[Bug c/37771] New: warning: implicit declaration of function 'fileno'

[Bug c/37771] New: warning: implicit declaration of function 'fileno'

[mathieu dot malaterre at gmail dot com]

The following piece of code should compile without warning:

#include <stdio.h>

int main()
{
  (void)fileno(0);
  return 0;
}


Using:

$ gcc  -Wall -W -pedantic -ansi -Werror f.c                                     
cc1: warnings being treated as errors
f.c: In function 'main':
f.c:5: warning: implicit declaration of function 'fileno'


With:
$ gcc --version                                                                 
gcc (GCC) 4.2.3 (Debian 4.2.3-3)
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


thanks


-- 
           Summary:  warning: implicit declaration of function 'fileno'
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mathieu dot malaterre at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37771

[Bug c/37771] warning: implicit declaration of function 'fileno'

[paolo dot carlini at oracle dot com]

------- Comment #1 from paolo dot carlini at oracle dot com  2008-10-08 12:48 -------
The warning is correct: by default, fileno, not being a standard C function, is
simply not declared in the <stdio.h> header of your linux machine. A quick look
to the man page reveals that the function is declared when, e.g., _POSIX_SOURCE
is defined.


-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID
            Summary| warning: implicit          |warning: implicit
                   |declaration of function     |declaration of function
                   |'fileno'                    |'fileno'


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37771

[Bug c/37771] warning: implicit declaration of function 'fileno'

[mathieu dot malaterre at gmail dot com]

------- Comment #2 from mathieu dot malaterre at gmail dot com  2008-10-08 12:52 -------
Hum... ok nevermind. My man page must be outdated.

ref:

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

NAME
       clearerr, feof, ferror, fileno - check and reset stream status

SYNOPSIS
       #include <stdio.h>

       void clearerr(FILE *stream);
       int feof(FILE *stream);
       int ferror(FILE *stream);
       int fileno(FILE *stream);

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 non-zero if it is set.  The end-of-file
       indicator can only be cleared by the function clearerr().

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

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

       For non-locking 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.)

CONFORMING TO
       The functions clearerr(), feof(), and ferror() conform to C89.

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

                                  2001-10-16                         FERROR(3)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37771

[Bug c/37771] warning: implicit declaration of function 'fileno'

[paolo dot carlini at oracle dot com]

------- Comment #3 from paolo dot carlini at oracle dot com  2008-10-08 12:56 -------
Note, anyway, that fileno is not present in CONFORMING TO as a C89 function.
Which indeed it is not. In any case, the ultimate reference is the C Standard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37771