readdir_r - read a directory

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ readdir_r()                                                                 │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

       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  glibc
       2.24, glibc deprecates 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 ENAMETOOLONGafterthefinaldirectoryentryhasbeenread.  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  implementation),  concurrent  calls  to
          readdir(3)  that  specify  different  directory  streams  are  thread-safe.   Therefore,  the  use  of
          readdir_r() is generally unnecessary in multithreaded 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 above.

       •  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.

EBADF  Invalid directory stream descriptor dirp.

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

       POSIX.1-2001.

       Standard C library (libc, -lc)

       readdir_r - read a directory

       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.

readdir(3)

Linux man-pages 6.9.1                              2024-05-02                                       readdir_r(3)

       POSIX.1-2008.

#include<dirent.h>[[deprecated]]intreaddir_r(DIR*restrictdirp,structdirent*restrictentry,structdirent**restrictresult);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       readdir_r():
           _POSIX_C_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE