READDIR(3C)READDIR(3C)NAME
readdir, readdir_r - read directory
SYNOPSIS
#include <sys/types.h>
#include <dirent.h>
struct dirent *readdir(DIR *dirp);
struct dirent *readdir_r(DIR *dirp, struct dirent *entry);
Standard conforming
cc [ flag... ] file... -D_POSIX_PTHREAD_SEMANTICS [ library... ]
int readdir_r(DIR *restrict dirp, struct dirent *restrict entry,
struct dirent **restrict result);
DESCRIPTION
The type DIR, which is defined in the header <dirent.h>, represents a
directory stream, which is an ordered sequence of all the directory
entries in a particular directory. Directory entries represent files.
Files can be removed from a directory or added to a directory asyn‐
chronously to the operation of readdir() and readdir_r().
readdir()
The readdir() function returns a pointer to a structure representing
the directory entry at the current position in the directory stream
specified by the argument dirp, and positions the directory stream at
the next entry. It returns a null pointer upon reaching the end of the
directory stream. The structure dirent defined by the <dirent.h> header
describes a directory entry.
The readdir() function will not return directory entries containing
empty names. If entries for . (dot) or .. (dot-dot) exist, one entry
will be returned for dot and one entry will be returned for dot-dot;
otherwise they will not be returned.
The pointer returned by readdir() points to data that can be overwrit‐
ten by another call to readdir() on the same directory stream. These
data are not overwritten by another call to readdir() on a different
directory stream.
If a file is removed from or added to the directory after the most
recent call to opendir(3C) or rewinddir(3C), whether a subsequent call
to readdir() returns an entry for that file is unspecified.
The readdir() function can buffer several directory entries per actual
read operation. It marks for update the st_atime field of the directory
each time the directory is actually read.
After a call to fork(2), either the parent or child (but not both) can
continue processing the directory stream using readdir(), rewinddir()
or seekdir(3C). If both the parent and child processes use these func‐
tions, the result is undefined.
If the entry names a symbolic link, the value of the d_ino member is
unspecified.
readdir_r()
Unless the end of the directory stream has been reached or an error
occurred, the readdir_r() function initializes the dirent structure
referenced by entry to represent the directory entry at the current
position in the directory stream referred to by dirp, and positions
the directory stream at the next entry.
The caller must allocate storage pointed to by entry to be large enough
for a dirent structure with an array of char d_name member containing
at least NAME_MAX (that is, pathconf(directory, _PC_NAME_MAX)) plus one
elements. (_PC_NAME_MAX is defined in <unistd.h>.)
The readdir_r() function will not return directory entries containing
empty names. It is unspecified whether entries are returned for . (dot)
or .. (dot-dot).
If a file is removed from or added to the directory after the most
recent call to opendir() or rewinddir(), whether a subsequent call to
readdir_r() returns an entry for that file is unspecified.
The readdir_r() function can buffer several directory entries per
actual read operation. It marks for update the st_atime field of the
directory each time the directory is actually read.
The standard-conforming version (see standards(5)) of the readdir_r()
function performs all of the actions described above and sets the
pointer pointed to by result. If a directory entry is returned, the
pointer will be set to the same value as the entry argument; otherwise,
it will be set to NULL.
RETURN VALUES
Upon successful completion, readdir() and the default readdir_r()
return a pointer to an object of type struct dirent. When an error is
encountered, a null pointer is returned and errno is set to indicate
the error. When the end of the directory is encountered, a null pointer
is returned and errno is not changed.
The standard-conforming readdir_r() returns 0 if the end of the direc‐
tory is encountered or a directory entry is stored in the structure
referenced by entry. Otherwise, an error number is returned to indicate
the failure.
ERRORS
The readdir() and readdir_r() functions will fail if:
EOVERFLOW
One of the values in the structure to be returned cannot
be represented correctly.
The readdir() and readdir_r() functions may fail if:
EBADF
The dirp argument does not refer to an open directory stream.
ENOENT
The current position of the directory stream is invalid.
USAGE
The readdir() and readdir_r() functions should be used in conjunction
with opendir(), closedir(), and rewinddir() to examine the contents of
the directory. Since readdir() and the default readdir_r() return a
null pointer both at the end of the directory and on error, an applica‐
tion wanting to check for error situations should set errno to 0 before
calling either of these functions. If errno is set to non-zero on
return, an error occurred.
It is safe to use readdir() in a threaded application, so long as only
one thread reads from the directory stream at any given time. The read‐
dir() function is generally preferred over the readdir_r() function.
The standard-conforming readdir_r() returns the error number if an
error occurred. It returns 0 on success (including reaching the end of
the directory stream).
The readdir() and readdir_r() functions have transitional interfaces
for 64-bit file offsets. See lf64(5).
EXAMPLES
Example 1 Search the current directory for the entry name.
The following sample program will search the current directory for each
of the arguments supplied on the command line:
#include <sys/types.h>
#include <dirent.h>
#include <errno.h>
#include <stdio.h>
#include <strings.h>
static void lookup(const char *arg)
{
DIR *dirp;
struct dirent *dp;
if ((dirp = opendir(".")) == NULL) {
perror("couldn't open '.'");
return;
}
do {
errno = 0;
if ((dp = readdir(dirp)) != NULL) {
if (strcmp(dp->d_name, arg) != 0)
continue;
(void) printf("found %s\n", arg);
(void) closedir(dirp);
return;
}
} while (dp != NULL);
if (errno != 0)
perror("error reading directory");
else
(void) printf("failed to find %s\n", arg);
(void) closedir(dirp);
return;
}
int main(int argc, char *argv[])
{
int i;
for (i = 1; i < argc; i++)
lookup(argv[i]);
return (0);
}
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬─────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────┤
│Interface Stability │ Standard │
├────────────────────┼─────────────────┤
│MT-Level │ See below. │
└────────────────────┴─────────────────┘
The readdir() function is Unsafe. The readdir_r() function is Safe.
SEE ALSOfork(2), lstat(2), symlink(2), Intro(3), closedir(3C), opendir(3C),
rewinddir(3C), scandir(3C), seekdir(3C), attributes(5), lf64(5), stan‐
dards(5)NOTES
When compiling multithreaded programs, see the MULTITHREADED APPLICA‐
TIONS section of Intro(3).
Solaris 2.4 and earlier releases provided a readdir_r() interface as
specified in POSIX.1c Draft 6. The final POSIX.1c standard changed the
interface as described above. Support for the Draft 6 interface is pro‐
vided for compatibility only and might not be supported in future
releases. New applications and libraries should use the standard-con‐
forming interface.
For POSIX.1c-conforming applications, the _POSIX_PTHREAD_SEMANTICS and
_REENTRANT flags are automatically turned on by defining the
_POSIX_C_SOURCE flag with a value >= 199506L.
Jun 26, 2007 READDIR(3C)