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

       readdir, readdir_r - read a directory

       #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 ||

       The readdir() function returns a pointer to a dirent  structure  repre-
       senting  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.

       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  direc-
       tory  stream  is  reached,  readdir_r()  returns 0, and returns NULL in

       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 |
       |readdir_r() | Thread safety | MT-Safe                  |
       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

       Only the fields d_name and d_ino are specified in POSIX.1.  The remain-
       ing 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,

       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 sys-
       tems.  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  fol-
       lowing 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.)

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

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                                  2015-08-08                        READDIR(3)
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