems (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 3.52 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man−pages/.


  Copyright (C) 1993 David Metcalfe (davidprism.demon.co.uk)

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References consulted:
    Linux libc source code
    Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
    386BSD man pages
Modified Sat Jul 24 16:09:49 1993 by Rik Faith (faithcs.unc.edu)
Modified 11 June 1995 by Andries Brouwer (aebcwi.nl)
Modified 22 July 1996 by Andries Brouwer (aebcwi.nl)
2007-07-30 Ulrich Drepper <drepperredhat.com>, mtk:
    Rework discussion of nonstandard structure fields.
2008-09-11, mtk, Document readdir_r().