diff --git a/include/nana/c++defines.hpp b/include/nana/c++defines.hpp
new file mode 100644
index 00000000..6f6417ef
--- /dev/null
+++ b/include/nana/c++defines.hpp
@@ -0,0 +1,178 @@
+/**
+ *	Predefined Symbols for C++
+ *	Nana C++ Library(http://www.nanapro.org)
+ *	Copyright(C) 2016 Jinhao(cnjinhao@hotmail.com)
+ *
+ *	Distributed under the Boost Software License, Version 1.0.
+ *	(See accompanying file LICENSE_1_0.txt or copy at
+ *	http://www.boost.org/LICENSE_1_0.txt)
+ *
+ *	@file  nana/config.hpp
+ *
+ *	@brief Provide switches to adapt to the target OS, use of external libraries or workarounds compiler errors or lack of std C++ support.
+ *
+ *	To control target OS/compiler:
+ *	- NANA_WINDOWS
+ *	- NANA_MINGW
+ *	- NANA_POSIX
+ *	- NANA_LINUX
+ *	- NANA_MACOS
+ *	- NANA_X11
+ *
+ *	External libraries:
+ *	- NANA_LIBPNG, USE_LIBPNG_FROM_OS
+ *	- NANA_LIBJPEG, USE_LIBJPEG_FROM_OS
+ *
+ * (see: Feature-testing recommendations for C++
+ *       in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0096r0.html
+ *       for example: __cpp_lib_experimental_filesystem  = 201406 in <experimental/filesystem)
+ *
+ *	Workaround to known compiler errors, unnecessary warnings or lack of C++11/14/17 support:
+ *	- _SCL_SECURE_NO_WARNNGS, _CRT_SECURE_NO_DEPRECATE (VC)
+ *	- STD_CODECVT_NOT_SUPPORTED (VC RC, <codecvt> is a known issue on libstdc++, it works on libc++)
+ *	- STD_THREAD_NOT_SUPPORTED (GCC < 4.8.1)
+ *	- STD_NUMERIC_CONVERSIONS_NOT_SUPPORTED  (MinGW with GCC < 4.8.1)
+ *	- USE_github_com_meganz_mingw_std_threads  (MinGW with GCC < 4.8.1)
+ *	- STD_NUMERIC_CONVERSIONS_NOT_SUPPORTED (MinGW with GCC < 4.8.1)
+ *	- STD_TO_STRING_NOT_SUPPORTED (MinGW with GCC < 4.8)
+ *	- VERBOSE_PREPROCESSOR, STOP_VERBOSE_PREPROCESSOR
+ *	- STD_make_unique_NOT_SUPPORTED  (MinGW with GCC < 4.8.1)
+ *	  or __cpp_lib_make_unique
+ *	http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0096r0.html#detail.cpp14.n3656
+ */
+
+#ifndef NANA_CXX_DEFINES_INCLUDED
+#define NANA_CXX_DEFINES_INCLUDED
+
+// Select platform  ......
+#if defined(_WIN32) || defined(__WIN32__) || defined(WIN32)	//Microsoft Windows
+	#define NANA_WINDOWS
+
+	// MINGW ...
+	#if defined(__MINGW32__) || defined(__MINGW64__) || defined(MINGW)
+		#define NANA_MINGW
+	#endif // MINGW
+
+#elif defined(APPLE)	//Mac OS X
+	//Symbols for MACOS
+
+	#define NANA_MACOS
+	#define NANA_X11
+
+#elif (defined(linux) || defined(__linux) || defined(__linux__) || defined(__GNU__) || defined(__GLIBC__)) && !defined(_CRAYC)	//Linux
+	#define NANA_LINUX
+	#define NANA_X11
+#else
+#	static_assert(false, "Only Windows and Unix are supported now (Mac OS is experimental)");
+#endif
+
+//Define a symbol for POSIX operating system.
+#if defined(NANA_LINUX) || defined(NANA_MACOS)
+	#define NANA_POSIX
+#endif
+
+
+
+// Select compiler ...
+#if defined(_MSC_VER)	//Microsoft Visual C++
+	#define _SCL_SECURE_NO_WARNNGS
+	#define _CRT_SECURE_NO_DEPRECATE
+	#pragma warning(disable : 4996)
+
+	#if (_MSC_VER == 1900)
+		// google: break any code that tries to use codecvt<char16_t> or codecvt<char32_t>.
