fileno(3p) — Linux manual page

FILENO(3P)              POSIX Programmer's Manual             FILENO(3P)

PROLOG         top

       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         top

       fileno — map a stream pointer to a file descriptor

SYNOPSIS         top

       #include <stdio.h>

       int fileno(FILE *stream);

DESCRIPTION         top

       The fileno() function shall return the integer file descriptor
       associated with the stream pointed to by stream.

RETURN VALUE         top

       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         top

       The fileno() function shall fail if:

       EBADF  The stream is not associated with a file.

       The fileno() function may fail if:

       EBADF  The file descriptor underlying stream is not a valid file
              descriptor.

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       None.

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       Section 2.5.1, Interaction of File Descriptors and Standard I/O
       Streams, dirfd(3p), fdopen(3p), fopen(3p), stdin(3p)

       The Base Definitions volume of POSIX.1‐2017, stdio.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017                        FILENO(3P)

Pages that refer to this page: stdio.h(0p),  dirfd(3p),  stdin(3p)

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