Update.

* libio/Makefile (tests): Add bug-ungetwc2.
	* libio/bug-ungetwc2.c: New file.

libio/bug-ungetwc2.c

@@ -0,0 +1,89 @@
+#define _XOPEN_SOURCE 500
+#include <errno.h>
+#include <error.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <locale.h>
+#include <wchar.h>
+
+const char test_locale[] = "en_US.UTF-8";
+const wchar_t write_wchars[] = {L'A', 0x00C4, L'B', L'\0'};
+                                /* `0x00C4' is A with diaeresis. */
+size_t last_pos = 2;            /* Which character is last one to read. */
+wint_t unget_wchar = L'C';      /* Ungotten ide characters. */
+
+char *fname;
+
+
+static int do_test (void);
+#define TEST_FUNCTION do_test ()
+
+#include "../test-skeleton.c"
+
+
+static int
+do_test (void)
+{
+  size_t i;
+  wint_t wc;
+  FILE *fp;
+  int fd;
+
+  fname = (char *) malloc (strlen (test_dir) + sizeof "/bug-ungetwc2.XXXXXX");
+  if (fname == NULL)
+    {
+      puts ("no memory");
+      return 1;
+    }
+  strcpy (stpcpy (fname, test_dir), "/bug-ungetwc2.XXXXXX");
+  fd = mkstemp (fname);
+  if (fd == -1)
+    {
+      printf ("cannot open temporary file: %m\n");
+      return 1;
+    }
+  add_temp_file (fname);
+
+  printf ("\nNote: This program runs on %s locale.\n\n", test_locale);
+
+  if (setlocale (LC_ALL, test_locale) == NULL)
+    {
+      fprintf (stderr, "Cannot use `%s' locale.\n", test_locale);
+      exit (EXIT_FAILURE);
+    }
+
+  /* Output to the file. */
+  if ((fp = fdopen (fd, "w")) == NULL)
+    {
+      fprintf (stderr, "Cannot make `%s' file.\n", fname);
+      exit (EXIT_FAILURE);
+    }
+  fprintf (fp, "%ls", write_wchars);
+  fclose (fp);
+
+  /* Read from the file. */
+  fp = fopen (fname, "r");
+  if (fp == NULL)
+    error (EXIT_FAILURE, errno, "cannot open %s", fname);
+
+  printf ("%s is opened.\n", fname);
+
+  for (i = 0; i < last_pos; i++)
+    {
+      wc = getwc (fp);
+      printf ("> `%lc' is gotten.\n", wc);
+    }
+
+  /* Unget a wide character. */
+  ungetwc (unget_wchar, fp);
+  printf ("< `%lc' is ungotten.\n", unget_wchar);
+
+  /* Reget the wide character. */
+  wc = getwc (fp);
+  printf ("> `%lc' is regotten.\n", wc);
+
+  fflush (stdout);
+  fclose (fp);
+
+  return 0;
+}