fileno

       #include <stdio.h>

       void clearerr(FILE *stream);

       int feof(FILE *stream);

       int ferror(FILE *stream);

       int fileno(FILE *stream);

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

       fileno(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE

DESCRIPTION
       The function clearerr() clears the end-of-file and error indicators for
       the stream pointed to by stream.

       The function feof() tests the  end-of-file  indicator  for  the  stream
       pointed  to by stream, returning nonzero if it is set.  The end-of-file
       indicator can be cleared only by the function clearerr().

       The function ferror() tests the error indicator for the stream  pointed
       to  by stream, returning nonzero if it is set.  The error indicator can
       be reset only by the clearerr() function.

       The function fileno() examines the  argument  stream  and  returns  its
       integer descriptor.

       For nonlocking counterparts, see unlocked_stdio(3).

ERRORS
       These  functions  should  not fail and do not set the external variable
       errno.  (However, in case fileno() detects that its argument is  not  a
       valid stream, it must return -1 and set errno to EBADF.)

ATTRIBUTES
       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       +--------------------+---------------+---------+
       |Interface           | Attribute     | Value   |
       +--------------------+---------------+---------+
       |clearerr(), feof(), | Thread safety | MT-Safe |
       |ferror(), fileno()  |               |         |
       +--------------------+---------------+---------+
CONFORMING TO
       The functions clearerr(), feof(), and ferror()  conform  to  C89,  C99,
       POSIX.1-2001, and POSIX.1-2008.

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

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