+		// google: It appears the C++ libs haven't been compiled with native char16_t/char32_t support.
+		// google: Those definitions are for codecvt<wchar_t>::id, codecvt<unsigned short>::id and codecvt<char>::id respectively.
+		// However, the codecvt<char16_t>::id and codecvt<char32_t>::id definitions aren't there, and indeed, if you look at locale0.cpp in the CRT source code you'll see they're not defined at all.
+		// google: That's a known issue, tracked by an active bug (DevDiv#1060849). We were able to update the STL's headers in response to char16_t/char32_t, but we still need to update the separately compiled sources.
+		#define STD_CODECVT_NOT_SUPPORTED
+	#endif // _MSC_VER == 1900
+
+#elif defined(__clang__)	//Clang
+
+	#include <iosfwd>	//Introduces some implement-specific flags of ISO C++ Library
+	#if defined(__GLIBCPP__) || defined(__GLIBCXX__)
+		//<codecvt> is a known issue on libstdc++, it works on libc++
+		#define STD_CODECVT_NOT_SUPPORTED
+
+
+		#ifndef STD_MAKE_UNIQUE_NOT_SUPPORTED
+			#define STD_MAKE_UNIQUE_NOT_SUPPORTED
+		#endif
+
+	#endif
+
+#elif defined(__GNUC__) //GCC
+
+	#include <iosfwd>	//Introduces some implement-specific flags of ISO C++ Library
+	#if defined(__GLIBCPP__) || defined(__GLIBCXX__)
+		//<codecvt> is a known issue on libstdc++, it works on libc++
+		#define STD_CODECVT_NOT_SUPPORTED
+
+		//It's a known issue of libstdc++ on MinGW
+		//introduce to_string/to_wstring workarounds for disabled capacity of stdlib
+		#ifdef _GLIBCXX_HAVE_BROKEN_VSWPRINTF
+			#if (__GNUC__ < 5)
+			#	define STD_TO_STRING_NOT_SUPPORTED
+			#endif
+
+			#define STD_TO_WSTRING_NOT_SUPPORTED
+		#endif
+	#endif
+
+	#if (__GNUC__ == 4)
+		#if ((__GNUC_MINOR__ < 8) || (__GNUC_MINOR__ == 8 && __GNUC_PATCHLEVEL__ < 1))
+			#define STD_THREAD_NOT_SUPPORTED
+
+			//boost.thread is preferred
+			//but if USE_github_com_meganz_mingw_std_threads is enabled,
+			//boost.thread will be replaced with meganz's mingw-std-threads.
+			// https://github.com/meganz/mingw-std-threads
+			#if !defined( USE_github_com_meganz_mingw_std_threads )
+				//#define USE_github_com_meganz_mingw_std_threads
+			#endif
+		#endif
+
+		#if (__GNUC_MINOR__ < 9)
+			#define STD_MAKE_UNIQUE_NOT_SUPPORTED
+		#endif
+
+		#if defined(NANA_MINGW)
+			//It's a knonwn issue under MinGW
+			#define STD_NUMERIC_CONVERSIONS_NOT_SUPPORTED
+		#endif
+
+		#if (__GNUC_MINOR__ < 8)
+			//introduce to_string/to_wstring workaround for lack of stdlib definitions
+			#ifndef STD_TO_STRING_NOT_SUPPORTED
+			#	define STD_TO_STRING_NOT_SUPPORTED
+			#endif
+
+			#ifndef STD_TO_WSTRING_NOT_SUPPORTED
+			#	define STD_TO_WSTRING_NOT_SUPPORTED
+			#endif
+		#endif
+	#endif
+#endif
+
+
+#if defined(NANA_WINDOWS)
+	#ifndef _UNICODE
+		#define _UNICODE
+	#endif
+
+	#ifndef UNICODE
+		#define UNICODE
+	#endif
+#endif
+
+#if !defined(VERBOSE_PREPROCESSOR)
+    //#define VERBOSE_PREPROCESSOR
+#endif
+
+#if !defined(STOP_VERBOSE_PREPROCESSOR)
+	#define STOP_VERBOSE_PREPROCESSOR
+#endif
+
+
+#endif  // NANA_CXX_DEFINES_INCLUDED
diff --git a/include/nana/config.hpp b/include/nana/config.hpp
index 3136f531..28adebf4 100644
--- a/include/nana/config.hpp
+++ b/include/nana/config.hpp
@@ -9,168 +9,17 @@
  *
  *	@file  nana/config.hpp
  *
- *	@brief Provide switches to adapt to the target OS, use of external libraries or workarounds compiler errors or lack of std C++ support.
