NAME
opendir - open a directory
SYNOPSIS
#include <dirent.h>
DIR *opendir(const char *dirname);
DESCRIPTION
The opendir() function shall open a directory stream corresponding to
the directory named by the dirname argument. The directory stream is
positioned at the first entry. If the type DIR is implemented using a
file descriptor, applications shall only be able to open up to a total
of {OPEN_MAX} files and directories.
RETURN VALUE
Upon successful completion, opendir() shall return a pointer to an
object of type DIR. Otherwise, a null pointer shall be returned and
errno set to indicate the error.
ERRORS
The opendir() function shall fail if:
EACCES Search permission is denied for the component of the path prefix
of dirname or read permission is denied for dirname.
ELOOP A loop exists in symbolic links encountered during resolution of
the dirname argument.
ENAMETOOLONG
The length of the dirname argument exceeds {PATH_MAX} or a
pathname component is longer than {NAME_MAX}.
ENOENT A component of dirname does not name an existing directory or
dirname is an empty string.
ENOTDIR
A component of dirname is not a directory.
The opendir() function may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
resolution of the dirname argument.
EMFILE {OPEN_MAX} file descriptors are currently open in the calling
process.
ENAMETOOLONG
As a result of encountering a symbolic link in resolution of the
dirname argument, the length of the substituted pathname string
exceeded {PATH_MAX}.
ENFILE Too many files are currently open in the system.
The following sections are informative.
EXAMPLES
Open a Directory Stream
The following program fragment demonstrates how the opendir() function
is used.
#include <sys/types.h>
#include <dirent.h>
#include <libgen.h>
...
DIR *dir;
struct dirent *dp;
...
if ((dir = opendir (".")) == NULL) {
perror ("Cannot open .");
exit (1);
}
while ((dp = readdir (dir)) != NULL) {
...
APPLICATION USAGE
The opendir() function should be used in conjunction with readdir(),
closedir(), and rewinddir() to examine the contents of the directory
(see the EXAMPLES section in readdir() ). This method is recommended
for portability.
RATIONALE
Based on historical implementations, the rules about file descriptors
apply to directory streams as well. However, this volume of
IEEE Std 1003.1-2001 does not mandate that the directory stream be
implemented using file descriptors. The description of closedir()
clarifies that if a file descriptor is used for the directory stream,
it is mandatory that closedir() deallocate the file descriptor. When a
file descriptor is used to implement the directory stream, it behaves
as if the FD_CLOEXEC had been set for the file descriptor.
The directory entries for dot and dot-dot are optional. This volume of
IEEE Std 1003.1-2001 does not provide a way to test a priori for their
existence because an application that is portable must be written to
look for (and usually ignore) those entries. Writing code that presumes
that they are the first two entries does not always work, as many
implementations permit them to be other than the first two entries,
with a "normal" entry preceding them. There is negligible value in
providing a way to determine what the implementation does because the
code to deal with dot and dot-dot must be written in any case and
because such a flag would add to the list of those flags (which has
proven in itself to be objectionable) and might be abused.
Since the structure and buffer allocation, if any, for directory
operations are defined by the implementation, this volume of
IEEE Std 1003.1-2001 imposes no portability requirements for erroneous
program constructs, erroneous data, or the use of unspecified values
such as the use or referencing of a dirp value or a dirent structure
value after a directory stream has been closed or after a fork() or one
of the exec function calls.
FUTURE DIRECTIONS
None.
SEE ALSO
closedir() , lstat() , readdir() , rewinddir() , symlink() , the Base
Definitions volume of IEEE Std 1003.1-2001, <dirent.h>, <limits.h>,
<sys/types.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .