msvcrt: Added support for _TRUNCATE flag in wcsncpy_s.

dlls/msvcrt/tests/string.c

@@ -682,6 +682,12 @@ static void test_wcscpy_s(void)
     ret = p_wcsncpy_s(szDestShort, 8, szLongText, sizeof(szLongText)/sizeof(WCHAR));
     ok(ret == ERANGE || ret == EINVAL, "expected ERANGE/EINVAL got %d\n", ret);
     ok(szDestShort[0] == 0, "szDestShort[0] not 0\n");
+
+    szDest[0] = 'A';
+    ret = p_wcsncpy_s(szDest, 5, szLongText, -1);
+    ok(ret == STRUNCATE, "expected STRUNCATE got %d\n", ret);
+    ok(szDest[4] == 0, "szDest[4] not 0\n");
+    ok(!memcmp(szDest, szLongText, 4*sizeof(WCHAR)), "szDest = %s\n", wine_dbgstr_w(szDest));
 }
 
 static void test__wcsupr_s(void)

dlls/msvcrt/wcs.c

@@ -1230,6 +1230,7 @@ INT CDECL MSVCRT_wcsncpy_s( MSVCRT_wchar_t* wcDest, MSVCRT_size_t numElement, co
                             MSVCRT_size_t count )
 {
     MSVCRT_size_t size = 0;
+    INT ret = 0;
 
     if (!wcDest || !numElement)
         return MSVCRT_EINVAL;
@@ -1242,8 +1243,12 @@ INT CDECL MSVCRT_wcsncpy_s( MSVCRT_wchar_t* wcDest, MSVCRT_size_t numElement, co
     }
 
     size = min(strlenW(wcSrc), count);
-
-    if (size >= numElement)
+    if (count==MSVCRT__TRUNCATE && size>=numElement)
+    {
+        ret = MSVCRT_STRUNCATE;
+        size = numElement-1;
+    }
+    else if (size >= numElement)
     {
         return MSVCRT_ERANGE;
     }
@@ -1251,7 +1256,7 @@ INT CDECL MSVCRT_wcsncpy_s( MSVCRT_wchar_t* wcDest, MSVCRT_size_t numElement, co
     memcpy( wcDest, wcSrc, size*sizeof(WCHAR) );
     wcDest[size] = '\0';
 
-    return 0;
+    return ret;
 }
 
 /******************************************************************