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 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 Technology -- 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 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 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(3POSIX)