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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 in-
       teger file descriptor used to implement this stream.  The file descrip-
       tor  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 at-
       tributes(7).

       ┌────────────────────────────────────────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├────────────────────────────────────────────┼───────────────┼─────────┤
       │fileno()                                    │ Thread safety │ MT-Safe │
       └────────────────────────────────────────────┴───────────────┴─────────┘

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

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

Linux man-pages 6.03              2022-12-15                         fileno(3)

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