READDIR(3) Linux Programmers Manual READDIR(3)
NAME
readdir, readdir_r - read a directory
SYNOPSIS
#include
struct dirent *readdir(DIR *dir);
int readdir_r(DIR *dir, struct dirent *entry, struct dirent **result);
DESCRIPTION
The readdir() function returns a pointer to a dirent structure repre
senting the next directory entry in the directory stream pointed to by
dir. 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 */
char d_name[256]; /* filename */
};
According to POSIX, the dirent structure contains a field char d_name[]
of unspecified size, with at most NAME_MAX characters preceding the
terminating null byte. POSIX.1-2001 also documents the field ino_t
d_ino as an XSI extension. 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 dir, 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 encoun
tered, then NULL is instead returned in *result.
RETURN VALUE
The readdir() function returns a pointer to a dirent structure, or NULL
if an error occurs or end of the directory stream is reached. On
error, errno is set appropriately.
The readdir_r() function returns 0 on success. On error, it returns a
positive error number. If the end of the directory stream is reached,
readdir_r() returns 0, and returns NULL in *result.
ERRORS
EBADF Invalid directory stream descriptor dir.
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.
Other than Linux, the d_type field is available mainly only on BSD sys
tems. This field makes it possible to avoid the expense of calling
stat(2) if further actions depend on the type of the file. If the
_BSD_SOURCE feature test macro is defined, then glibc defines the fol
lowing 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.
Since POSIX.1 does not specify the size of the d_name field, and other
non-standard 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.)
SEE ALSO
read(2), closedir(3), dirfd(3), ftw(3), offsetof(3), opendir(3),
rewinddir(3), scandir(3), seekdir(3), telldir(3), fea
ture_test_macros(7)
COLOPHON
This page is part of release 3.05 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/.
2008-07-04 READDIR(3)
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