trusty (3) opendir.3posix.gz

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 .