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

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.

NAME
       readdir, readdir_r — read a directory

SYNOPSIS
       #include <dirent.h>

       struct dirent *readdir(DIR *dirp);
       int readdir_r(DIR *restrict dirp, struct dirent *restrict entry,
	   struct dirent **restrict result);

DESCRIPTION
       The type DIR, which is defined in the <dirent.h> header,	 represents  a
       directory  stream,  which  is  an ordered sequence of all the directory
       entries in a particular directory. Directory entries  represent	files;
       files  may  be  removed	from a directory or added to a directory asyn‐
       chronously to the operation of readdir().

       The readdir() function shall return a pointer to a structure represent‐
       ing the directory entry at the current position in the directory stream
       specified by the argument dirp, and position the	 directory  stream  at
       the next entry. It shall return a null pointer upon reaching the end of
       the directory stream. The structure dirent defined  in  the  <dirent.h>
       header  describes a directory entry. The value of the structure's d_ino
       member shall be set to the file serial number of the file named by  the
       d_name member. If the d_name member names a symbolic link, the value of
       the d_ino member shall be set to the file serial number of the symbolic
       link itself.

       The  readdir()  function	 shall not return directory entries containing
       empty names. If entries for dot or dot-dot exist, one  entry  shall  be
       returned	 for  dot  and one entry shall be returned for dot-dot; other‐
       wise, they shall not be returned.

       The application shall not modify the  structure	to  which  the	return
       value of readdir() points, nor any storage areas pointed to by pointers
       within the structure. The returned pointer,  and	 pointers  within  the
       structure,  might  be invalidated or the structure or the storage areas
       might be overwritten by a subsequent call  to  readdir()	 on  the  same
       directory  stream. They shall not be affected by a 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() or rewinddir(), whether a subsequent call to
       readdir() returns an entry for that file is unspecified.

       The readdir() function may buffer several directory entries per	actual
       read  operation;	 readdir()  shall mark for update the last data access
       timestamp of the directory each time the directory is actually read.

       After a call to fork(), either the parent or child (but not  both)  may
       continue	 processing the directory stream using readdir(), rewinddir(),
       or seekdir().  If both the parent and child processes use  these	 func‐
       tions, the result is undefined.

       The readdir() function need not be thread-safe.

       Applications  wishing to check for error situations should set errno to
       0 before calling readdir().  If errno is set to non-zero on return,  an
       error occurred.

       The  readdir_r()	 function shall initialize the dirent structure refer‐
       enced by entry to represent the directory entry at the current position
       in  the	directory  stream referred to by dirp, store a pointer to this
       structure at the location referenced by result, and position the direc‐
       tory stream at the next entry.

       The storage pointed to by entry shall be large enough for a dirent with
       an array of char d_name members containing at least  {NAME_MAX}+1  ele‐
       ments.

       Upon  successful return, the pointer returned at *result shall have the
       same value as the argument entry.  Upon reaching the end of the	direc‐
       tory stream, this pointer shall have the value NULL.

       The  readdir_r() function shall not return directory entries containing
       empty names.

       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	 may  buffer  several  directory  entries  per
       actual  read operation; readdir_r() shall mark for update the last data
       access timestamp of the directory each time the directory  is  actually
       read.

RETURN VALUE
       Upon  successful	 completion,  readdir()	 shall	return a pointer to an
       object of type struct dirent.  When an error  is	 encountered,  a  null
       pointer shall be returned and errno shall be set to indicate the error.
       When the end of the directory is encountered, a null pointer  shall  be
       returned and errno is not changed.

       If  successful,	the readdir_r() function shall return zero; otherwise,
       an error number shall be returned to indicate the error.

ERRORS
       These functions shall fail if:

       EOVERFLOW
	      One of the values in the structure to be returned cannot be rep‐
	      resented correctly.

       These 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.

       The following sections are informative.

EXAMPLES
       The following sample program searches the current directory for each of
       the arguments supplied on the command line.

	   #include <dirent.h>
	   #include <errno.h>
	   #include <stdio.h>
	   #include <string.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);
	   }

APPLICATION USAGE
       The readdir() function should be used in	 conjunction  with  opendir(),
       closedir(), and rewinddir() to examine the contents of the directory.

       The  readdir_r()	 function  is thread-safe and shall return values in a
       user-supplied buffer instead of possibly using a static data area  that
       may be overwritten by each call.

RATIONALE
       The returned value of readdir() merely represents a directory entry. No
       equivalence should be inferred.

       Historical  implementations  of	readdir()  obtain  multiple  directory
       entries	on a single read operation, which permits subsequent readdir()
       operations to operate from the buffered information. Any	 wording  that
       required each successful readdir() operation to mark the directory last
       data access timestamp for update would disallow such historical perfor‐
       mance-oriented implementations.

       When returning a directory entry for the root of a mounted file system,
       some historical implementations of readdir() returned the  file	serial
       number  of  the	underlying mount point, rather than of the root of the
       mounted file system. This behavior is considered to be a bug, since the
       underlying file serial number has no significance to applications.

       Since  readdir() returns NULL when it detects an error and when the end
       of the directory is encountered, an application that needs to tell  the
       difference  must set errno to zero before the call and check it if NULL
       is returned.  Since the function must not change errno  in  the	second
       case  and  must	set  it	 to a non-zero value in the first case, a zero
       errno after a call returning NULL  indicates  end-of-directory;	other‐
       wise, an error.

       Routines to deal with this problem more directly were proposed:

	   int derror (dirp)
	   DIR *dirp;

	   void clearderr (dirp)
	   DIR *dirp;

       The  first would indicate whether an error had occurred, and the second
       would clear the error indication. The simpler  method  involving	 errno
       was  adopted  instead by requiring that readdir() not change errno when
       end-of-directory is encountered.

       An error or signal indicating that a directory has changed  while  open
       was considered but rejected.

       The  thread-safe version of the directory reading function returns val‐
       ues in a user-supplied buffer instead of possibly using a  static  data
       area  that  may be overwritten by each call. Either the {NAME_MAX} com‐
       pile-time constant or the corresponding pathconf() option can  be  used
       to determine the maximum sizes of returned pathnames.

FUTURE DIRECTIONS
       None.

SEE ALSO
       closedir(),  dirfd(),  exec,  fdopendir(), fstatat(), rewinddir(), sym‐
       link()

       The Base Definitions volume of POSIX.1‐2008, <dirent.h>, <sys_types.h>

COPYRIGHT
       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 Electri‐
       cal 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.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			   READDIR(3P)
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