2 files changed, 94 insertions, 1 deletions

diff --git a/src/regress/lib/libc/stdio/Makefile b/src/regress/lib/libc/stdio/Makefile
index 3f2c2bab8e..fa5ebabee1 100644
--- a/src/regress/lib/libc/stdio/Makefile
+++ b/src/regress/lib/libc/stdio/Makefile
@@ -1,8 +1,11 @@
-# $OpenBSD: Makefile,v 1.2 2025/05/25 00:20:54 yasuoka Exp $
+# $OpenBSD: Makefile,v 1.3 2025/05/25 05:32:45 yasuoka Exp $
 
 PROGS=          test_fflush
 CLEANFILES=     test_fflush.tmp
 
+PROGS+=         test_ungetwc
+CLEANFILES+=    test_ungetwc.tmp
+
 PROGS+=         test___freading
 CLEANFILES+=    test___freading.tmp
 
diff --git a/src/regress/lib/libc/stdio/test_ungetwc.c b/src/regress/lib/libc/stdio/test_ungetwc.c
new file mode 100644
index 0000000000..bb4e853020
--- /dev/null
+++ b/src/regress/lib/libc/stdio/test_ungetwc.c
@@ -0,0 +1,90 @@
+/*      $OpenBSD: test_ungetwc.c,v 1.1 2025/05/25 05:32:45 yasuoka Exp $        */
+
+/*
+ * Copyright (c) 2025 YASUOKA Masahiko <yasuoka@yasuoka.net>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <locale.h>
+#include <wchar.h>
+
+/* we use assert() */
+#undef  NDEBUG
+
+#define TMPFILENAME     "test_ungetwc.tmp"
+
+void setupw(void);
+void test_fflush_ungetwc0(void);
+
+void
+setupw(void)
+{
+        FILE    *fp;
+
+        /* common setup */
+        unlink(TMPFILENAME);
+        fp = fopen(TMPFILENAME, "w+");
+        assert(fp != NULL);
+        /* Konnitiwa Sekai(in Kanji) */
+        fputws(L"\u3053\u3093\u306b\u3061\u308f \u4e16\u754c\n", fp);
+        fclose(fp);
+}
+
+/* fflush work with reading file and seekable + ungetwc */
+void
+test_fflush_ungetwc0(void)
+{
+        int      r;
+        wchar_t  buf[80];
+        FILE    *fp;
+
+        setupw();
+
+        fp = fopen(TMPFILENAME, "r");
+
+        assert(fp != NULL);
+        assert(fgetwc(fp) == L'\u3053');        /* Ko */
+        assert(fgetwc(fp) == L'\u3093');        /* N  */
+        assert(fgetwc(fp) == L'\u306b');        /* Ni */
+        assert(fgetwc(fp) == L'\u3061');        /* Ti */
+        assert(fgetwc(fp) == L'\u308f');        /* Wa */
+
+        /* push 263A(smile) back */
+        assert(ungetwc(L'\u263a', fp));
+
+        /* we support 1 push back wchar_t */
+        assert(fgetwc(fp) == L'\u263a');
+
+        /* can read reset of that */
+        fgetws(buf, sizeof(buf), fp);
+        assert(wcscmp(buf, L" \u4e16\u754c\n") == 0);
+
+        r = fclose(fp);
+        assert(r == 0);
+}
+
+int
+main(int argc, char *argv[])
+{
+        setlocale(LC_ALL, "C.UTF-8");
+
+        test_fflush_ungetwc0();
+
+        exit(0);
+}