- *
- *	To control target OS/compiler:
- *	- NANA_WINDOWS
- *	- NANA_MINGW
- *	- NANA_POSIX
- *	- NANA_LINUX
- *	- NANA_MACOS
- *	- NANA_X11
- *	- NANA_UNICODE
+ *	@brief Provide switches to enable 3rd-party libraries for a certain feature.
  *
  *	External libraries:
  *	- NANA_LIBPNG, USE_LIBPNG_FROM_OS
  *	- NANA_LIBJPEG, USE_LIBJPEG_FROM_OS
- *
- * (see: Feature-testing recommendations for C++
- *       in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0096r0.html
- *       for example: __cpp_lib_experimental_filesystem  = 201406 in <experimental/filesystem)
- *
- *	Workaround to known compiler errors, unnecessary warnings or lack of C++11/14/17 support:
- *	- _SCL_SECURE_NO_WARNNGS, _CRT_SECURE_NO_DEPRECATE (VC)
- *	- STD_CODECVT_NOT_SUPPORTED (VC RC, <codecvt> is a known issue on libstdc++, it works on libc++)
- *	- STD_THREAD_NOT_SUPPORTED (GCC < 4.8.1)
- *	- STD_NUMERIC_CONVERSIONS_NOT_SUPPORTED  (MinGW with GCC < 4.8.1)
- *	- USE_github_com_meganz_mingw_std_threads  (MinGW with GCC < 4.8.1)
- *	- STD_NUMERIC_CONVERSIONS_NOT_SUPPORTED (MinGW with GCC < 4.8.1)
- *	- STD_TO_STRING_NOT_SUPPORTED (MinGW with GCC < 4.8)
- *	- VERBOSE_PREPROCESSOR, STOP_VERBOSE_PREPROCESSOR
- *	- STD_make_unique_NOT_SUPPORTED  (MinGW with GCC < 4.8.1)
- *	  or __cpp_lib_make_unique
- *	http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0096r0.html#detail.cpp14.n3656
  */
 
 #ifndef NANA_CONFIG_HPP
 #define NANA_CONFIG_HPP
 
-// Select platform  ......
-
-	 // Windows:
-	#if defined(_WIN32) || defined(__WIN32__) || defined(WIN32)
-
-		#define NANA_WINDOWS
-
-		// MINGW ...
-		#if defined(__MINGW32__) || defined(__MINGW64__) || defined(MINGW)
-			#define NANA_MINGW
-		#endif // MINGW
-
-	// end Windows
-
-
-	 // MacOS:     who define APPLE ??
-      //#define APPLE
-    #elif defined(APPLE)
-		#define NANA_MACOS
-		#define NANA_X11
-		// how to add this:  include_directories(/opt/X11/include/)
-	// end MacOS
-
-	 // Linux:    (not sure about __GNU__ ??)
-	#elif (defined(linux) || defined(__linux) || defined(__linux__) || defined(__GNU__) || defined(__GLIBC__)) && !defined(_CRAYC)
-		#define NANA_LINUX
-		#define NANA_X11
-	// end Linux
-	#else
-	#	static_assert(false, "Only Windows and Unix are supported now (Mac OS is experimental)");
-	#endif // Select platform
-
-	#if defined(NANA_LINUX) || defined(NANA_MACOS)
-		#define NANA_POSIX
-		#undef NANA_WINDOWS
-	#endif
-// End Select platform  ......
-
-// compilers ...
-
-// MSVC++ versions
-#if defined(_MSC_VER)
-	#define _SCL_SECURE_NO_WARNNGS
-	#define _CRT_SECURE_NO_DEPRECATE
-	#pragma warning(disable : 4996)
-
-	#if (_MSC_VER == 1900)
-		// google: break any code that tries to use codecvt<char16_t> or codecvt<char32_t>.
-		// google: It appears the C++ libs haven't been compiled with native char16_t/char32_t support.
-		// google: Those definitions are for codecvt<wchar_t>::id, codecvt<unsigned short>::id and codecvt<char>::id respectively.
