refs #52: Test and fix MSVC linker error on duplicated symbols

Author: beutlich

ExternData/Resources/BuildProjects/CMake/test.cmake

@@ -46,6 +46,8 @@ if(EXISTS "${ED_TEST_DIR}")
   foreach(TEST ${ED_TESTS})
     add_executable(${TEST}
       "${ED_TEST_DIR}/${TEST}.cc"
+      "${ED_TEST_DIR}/Test_Linkage.cc"
+      "${ED_TEST_DIR}/Test_Linkage.c"
       "${ED_TEST_DIR}/Constants.h"
     )
     target_compile_features(${TEST} PRIVATE cxx_std_17)
@@ -73,6 +75,8 @@ if(EXISTS "${ED_TEST_DIR}")
     )
     if(UNIX)
       list(APPEND ED_ALL_LIBS m)
+    elseif(MSVC)
+      target_link_options(${TEST} PRIVATE "/FORCE:MULTIPLE")
     endif()
     target_link_libraries(${TEST} PRIVATE ${ED_ALL_LIBS})
 

ExternData/Resources/Include/msvc_compatibility.h

@@ -23,14 +23,14 @@
 extern "C" {
 #endif
 
-extern long timezone = 0;
+__declspec(selectany) extern long timezone = 0;
 
 #if defined(G_HAS_CONSTRUCTORS)
 #ifdef G_DEFINE_CONSTRUCTOR_NEEDS_PRAGMA
 #pragma G_DEFINE_CONSTRUCTOR_PRAGMA_ARGS(Timezone_initialize)
 #endif
 G_DEFINE_CONSTRUCTOR(Timezone_initialize)
-static void Timezone_initialize(void) {
+static inline void Timezone_initialize(void) {
 	_get_timezone(&timezone);
 }
 #endif

ExternData/Resources/Test/Test_Linkage.c

@@ -0,0 +1,9 @@
+/* Test_Linkage.c
+ *
+ * Copyright (C) 2015-2025, Thomas Beutlich
+ * All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "../Include/msvc_compatibility.h"

ExternData/Resources/Test/Test_Linkage.cc

@@ -0,0 +1,10 @@
+/* Test_Linkage.cc
+ *
+ * Copyright (C) 2015-2025, Thomas Beutlich
+ * All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "../Include/msvc_compatibility.h"
+#include "Constants.h"