Manpages - readdir_r.3

readdir_r - read a directory

  #include <dirent.h>

  int readdir_r(DIR *restrict dirp, struct dirent *restrict entry,
   struct dirent **restrict result);

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

*readdir_r*():

      _POSIX_C_SOURCE
          || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_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 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 *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 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.

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.

EBADF

Invalid directory stream descriptor dirp.

ENAMETOOLONG

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).

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

*readdir*(3)

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