-		// However, the codecvt<char16_t>::id and codecvt<char32_t>::id definitions aren't there, and indeed, if you look at locale0.cpp in the CRT source code you'll see they're not defined at all.
-		// google: That's a known issue, tracked by an active bug (DevDiv#1060849). We were able to update the STL's headers in response to char16_t/char32_t, but we still need to update the separately compiled sources.
-		#define STD_CODECVT_NOT_SUPPORTED
-	#endif // _MSC_VER == 1900
-
-#elif defined(__clang__)	//Clang
-
-	#include <iosfwd>	//Introduces some implement-specific flags of ISO C++ Library
-	#if defined(__GLIBCPP__) || defined(__GLIBCXX__)
-		//<codecvt> is a known issue on libstdc++, it works on libc++
-		#define STD_CODECVT_NOT_SUPPORTED
-
-
-		#ifndef STD_MAKE_UNIQUE_NOT_SUPPORTED
-			#define STD_MAKE_UNIQUE_NOT_SUPPORTED
-		#endif
-
-	#endif
-
-#elif defined(__GNUC__) //GCC
-
-	#include <iosfwd>	//Introduces some implement-specific flags of ISO C++ Library
-	#if defined(__GLIBCPP__) || defined(__GLIBCXX__)
-		//<codecvt> is a known issue on libstdc++, it works on libc++
-		#define STD_CODECVT_NOT_SUPPORTED
-
-		//It's a known issue of libstdc++ on MinGW
-		//introduce to_string/to_wstring workarounds for disabled capacity of stdlib
-		#ifdef _GLIBCXX_HAVE_BROKEN_VSWPRINTF
-			#if (__GNUC__ < 5)
-			#	define STD_TO_STRING_NOT_SUPPORTED
-			#endif
-
-			#define STD_TO_WSTRING_NOT_SUPPORTED
-		#endif
-	#endif
-
-	#if (__GNUC__ == 4)
-		#if ((__GNUC_MINOR__ < 8) || (__GNUC_MINOR__ == 8 && __GNUC_PATCHLEVEL__ < 1))
-			#define STD_THREAD_NOT_SUPPORTED
-
-			//boost.thread is preferred
-			//but if USE_github_com_meganz_mingw_std_threads is enabled,
-			//boost.thread will be replaced with meganz's mingw-std-threads.
-			// https://github.com/meganz/mingw-std-threads
-			#if !defined( USE_github_com_meganz_mingw_std_threads )
-				//#define USE_github_com_meganz_mingw_std_threads
-			#endif
-		#endif
-
-		#if (__GNUC_MINOR__ < 9)
-			#define STD_MAKE_UNIQUE_NOT_SUPPORTED
-		#endif
-
-		#if defined(NANA_MINGW)
-			//It's a knonwn issue under MinGW
-			#define STD_NUMERIC_CONVERSIONS_NOT_SUPPORTED
-		#endif
-
-		#if (__GNUC_MINOR__ < 8)
-			//introduce to_string/to_wstring workaround for lack of stdlib definitions
-			#ifndef STD_TO_STRING_NOT_SUPPORTED
-			#	define STD_TO_STRING_NOT_SUPPORTED
-			#endif
-
-			#ifndef STD_TO_WSTRING_NOT_SUPPORTED
-			#	define STD_TO_WSTRING_NOT_SUPPORTED
-			#endif
-		#endif
-	#endif
-#endif
-
-
-
-// End compilers ...
-
+#include "c++defines.hpp"
 
 // Here defines some flags that tell Nana what features will be supported.
 
@@ -199,29 +48,4 @@
 #endif
 
 
-
-// always define NANA_UNICODE ?? it will be deprecated ?.
-#ifndef NANA_UNICODE
-	#define NANA_UNICODE
-#endif
-
-#if defined(NANA_UNICODE) && defined(NANA_WINDOWS)
-	#ifndef _UNICODE
-		#define _UNICODE
-	#endif
-
-	#ifndef UNICODE
-		#define UNICODE
-	#endif
-#endif
-
-#if !defined(VERBOSE_PREPROCESSOR)
-    //#define VERBOSE_PREPROCESSOR
-#endif
-
-#if !defined(STOP_VERBOSE_PREPROCESSOR)
-	#define STOP_VERBOSE_PREPROCESSOR
-#endif
-
-
 #endif  // NANA_CONFIG_HPP