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

       readdir - read a directory

       #include <dirent.h>

       struct dirent *readdir(DIR *dirp);

       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

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

       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

       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.

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

       EBADF  Invalid directory stream descriptor dirp.

       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.

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

       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.

       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_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.

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

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

                                  2019-03-06                        READDIR(3)