diff --git a/src/strings.cpp b/src/strings.cpp
--- a/src/strings.cpp
+++ b/src/strings.cpp
@@ -196,8 +196,11 @@ bool HaveDParamChanged(const std::vector
{
bool changed = false;
for (size_t i = 0; !changed && i < backup.size(); i++) {
- if (backup[i].string.has_value()) {
- changed = backup[i].string.value() != (const char *)(size_t)_global_string_params.GetParam(i);
+ bool global_has_string = _global_string_params.GetParamStr(i) != nullptr;
+ if (global_has_string != backup[i].string.has_value()) return true;
+
+ if (global_has_string) {
+ changed = backup[i].string.value() != _global_string_params.GetParamStr(i);
} else {
changed = backup[i].data != _global_string_params.GetParam(i);
}
diff --git a/src/tests/CMakeLists.txt b/src/tests/CMakeLists.txt
--- a/src/tests/CMakeLists.txt
+++ b/src/tests/CMakeLists.txt
@@ -2,5 +2,6 @@ add_test_files(
landscape_partial_pixel_z.cpp
math_func.cpp
string_func.cpp
+ strings_func.cpp
test_main.cpp
)
diff --git a/src/tests/strings_func.cpp b/src/tests/strings_func.cpp
new file mode 100644
--- /dev/null
+++ b/src/tests/strings_func.cpp
@@ -0,0 +1,52 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see .
+ */
+
+/** @file strings_func.cpp Test functionality from strings_func. */
+
+#include "../stdafx.h"
+
+#include "../3rdparty/catch2/catch.hpp"
+
+#include "../strings_func.h"
+
+TEST_CASE("HaveDParamChanged")
+{
+ SetDParam(0, 0);
+ SetDParamStr(1, "some string");
+
+ std::vector backup;
+ CopyOutDParam(backup, 2);
+
+ CHECK(HaveDParamChanged(backup) == false);
+
+ /* A different parameter 0 (both string and numeric). */
+ SetDParam(0, 1);
+ CHECK(HaveDParamChanged(backup) == true);
+
+ SetDParamStr(0, "some other string");
+ CHECK(HaveDParamChanged(backup) == true);
+
+ /* Back to the original state, nothing should have changed. */
+ SetDParam(0, 0);
+ CHECK(HaveDParamChanged(backup) == false);
+
+ /* A different parameter 1 (both string and numeric). */
+ SetDParamStr(1, "some other string");
+ CHECK(HaveDParamChanged(backup) == true);
+
+ SetDParam(1, 0);
+ CHECK(HaveDParamChanged(backup) == true);
+
+ /* Back to the original state, nothing should have changed. */
+ SetDParamStr(1, "some string");
+ CHECK(HaveDParamChanged(backup) == false);
+
+ /* Changing paramter 2 should not have any effect, as the backup is only 2 long. */
+ SetDParam(2, 3);
+ CHECK(HaveDParamChanged(backup) == false);
+
+}