BUG: garbled transliterated fwprintf(stderr, ...) output

[Markus Kuhn <Markus dot Kuhn at cl dot cam dot ac dot uk>]

BUG REPORT

May be the earlier reported problem has not even much to do with just
ungraceful behaviour in the case of non-strictly-ISO-portable concurrent
use of byte and wide functions. It seems that the use of wide functions
alone has already severe problems just because stderr is used (still
with the recent 2.1.93 CVS snapshot):

Test program:

-----------------------------------------------------------------
#define _ISOC99_SOURCE   /* argl */

#include <stdio.h>
#include <wchar.h>

int main() {

  fwprintf(stderr, L"Schöne Grüße!\n");
  fwprintf(stderr, L"Have a nice day!\n");

  return 0;
}
-----------------------------------------------------------------

Output:

-----------------------------------------------------------------
SchoHave a nice day!
-----------------------------------------------------------------

Output of strace:

-----------------------------------------------------------------
...
write(2, "S", 1S)                        = 1
write(2, "c", 1c)                        = 1
write(2, "h", 1h)                        = 1
write(2, "o", 1o)                        = 1
write(2, "H", 1H)                        = 1
write(2, "a", 1a)                        = 1
write(2, "v", 1v)                        = 1
write(2, "e", 1e)                        = 1
write(2, " ", 1 )                        = 1
write(2, "a", 1a)                        = 1
write(2, " ", 1 )                        = 1
write(2, "n", 1n)                        = 1
write(2, "i", 1i)                        = 1
write(2, "c", 1c)                        = 1
write(2, "e", 1e)                        = 1
write(2, " ", 1 )                        = 1
write(2, "d", 1d)                        = 1
write(2, "a", 1a)                        = 1
write(2, "y", 1y)                        = 1
write(2, "!", 1!)                        = 1
write(2, "\n", 1
)                       = 1
_exit(0)                                = ?
-----------------------------------------------------------------

Interestingly, if I use

  wprintf(L"Schöne Grüße!\n");
  wprintf(L"Have a nice day!\n");

instead of

  fwprintf(stderr, L"Schöne Grüße!\n");
  fwprintf(stderr, L"Have a nice day!\n");

then I get on stdout the correct output

-----------------------------------------------------------------
Schoene Gruesse!
Have a nice day!
-----------------------------------------------------------------

and strace reports as expected

-----------------------------------------------------------------
write(1, "Schoene Gruesse!\n", 17Schoene Gruesse!
)      = 17
write(1, "Have a nice day!\n", 17Have a nice day!
)      = 17
-----------------------------------------------------------------

which is obviously what I had also hoped to see for the stderr case.

The effect seems to be triggered by the translitaration of the "ü" to
"ue" on stderr, as nothing goes wrong with

  fwprintf(stderr, L"Schone Gruse!\n");

Markus

-- 
Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
Email: mkuhn at acm.org,  WWW: <http://www.cl.cam.ac.uk/~mgk25/>