Add support for MSVC 2013 Update 5 or newer

Use the CMake WriteCompilerDetectionHeader module to add generate a
header with compatibility macros.

    - For static constants, use `const` instead of `constexpr`

    - Drop `noexcept` if not supported by the compiler

    - Use ASCII string literals if unicode literals are not supported
      and replace unicode opening/closing single quotes with ASCII
      backticks.

CMakeLists.txt

@@ -26,7 +26,7 @@ RETURN()
 
 ENDIF()
 
-cmake_minimum_required(VERSION 2.6)
+cmake_minimum_required(VERSION 3.1)
 project(cxxopts)
 
 set(VERSION "0.0.1")

src/CMakeLists.txt

@@ -18,9 +18,34 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 
-add_executable(example example.cpp)
+add_executable(example example.cpp cxxopts.hpp)
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall")
+# Visual Studio 12 2013 Update 5 or newer is required to fix in-class member
-target_link_libraries(example ${CXXOPTS_LINKER_LIBRARIES})
+# initialization using std::make_shared<type>.
+# https://connect.microsoft.com/VisualStudio/feedbackdetail/view/818825
+if(MSVC AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 18.0.21005.1)
+  message(SEND_ERROR "Visual Studio 12 2013 Update 5 or newer is required.")
+endif()
 
-install(FILES cxxopts.hpp DESTINATION include)
+target_link_libraries(example
+  ${CXXOPTS_LINKER_LIBRARIES}
+  )
+target_compile_features(example PUBLIC
+  cxx_auto_type
+  )
+target_include_directories(example PUBLIC
+  ${CMAKE_CURRENT_BINARY_DIR}
+  )
+
+include(WriteCompilerDetectionHeader)
+write_compiler_detection_header(
+  FILE cxxopts_compiler_detection.h
+  PREFIX cxxopts
+  COMPILERS GNU MSVC Clang
+  FEATURES
+    cxx_unicode_literals
+    cxx_constexpr
+    cxx_noexcept
+)
+
+install(FILES cxxopts.hpp ${CMAKE_CURRENT_BINARY_DIR}/cxxopts_compiler_detection.h DESTINATION include)

src/cxxopts.hpp

@@ -40,6 +40,20 @@ THE SOFTWARE.
 #include <vector>
 #include <string.h>
 
+#include <cxxopts_compiler_detection.h>
+
+#if cxxopts_COMPILER_CXX_CONSTEXPR
+#define cxxopts_CONSTEXPR_OR_CONST constexpr
+#else
+#define cxxopts_CONSTEXPR_OR_CONST const
+#endif
+
+#if cxxopts_COMPILER_CXX_UNICODE_LITERALS
+#define cxxopts_U8(x) u8 ## x
+#else
+#define cxxopts_U8(x) x
+#endif
+
 //when we ask cxxopts to use Unicode, help strings are processed using ICU,
 //which results in the correct lengths being computed for strings when they
 //are formatted for the help output
@@ -272,7 +286,7 @@ namespace cxxopts
     }
 
     virtual const char*
-    what() const noexcept
+    what() const cxxopts_NOEXCEPT
     {
       return m_message.c_str();
     }
@@ -304,7 +318,7 @@ namespace cxxopts
   {
     public:
     option_exists_error(const std::string& option)
-    : OptionSpecException(u8"Option ‘" + option + u8"’ already exists")
+    : OptionSpecException(cxxopts_U8("Option `") + option + cxxopts_U8("` already exists"))
     {
     }
   };
@@ -313,7 +327,7 @@ namespace cxxopts
   {
     public:
     invalid_option_format_error(const std::string& format)
-    : OptionSpecException(u8"Invalid option format ‘" + format + u8"’")
+    : OptionSpecException(cxxopts_U8("Invalid option format `") + format + cxxopts_U8("`"))
     {
     }
   };
@@ -322,7 +336,7 @@ namespace cxxopts
   {
     public:
     option_not_exists_exception(const std::string& option)
-    : OptionParseException(u8"Option ‘" + option + u8"’ does not exist")
+    : OptionParseException(cxxopts_U8("Option `") + option + cxxopts_U8("` does not exist"))
     {
     }
   };
@@ -331,7 +345,7 @@ namespace cxxopts
   {
     public:
     missing_argument_exception(const std::string& option)
-    : OptionParseException(u8"Option ‘" + option + u8"’ is missing an argument")
+    : OptionParseException(cxxopts_U8("Option `") + option + cxxopts_U8("` is missing an argument"))
     {
     }
   };
@@ -340,7 +354,7 @@ namespace cxxopts
   {
     public:
     option_requires_argument_exception(const std::string& option)
-    : OptionParseException(u8"Option ‘" + option + u8"’ requires an argument")
+    : OptionParseException(cxxopts_U8("Option `") + option + cxxopts_U8("` requires an argument"))
     {
     }
   };
@@ -354,8 +368,8 @@ namespace cxxopts
       const std::string& arg
     )
     : OptionParseException(
-        u8"Option ‘" + option + u8"’ does not take an argument, but argument‘"
+        cxxopts_U8("Option `") + option + cxxopts_U8("` does not take an argument, but argument`")
-        + arg + "’ given")
+        + arg + "` given")
     {
     }
   };
@@ -364,7 +378,7 @@ namespace cxxopts
   {
     public:
     option_not_present_exception(const std::string& option)
-    : OptionParseException(u8"Option ‘" + option + u8"’ not present")
+    : OptionParseException(cxxopts_U8("Option `") + option + cxxopts_U8("` not present"))
     {
     }
   };
@@ -377,7 +391,7 @@ namespace cxxopts
       const std::string& arg
     )
     : OptionParseException(
-      u8"Argument ‘" + arg + u8"’ failed to parse"
+      cxxopts_U8("Argument `") + arg + cxxopts_U8("` failed to parse")
     )
     {
     }
@@ -429,25 +443,25 @@ namespace cxxopts
     template <typename T>
     struct value_has_arg
     {
-      static constexpr bool value = true;
+      static cxxopts_CONSTEXPR_OR_CONST bool value = true;
     };
 
     template <>
     struct value_has_arg<bool>
     {
-      static constexpr bool value = false;
+      static cxxopts_CONSTEXPR_OR_CONST bool value = false;
     };
 
     template <typename T>
     struct type_is_container
     {
-      static constexpr bool value = false;
+      static cxxopts_CONSTEXPR_OR_CONST bool value = false;
     };
 
     template <typename T>
     struct type_is_container<std::vector<T>>
     {
-      static constexpr bool value = true;
+      static cxxopts_CONSTEXPR_OR_CONST bool value = true;
     };
 
     template <typename T>
@@ -822,8 +836,8 @@ namespace cxxopts
   namespace
   {
 
-    constexpr int OPTION_LONGEST = 30;
+    cxxopts_CONSTEXPR_OR_CONST int OPTION_LONGEST = 30;
-    constexpr int OPTION_DESC_GAP = 2;
+    cxxopts_CONSTEXPR_OR_CONST int OPTION_DESC_GAP = 2;
 
     std::basic_regex<char> option_matcher
       ("--([[:alnum:]][-_[:alnum:]]+)(=(.*))?|-([a-zA-Z]+)");