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

dirfd - get directory stream file descriptor

#include <sys/types.h>
#include <dirent.h>
int dirfd(DIR *dirp);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
/* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200809L
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

The function dirfd() returns the file descriptor associated with the directory stream dirp.
This file descriptor is the one used internally by the directory stream. As a result, it is useful only for functions which do not depend on or alter the file position, such as fstat(2) and fchdir(2). It will be automatically closed when closedir(3) is called.

On success, a nonnegative file descriptor is returned. On error, -1 is returned, and errno is set to indicate the cause of the error.

POSIX.1-2008 specifies two errors, neither of which is returned by the current implementation.
dirp does not refer to a valid directory stream.
The implementation does not support the association of a file descriptor with a directory.

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

POSIX.1-2008. This function was a BSD extension, present in 4.3BSD-Reno, not in 4.2BSD.

open(2), closedir(3), opendir(3), readdir(3), rewinddir(3), scandir(3), seekdir(3), telldir(3)
2016-03-15 Linux