readdir_r(3)

NAME
readdir_r - read a directory

LIBRARY
Standard C library (libc, -lc)

SYNOPSIS
#include <dirent.h>

[[deprecated]] 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

DESCRIPTION
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 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.

RETURN VALUE
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

EBADF
    Invalid directory stream descriptor dirp.

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

ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value
 | Thread safety | MT-Safe

STANDARDS
POSIX.1-2008.

HISTORY
POSIX.1-2001.

SEE ALSO
readdir(3)