fileno(3) — Linux manual page

fileno(3)               Library Functions Manual               fileno(3)

NAME

       fileno - obtain file descriptor of a stdio stream

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdio.h>

       int fileno(FILE *stream);

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

       fileno():
           _POSIX_C_SOURCE

DESCRIPTION

       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

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

ERRORS

       EBADF  stream is not associated with a file.

ATTRIBUTES

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

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001.

SEE ALSO

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

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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)

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