FILENO
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
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.
NAME
fileno
--- map a stream pointer to a file descriptor
SYNOPSIS
#include <stdio.h>
int fileno(FILE *stream);
DESCRIPTION
The
fileno()
function shall return the integer file descriptor associated with
the stream pointed to by
stream.
RETURN VALUE
Upon successful completion,
fileno()
shall return the integer value of the file descriptor associated with
stream.
Otherwise, the value -1 shall be returned and
errno
set to indicate the error.
ERRORS
The
fileno()
function shall fail if:
- EBADF
-
The stream is not associated with a file.
The
fileno()
function may fail if:
- EBADF
-
The file descriptor underlying
stream
is not a valid file descriptor.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
Without some specification of which file descriptors are associated
with these streams, it is impossible for an application to set up the
streams for another application it starts with
fork()
and
exec.
In particular, it would not be possible to write a portable version of
the
sh
command interpreter (although there may be other constraints that would
prevent that portability).
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.5.1,
Interaction of File Descriptors and Standard I/O Streams,
dirfd(),
fdopen(),
fopen(),
stdin
The Base Definitions volume of POSIX.1-2017,
<stdio.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .