fileno

FILENO(3)                   Linux Programmer's Manual                  FILENO(3)



NAME
       fileno - obtain file descriptor of a stdio stream

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 │
       └──────────────────────────────────────────────┴───────────────┴─────────┘

CONFORMING TO
       The function fileno() conforms to POSIX.1-2001 and POSIX.1-2008.

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

COLOPHON
       This page is part of release 5.13 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



                                   2021-03-22                          FILENO(3)