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Linux 2.6 - man page for readdir_r (linux section 3)

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READDIR(3)			    Linux Programmer's Manual			       READDIR(3)

NAME
       readdir, readdir_r - read a directory

SYNOPSIS
       #include <dirent.h>

       struct dirent *readdir(DIR *dirp);

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

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       readdir_r():
	   _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _BSD_SOURCE || _SVID_SOURCE || _POSIX_SOURCE

DESCRIPTION
       The  readdir()  function  returns  a  pointer  to a dirent structure representing the next
       directory entry in the directory stream pointed to by dirp.  It returns NULL  on  reaching
       the end of the directory stream or if an error occurred.

       On Linux, the dirent structure is defined as follows:

	   struct dirent {
	       ino_t	      d_ino;	   /* inode number */
	       off_t	      d_off;	   /* not an offset; see NOTES */
	       unsigned short d_reclen;    /* length of this record */
	       unsigned char  d_type;	   /* type of file; not supported
					      by all filesystem types */
	       char	      d_name[256]; /* filename */
	   };

       The  only  fields  in  the dirent structure that are mandated by POSIX.1 are: d_name[], of
       unspecified size, with at most NAME_MAX characters preceding  the  terminating  null  byte
       ('\0');	and  (as  an  XSI extension) d_ino.  The other fields are unstandardized, and not
       present on all systems; see NOTES below for some further details.

       The data returned by readdir() may be overwritten by subsequent calls to readdir() for the
       same directory stream.

       The readdir_r() function is a reentrant version of readdir().  It reads the next directory
       entry from the directory stream dirp,  and  returns  it	in  the  caller-allocated  buffer
       pointed to by entry.  (See NOTES for information on allocating this buffer.)  A pointer to
       the returned item is placed in *result; if the end of the  directory  stream  was  encoun-
       tered, then NULL is instead returned in *result.

RETURN VALUE
       On  success,  readdir()	returns  a pointer to a dirent structure.  (This structure may be
       statically allocated; do not attempt to free(3) it.)  If the end of the	directory  stream
       is  reached,  NULL  is  returned  and  errno  is not changed.  If an error occurs, NULL is
       returned and errno is set appropriately.

       The readdir_r() function returns 0 on success.  On error, it returns a positive error num-
       ber  (listed  under  ERRORS).   If the end of the directory stream is reached, readdir_r()
       returns 0, and returns NULL in *result.

ERRORS
       EBADF  Invalid directory stream descriptor dirp.

ATTRIBUTES
   Multithreading (see pthreads(7))
       The readdir() function is not thread-safe.

       The readdir_r() function is thread-safe.

CONFORMING TO
       SVr4, 4.3BSD, POSIX.1-2001.

NOTES
       Only the fields d_name and d_ino are specified in POSIX.1-2001.	The remaining fields  are
       available  on  many,  but not all systems.  Under glibc, programs can check for the avail-
       ability	of  the  fields  not  defined  in  POSIX.1  by	 testing   whether   the   macros
       _DIRENT_HAVE_D_NAMLEN,  _DIRENT_HAVE_D_RECLEN,  _DIRENT_HAVE_D_OFF, or _DIRENT_HAVE_D_TYPE
       are defined.

       The value returned in d_off is the same as would be returned by calling telldir(3) at  the
       current	position  in  the directory stream.  Be aware that despite its type and name, the
       d_off field is seldom any kind of directory offset on  modern  filesystems.   Applications
       should  treat this field as an opaque value, making no assumptions about its contents; see
       also telldir(3).

       Other than Linux, the d_type field is available mainly only on BSD  systems.   This  field
       makes  it  possible  to avoid the expense of calling lstat(2) if further actions depend on
       the type of the file.  If the _BSD_SOURCE  feature  test  macro	is  defined,  then  glibc
       defines the following macro constants for the value returned in d_type:

       DT_BLK	   This is a block device.

       DT_CHR	   This is a character device.

       DT_DIR	   This is a directory.

       DT_FIFO	   This is a named pipe (FIFO).

       DT_LNK	   This is a symbolic link.

       DT_REG	   This is a regular file.

       DT_SOCK	   This is a UNIX domain socket.

       DT_UNKNOWN  The file type is unknown.

       If the file type could not be determined, the value DT_UNKNOWN is returned in d_type.

       Currently,  only some filesystems (among them: Btrfs, ext2, ext3, and ext4) have full sup-
       port for returning the file type in d_type.   All  applications	must  properly	handle	a
       return of DT_UNKNOWN.

       Since  POSIX.1 does not specify the size of the d_name field, and other nonstandard fields
       may precede that field within the dirent structure, portable applications that  use  read-
       dir_r() should allocate the buffer whose address is passed in entry as follows:

	   name_max = pathconf(dirpath, _PC_NAME_MAX);
	   if (name_max == -1)	       /* Limit not defined, or error */
	       name_max = 255;	       /* Take a guess */
	   len = offsetof(struct dirent, d_name) + name_max + 1;
	   entryp = malloc(len);

       (POSIX.1 requires that d_name is the last field in a struct dirent.)

SEE ALSO
       getdents(2),  read(2),  closedir(3),  dirfd(3),	ftw(3),  offsetof(3), opendir(3), rewind-
       dir(3), scandir(3), seekdir(3), telldir(3)

COLOPHON
       This page is part of release 3.55 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at
       http://www.kernel.org/doc/man-pages/.

					    2013-06-21				       READDIR(3)
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