fileno(3) — Linux manual page

fileno(3)               Library Functions Manual               fileno(3)

NAME         top

       fileno - obtain file descriptor of a stdio stream

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <stdio.h>

       int fileno(FILE *stream);

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       fileno():
           _POSIX_C_SOURCE

DESCRIPTION         top

       The function fileno() examines the argument stream and returns
       the integer file descriptor used to implement this stream.  The
       file descriptor is still owned by stream and will be closed when
       fclose(3) is called.  Duplicate the file descriptor with dup(2)
       before passing it to code that might close it.

       For the nonlocking counterpart, see unlocked_stdio(3).

RETURN VALUE         top

       On success, fileno() returns the file descriptor associated with
       stream.  On failure, -1 is returned and errno is set to indicate
       the error.

ERRORS         top

       EBADF  stream is not associated with a file.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌─────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                           │ Attribute     │ Value   │
       ├─────────────────────────────────────┼───────────────┼─────────┤
       │ fileno()                            │ Thread safety │ MT-Safe │
       └─────────────────────────────────────┴───────────────┴─────────┘

STANDARDS         top

       POSIX.1-2008.

HISTORY         top

       POSIX.1-2001.

SEE ALSO         top

       open(2), fdopen(3), stdio(3), unlocked_stdio(3)

COLOPHON         top

       This page is part of the man-pages (Linux kernel and C library
       user-space interface documentation) project.  Information about
       the project can be found at 
       ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report
       for this manual page, see
       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
       This page was obtained from the tarball man-pages-6.9.1.tar.gz
       fetched from
       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
       2024-06-26.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-
       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to
       man-pages@man7.org

Linux man-pages 6.9.1          2024-05-02                      fileno(3)

Pages that refer to this page: fsync(2),  fclose(3),  ferror(3),  fflush(3),  fmemopen(3),  fopen(3),  open_memstream(3),  pcap_file(3pcap),  stdio(3)

HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.