[Bug libc/9674] New: mbtowc keeps internal state even for stateless encodings

["bruno at clisp dot org" <sourceware-bugzilla at sourceware dot org>]

Run the following program on a system with a fr_FR.UTF-8 locale.
===================================================================
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <wchar.h>

int main ()
{
  int locale_found = setlocale (LC_ALL, "fr_FR.UTF-8") != NULL;
  printf ("%d\n", locale_found);

  printf ("%d\n", mbtowc (NULL, NULL, 0));

  static const char input[4] = { 195, 188, 195, 159 };
  wchar_t wc;

  int res2a = mbtowc (&wc, input, 4);
  printf ("%d\n", res2a);

  int res1 = mbtowc (&wc, input, 1);
  printf ("%d\n", res1);

  int res2b = mbtowc (&wc, input, 4);
  printf ("%d\n", res2b);

  return 0;
}
===================================================================
$ gcc -O -Wall foo.c
$ ./a.out 
1
0
2
-1
-1

Expected output:

1
0
2
-1
2

Rationale:
The first line shows that the locale was correctly set. So the locale encoding
is UTF-8.
The second line that the UTF-8 encoding is non state dependent.
The third and fifth line show that the same call has different results, that
is, it must depend on a hidden state.
But the mbtowc specification says that "For a state-dependent encoding ...
Subsequent calls with s as other than a null pointer shall cause the internal 
state of the function to be altered as necessary."
However, the encoding in use here is not state dependent. Hence the function's
results should not depend on hidden state.

Reference:
POSIX:2008 specification of mbtowc:
<http://www.opengroup.org/onlinepubs/9699919799/functions/mbtowc.html>

-- 
           Summary: mbtowc keeps internal state even for stateless encodings
           Product: glibc
           Version: 2.8
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper at redhat dot com
        ReportedBy: bruno at clisp dot org
                CC: glibc-bugs at sources dot redhat dot com
 GCC build triplet: i686-suse-linux
  GCC host triplet: i686-suse-linux
GCC target triplet: i686-suse-linux


http://sourceware.org/bugzilla/show_bug.cgi?id=9674

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