fflush does not detect error case when operating on stdin

[Bernard WEISSER]

Hello,

I found a code that tried to fflush on stdin and that returned a 0
status but a non-nul errno value.

My configuration is :

Linux mars 2.4.26 #6 Mon Jun 14 19:07:27 PDT 2004 i686
>Release:       libc-2.3.2
>Environment:
        <machine, os, target, libraries (multiple lines)>
Host type: i486-slackware-linux-gnu
System: Linux mars 2.4.26 #6 Mon Jun 14 19:07:27 PDT 2004 i686 unknown 
unknown GNU/Linux
Architecture: i686

Addons: linuxthreads
Build CFLAGS: -g -O2 -march=i486 -mcpu=i686
Build CC: i486-slackware-linux-gcc
Compiler version: 3.3.3
Kernel headers: 2.4.26
Symbol versioning: yes
Build static: yes
Build shared: yes
Build pic-default: no
Build profile: yes
Build omitfp: no
Build bounded: no
Build static-nss: no

Here is the code :

/*
* Execution gives the following output :
*
* Enter an integer, then a CR : 123
* errno = 0
* flushing stdin...
* fflush OK                     <============= should not be OK
* errno = Illegal seek
*
* When flusing the non-empty stdin, fflush does not return -1, but 0.
* -1 was expected, since fflush should be applied only to an output stream.
*  An error situation should have occured, since errno is also set to
*  indicate an "Illegal seek" error.
*/

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int   main (void)
{
  int   i, status ;

  printf ("Enter an integer, then a CR : ") ;
  if (scanf ("%d", &i) != 1) {
     printf ("scanf error\n") ;
     exit (1) ;
  }
  printf ("errno = %d\n", errno) ;

  printf ("flushing stdin...\n") ;

  status = fflush (stdin) ;

  if (status != 0) {
     printf ("fflush error\n") ;
  }
  else {
     printf ("fflush OK\n") ;
  }

  if (errno == -1) {
     perror ("fflush") ;
  }
  else {
     printf ("errno = %s\n", strerror (errno)) ;
  }

  return 0 ;
}

Do you think this is a bug ?