posix man page for fileno

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 correspond-
       ing 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 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.

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.1-2008, <stdio.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical 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 Stan-
       dard 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 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 .

IEEE
/The Open Group						       2013								FILENO(3P)