readdir(3) — Linux manual page


readdir(3)              Library Functions Manual              readdir(3)

NAME         top

       readdir - read a directory

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <dirent.h>

       struct dirent *readdir(DIR *dirp);

DESCRIPTION         top

       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

           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).

              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

              When a suitable feature test macro is defined
              (_DEFAULT_SOURCE since glibc 2.19, or _BSD_SOURCE on glibc
              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.

                     This is a named pipe (FIFO).

              DT_LNK This is a symbolic link.

              DT_REG This is a regular file.

                     This is a UNIX domain socket.

                     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

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

RETURN VALUE         top

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

ERRORS         top

       EBADF  Invalid directory stream descriptor dirp.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface          Attribute     Value                    │
       │ 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.

VERSIONS         top

       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,
       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.

STANDARDS         top


HISTORY         top

       POSIX.1-2001, SVr4, 4.3BSD.

NOTES         top

       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 is
       unlikely that the names will be sorted in any fashion.

SEE ALSO         top

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

Linux man-pages (unreleased)     (date)                       readdir(3)

Pages that refer to this page: sshfs(1)fanotify_mark(2)getdents(2)readdir(2)closedir(3)dirfd(3)fts(3)ftw(3)getdirentries(3)glob(3)opendir(3)readdir_r(3)rewinddir(3)scandir(3)seekdir(3)telldir(3)xfs_io(8)