PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

FDOPENDIR(3P)             POSIX Programmer's Manual            FDOPENDIR(3P)

PROLOG         top

       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.

NAME         top

       fdopendir, opendir — open directory associated with file descriptor

SYNOPSIS         top

       #include <dirent.h>

       DIR *fdopendir(int fd);
       DIR *opendir(const char *dirname);

DESCRIPTION         top

       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().

RETURN VALUE         top

       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.

ERRORS         top

       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.

       The following sections are informative.

EXAMPLES         top

   Open a Directory Stream
       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) {
           ...

   Find And Open a File
       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;
           }

APPLICATION USAGE         top

       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(3p)).  This method is
       recommended for portability.

RATIONALE         top

       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.1‐2008 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.1‐2008 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
       POSIX.1‐2008 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         top

       None.

SEE ALSO         top

       closedir(3p), dirfd(3p), fstatat(3p), open(3p), readdir(3p),
       rewinddir(3p), symlink(3p)

       The Base Definitions volume of POSIX.1‐2008, dirent.h(0p),
       sys_types.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                       FDOPENDIR(3P)

Pages that refer to this page: dirent.h(0p)closedir(3p)dirfd(3p)fstatat(3p)ftw(3p)glob(3p)nftw(3p)open(3p)opendir(3p)readdir(3p)rewinddir(3p)seekdir(3p)symlink(3p)telldir(3p)