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NAME

       readdir - read a directory

SYNOPSIS

       #include <dirent.h>

       struct dirent *readdir(DIR *dirp);

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.

       In the  glibc  implementation,  the  dirent  structure  is  defined  as
       follows:

           struct dirent {
               ino_t          d_ino;       /* Inode number */
               off_t          d_off;       /* Not an offset; see below */
               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]; /* Null-terminated filename */
           };

       The  only  fields  in the dirent structure that are mandated by POSIX.1
       are d_name and d_ino.  The other fields  are  unstandardized,  and  not
       present on all systems; see NOTES below for some further details.

       The fields of the dirent structure are as follows:

       d_ino  This is the inode number of the file.

       d_off  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).

       d_reclen
              This  is  the  size (in bytes) of the returned record.  This may
              not match the size of the structure definition shown above;  see
              NOTES.

       d_type This  field contains a value indicating the file type, making it
              possible to avoid the expense of  calling  lstat(2)  if  further
              actions depend on the type of the file.

              When  a  suitable feature test macro is defined (_DEFAULT_SOURCE
              on glibc versions since 2.19, or _BSD_SOURCE on  glibc  versions
              2.19  and  earlier), 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 could not be determined.

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

       d_name This field contains the null terminated filename.  See NOTES.

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

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.  To distinguish end of stream and from an error,
       set errno to zero before calling readdir() and then check the value  of
       errno if NULL is returned.

ERRORS

       EBADF  Invalid directory stream descriptor dirp.

ATTRIBUTES

       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       ┌──────────┬───────────────┬──────────────────────────┐
       │InterfaceAttributeValue                    │
       ├──────────┼───────────────┼──────────────────────────┤
       │readdir() │ Thread safety │ MT-Unsafe race:dirstream │
       └──────────┴───────────────┴──────────────────────────┘

       In the current POSIX.1 specification (POSIX.1-2008), readdir()  is  not
       required   to  be  thread-safe.   However,  in  modern  implementations
       (including the glibc implementation),  concurrent  calls  to  readdir()
       that  specify  different  directory  streams are thread-safe.  In cases
       where multiple threads must read from the same directory stream,  using
       readdir()  with external synchronization is still preferable to the use
       of the deprecated readdir_r(3) function.  It is expected that a  future
       version  of  POSIX.1  will  require  that readdir() be thread-safe when
       concurrently employed on different directory streams.

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

NOTES

       A directory stream is opened using opendir(3).

       The order in which filenames are read by successive calls to  readdir()
       depends on the filesystem implementation; it us unlikely that the names
       will be sorted in any fashion.

       Only the fields d_name and (as an XSI extension) d_ino are specified in
       POSIX.1.   Other  than Linux, the d_type field is available mainly only
       on BSD systems.  The remaining fields are available on  many,  but  not
       all  systems.   Under glibc, programs can check for the availability 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 d_name field
       The dirent structure definition shown above is  taken  from  the  glibc
       headers, and shows the d_name field with a fixed size.

       Warning:  applications  should  avoid any dependence on the size of the
       d_name field.  POSIX defines it as char d_name[], a character array  of
       unspecified  size,  with  at  most  NAME_MAX  characters  preceding the
       terminating null byte ('\0').

       POSIX.1 explicitly notes that this field  should  not  be  used  as  an
       lvalue.   The  standard  also  notes  that the use of sizeof(d_name) is
       incorrect; use strlen(d_name) instead.  (On some systems, this field is
       defined  as  char d_name[1]!)   By  implication,  the use sizeof(struct
       dirent) to capture the size of the record including the size of  d_name
       is also incorrect.

       Note that while the call

           fpathconf(fd, _PC_NAME_MAX)

       returns  the value 255 for most filesystems, on some filesystems (e.g.,
       CIFS, Windows  SMB  servers),  the  null-terminated  filename  that  is
       (correctly)  returned in d_name can actually exceed this size.  In such
       cases, the d_reclen field will contain a value that exceeds the size of
       the glibc dirent structure shown above.

SEE ALSO

       getdents(2),   read(2),  closedir(3),  dirfd(3),  ftw(3),  offsetof(3),
       opendir(3),   readdir_r(3),   rewinddir(3),   scandir(3),   seekdir(3),
       telldir(3)

COLOPHON

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       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       https://www.kernel.org/doc/man-pages/.

                                  2016-03-15                        READDIR(3)