wchar: bug #1471: fix cornercase in mbrtowc

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libc/misc/wchar/wchar.c

@@ -286,6 +286,8 @@ size_t mbrtowc(wchar_t *__restrict pwc, const char *__restrict s,
 		s = empty_string;
 		n = 1;
 	} else if (*s == '\0') {
+		if (pwc)
+			*pwc = '\0';
 	/* According to the ISO C 89 standard this is the expected behaviour.  */
 		return 0;
 	} else if (!n) {

test/.gitignore

@@ -96,6 +96,7 @@ locale-mbwc/tst_wctomb
 locale-mbwc/tst_wctrans
 locale-mbwc/tst_wctype
 locale-mbwc/tst_wcwidth
+locale-mbwc/tst2_mbrtowc
 locale/show-ucs-data
 locale/tst-digits
 locale/tst-langinfo

test/locale-mbwc/Makefile.in

@@ -15,8 +15,8 @@ TESTS := tst_iswalnum tst_iswalpha tst_iswcntrl          \
 	 tst_wcspbrk tst_wcsrtombs tst_wcsspn tst_wcsstr \
 	 tst_wcstod tst_wcstok tst_wcstombs tst_wcswidth \
 	 tst_wcsxfrm tst_wctob tst_wctomb tst_wctrans    \
-	 tst_wctype tst_wcwidth tst_strfmon
-
+	 tst_wctype tst_wcwidth tst_strfmon \
+	 tst2_mbrtowc
 
 # NOTE: For now disabled tst_strfmon to avoid build failure.
 TESTS_DISABLED := tst_strfmon

test/locale-mbwc/tst2_mbrtowc.c

@@ -0,0 +1,21 @@
+#include <wchar.h>
+#include <assert.h>
+#include <stdlib.h>
+
+/* bugs.uclibc.org/1471 : make sure output is 0  */
+static int
+do_test(void)
+{
+  wchar_t output;
+  int result;
+
+  output = L'A';		/* anything other than 0 will do... */
+  result = mbrtowc (&output, "", 1, 0);
+
+  assert (result == 0);
+  assert (output == 0);
+
+  return EXIT_SUCCESS;
+}
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"