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This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
Contents
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.
Copyright
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 FDOPENDIR(3POSIX)
Description
The fdopendir() function shall be equivalent to the opendir() function except that the directory is
specified by a file descriptor rather than by a name. The file offset associated with the file descriptor
at the time of the call determines which entries are returned.
Upon successful return from fdopendir(), the file descriptor is under the control of the system, and if
any attempt is made to close the file descriptor, or to modify the state of the associated description,
other than by means of closedir(), readdir(), readdir_r(), rewinddir(), or seekdir(), the behavior is
undefined. Upon calling closedir() the file descriptor shall be closed.
It is unspecified whether the FD_CLOEXEC flag will be set on the file descriptor by a successful call to
fdopendir().
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.
If the type DIR is implemented using a file descriptor, the descriptor shall be obtained as if the
O_DIRECTORY flag was passed to open().
Errors
The fdopendir() function shall fail if:
EBADF The fd argument is not a valid file descriptor open for reading.
ENOTDIR
The descriptor fd is not associated with a directory.
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 a component of a pathname 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 names an existing file that is neither a directory nor a symbolic link to a
directory.
The opendir() function may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the dirname argument.
EMFILE All file descriptors available to the process are currently open.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an
intermediate result with a length that exceeds {PATH_MAX}.
ENFILE Too many files are currently open in the system.
Thefollowingsectionsareinformative.Examples
OpenaDirectoryStream
The following program fragment demonstrates how the opendir() function is used.
#include <dirent.h>
...
DIR *dir;
struct dirent *dp;
...
if ((dir = opendir (".")) == NULL) {
perror ("Cannot open .");
exit (1);
}
while ((dp = readdir (dir)) != NULL) {
...
FindAndOpenaFile
The following program searches through a given directory looking for files whose name does not begin with
a dot and whose size is larger than 1 MiB.
#include <stdio.h>
#include <dirent.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
struct stat statbuf;
DIR *d;
struct dirent *dp;
int dfd, ffd;
if ((d = fdopendir((dfd = open("./tmp", O_RDONLY)))) == NULL) {
fprintf(stderr, "Cannot open ./tmp directory\n");
exit(1);
}
while ((dp = readdir(d)) != NULL) {
if (dp->d_name[0] == '.')
continue;
/* there is a possible race condition here as the file
* could be renamed between the readdir and the open */
if ((ffd = openat(dfd, dp->d_name, O_RDONLY)) == -1) {
perror(dp->d_name);
continue;
}
if (fstat(ffd, &statbuf) == 0 && statbuf.st_size > (1024*1024)) {
/* found it ... */
printf("%s: %jdK\n", dp->d_name,
(intmax_t)(statbuf.st_size / 1024));
}
close(ffd);
}
closedir(d); // note this implicitly closes dfd
return 0;
}
Future Directions
None.
Name
fdopendir, opendir — open directory associated with file descriptor
Prolog
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface
may not be implemented on Linux.
Rationale
The purpose of the fdopendir() function is to enable opening files in directories other than the current
working directory without exposure to race conditions. Any part of the path of a file could be changed in
parallel to a call to opendir(), resulting in unspecified behavior.
Based on historical implementations, the rules about file descriptors apply to directory streams as well.
However, this volume of POSIX.1‐2017 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 POSIX.1‐2017 does not provide a
way to test apriori 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 POSIX.1‐2017 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.
Return Value
Upon successful completion, these functions shall return a pointer to an object of type DIR. Otherwise,
these functions shall return a null pointer and set errno to indicate the error.
See Also
closedir(), dirfd(), fstatat(), open(), readdir(), rewinddir(), symlink()
The Base Definitions volume of POSIX.1‐2017, <dirent.h>, <sys_types.h>Synopsis
#include <dirent.h>
DIR *fdopendir(int fd);
DIR *opendir(const char *dirname);
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