FILENO(3P) POSIX Programmer's Manual FILENO(3P)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.
NAMEfileno — map a stream pointer to a file descriptor
int fileno(FILE *stream);
The fileno() function shall return the integer file descriptor associ‐
ated with the stream pointed to by stream.
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.
The fileno() function may fail if:
EBADF The stream argument is not a valid stream, or the stream is not
associated with a file.
The following sections are informative.
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).
Section 2.5.1, Interaction of File Descriptors and Standard I/O
Streams, dirfd(), fdopen(), fopen(), stdin
The Base Definitions volume of POSIX.1‐2008, <stdio.h>
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
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IEEE/The Open Group 2013 FILENO(3P)