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   dirfd.3p    ( 3 )

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Пролог (Prolog)

This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

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Имя (Name)

dirfd — extract the file descriptor used by a DIR stream

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Синопсис (Synopsis)

#include <dirent.h>

       int dirfd(DIR *dirp);

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Описание (Description)

The dirfd() function shall return a file descriptor referring to
       the same directory as the dirp argument. This file descriptor
       shall be closed by a call to closedir().  If any attempt is made
       to close the file descriptor, or to modify the state of the
       associated description, other than by means of closedir(),
       readdir(), readdir_r(), rewinddir(), or seekdir(), the behavior
       is undefined.

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Возвращаемое значение (Return value)

Upon successful completion, the dirfd() function shall return an
       integer which contains a file descriptor for the stream pointed
       to by dirp.  Otherwise, it shall return -1 and shall set errno to
       indicate the error.

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Ошибки (Error)

The dirfd() function may fail if:

       EINVAL The dirp argument does not refer to a valid directory
              stream.

       The following sections are informative.

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Примеры (Examples)

None.

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Использование в приложениях (Application usage)

The dirfd() function is intended to be a mechanism by which an
       application may obtain a file descriptor to use for the fchdir()
       function.

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Обоснование (Rationale)

This interface was introduced because the Base Definitions volume
       of POSIX.1‐2017 does not make public the DIR data structure.
       Applications tend to use the fchdir() function on the file
       descriptor returned by this interface, and this has proven useful
       for security reasons; in particular, it is a better technique
       than others where directory names might change.

       The description uses the term ``a file descriptor'' rather than
       ``the file descriptor''. The implication intended is that an
       implementation that does not use an fd for opendir() could still
       open() the directory to implement the dirfd() function. Such a
       descriptor must be closed later during a call to closedir().

       If it is necessary to allocate an fd to be returned by dirfd(),
       it should be done at the time of a call to opendir().

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Будущие направления (Future directions)

None.

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Смотри также (See also)

closedir(3p), fchdir(3p), fdopendir(3p), fileno(3p), open(3p),
       readdir(3p)

       The Base Definitions volume of POSIX.1‐2017, dirent.h(0p)

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