| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
READDIR(3) Linux Programmer's Manual READDIR(3)
readdir, readdir_r - read a directory
#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
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; /* offset to the next dirent */
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; 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.
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.
EBADF Invalid directory stream descriptor dirp.
SVr4, 4.3BSD, POSIX.1-2001.
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.
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 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:
len = offsetof(struct dirent, d_name) +
pathconf(dirpath, _PC_NAME_MAX) + 1
entryp = malloc(len);
(POSIX.1 requires that d_name is the last field in a struct dirent.)
getdents(2), read(2), closedir(3), dirfd(3), ftw(3), offsetof(3), opendir(3),
rewinddir(3), scandir(3), seekdir(3), telldir(3)
This page is part of release 3.32 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/.
2010-09-10 READDIR(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface