READDIR_R(3)              (2016-03-01)               READDIR_R(3)

          readdir_r - read a directory

          #include <dirent.h>

          int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result

     Feature Test Macro Requirements for glibc (see

                  || /* Glibc versions <= 2.19: */ _BSD_SOURCE ||

          This function is deprecated; use readdir(3) instead.

          The readdir_r() function was invented as a reentrant version
          of  readdir(3).   It reads the next directory entry from the
          directory  stream  dirp,  and  returns  it  in  the  caller-
          allocated  buffer  pointed  to  by entry. For details of the
          dirent structure, see readdir(3).

          A pointer to the returned buffer is placed  in  *result;  if
          the  end  of the directory stream was encountered, then NULL
          is instead returned in *result.

          It is recommended that applications use  readdir(3)  instead
          of readdir_r().  Furthermore, since version 2.24, glibc dep-
          recates readdir_r().  The reasons are as follows:

          *  On  systems  where   NAME_MAX   is   undefined,   calling
             readdir_r()  may be unsafe because the interface does not
             allow the caller to specify the length of the buffer used
             for the returned directory entry.

          *  On some systems, readdir_r() can't read directory entries
             with  very  long  names.   When  the glibc implementation
             encounters such a name, readdir_r() fails with the  error
             ENAMETOOLONG  after  the  final  directory entry has been
             read. On some other systems,  readdir_r()  may  return  a
             success  status, but the returned d_name field may not be
             null terminated or may be truncated.

          *  In  the  current  POSIX.1  specification  (POSIX.1-2008),
             readdir(3)  is  not required to be thread-safe.  However,
             in modern implementations (including the glibc  implemen-
             tation),  concurrent  calls  to  readdir(3)  that specify

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     READDIR_R(3)              (2016-03-01)               READDIR_R(3)

             different directory streams are thread-safe.   Therefore,
             the use of readdir_r() is generally unnecessary in multi-
             threaded programs.  In cases where multiple threads  must
             read  from  the  same  directory stream, using readdir(3)
             with external synchronization is still preferable to  the
             use  of  readdir_r(), for the reasons given in the points

          *  It is expected that a future version of POSIX.1 will make
             readdir_r()  obsolete,  and  require  that  readdir(3) be
             thread-safe  when  concurrently  employed  on   different
             directory streams.

          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.

               Invalid directory stream descriptor dirp.

               A directory entry whose name was too long  to  be  read
               was encountered.

          For an explanation of the terms used in  this  section,  see
          attributes(7).     allbox;    lb    lb    lb    l    l    l.
          Interface Attribute Value   T{    readdir_r()    T}   Thread
          safety  MT-Safe

          POSIX.1-2001, POSIX.1-2008.


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