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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 dif-
       fer (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 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  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
       Interaction of File Descriptors and Standard I/O Streams, fdopen(), fopen(), stdin(), the Base Definitions vol-
       ume 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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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)