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

NAME         top

       readdir, readdir_r - read a directory

SYNOPSIS         top

       #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)):

           _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _BSD_SOURCE ||

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.

       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 encountered, then NULL is instead returned in *result.

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 appropriately.

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

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 │
       │readdir_r() │ Thread safety │ MT-Safe                  │

CONFORMING TO         top

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

NOTES         top

       Only the fields d_name and d_ino are specified in POSIX.1.  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 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 support 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 readdir_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         top

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

COLOPHON         top

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                                 2015-08-08                       READDIR(3)