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)