chore: enable to use __cplusplus on MSVC

related: https://github.com/ToruNiina/toml11/issues/112

.github/workflows/main.yml

@@ -99,6 +99,7 @@ jobs:
       - name: Configure
         shell: cmd
         run: |
+            file --mime-encoding tests/test_literals.cpp
             mkdir build
             cd build
             cmake ../ -G "NMake Makefiles" -DCMAKE_CXX_STANDARD=${{ matrix.standard }} -DBoost_ADDITIONAL_VERSIONS=1.72.0 -DBoost_USE_MULTITHREADED=ON -DBoost_ARCHITECTURE=-x64 -DBoost_NO_BOOST_CMAKE=ON -DBOOST_ROOT=%BOOST_ROOT_1_72_0%
@@ -109,6 +110,7 @@ jobs:
       - name: Test
         working-directory: ./build
         run: |
+            ./tests/test_literals --log_level=all
             file --mime-encoding tests/toml/tests/example.toml
             file --mime-encoding tests/toml/tests/fruit.toml
             file --mime-encoding tests/toml/tests/hard_example.toml

CMakeLists.txt

@@ -37,6 +37,10 @@ else()
     endif()
 endif()
 
+if(MSVC)
+    add_definitions("/Zc:__cplusplus")
+endif()
+
 # Set some common directories
 include(GNUInstallDirs)
 set(toml11_install_cmake_dir         ${CMAKE_INSTALL_LIBDIR}/cmake/toml11)

tests/test_literals.cpp

@@ -264,6 +264,20 @@ BOOST_AUTO_TEST_CASE(test_value_as_u8_literal)
         const toml::value v4 = u8R"('''foo''')"_toml;
         const toml::value v5 = u8R"("ひらがな")"_toml;
 
+        // XXX
+#ifndef __cpp_char8_t
+        {
+            const char* l = u8R"(ひらがな)";
+            BOOST_TEST_MESSAGE(l);
+            while(*l != '\0')
+            {
+                const int tmp(*l);
+                BOOST_TEST_MESSAGE(std::hex << tmp);
+                ++l;
+            }
+        }
+#endif
+
         BOOST_TEST(v1.is_string());
         BOOST_TEST(v2.is_string());
         BOOST_TEST(v3.is_string());