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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.
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  associ-
       ated 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.

       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 par-
       ticular, 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
       Interaction of File Descriptors and  Standard  I/O  Streams,  fdopen(),
       fopen(),  stdin(), the Base Definitions volume of IEEE Std 1003.1-2001,
       <stdio.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 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 .

IEEE/The Open Group                  2003                           FILENO(3P)