diff --git a/include/nana/deploy.hpp b/include/nana/deploy.hpp
index 9b8cf203..088f8be5 100644
--- a/include/nana/deploy.hpp
+++ b/include/nana/deploy.hpp
@@ -81,6 +81,35 @@ namespace nana
 
 	std::wstring utf8_cast(const std::string&);
 	std::string utf8_cast(const std::wstring&);
+
+	const std::string& to_utf8(const std::string&);
+	std::string to_utf8(const std::wstring&);
+
+	std::wstring to_wstring(const std::string& utf8_str);
+	const std::wstring& to_wstring(const std::wstring& wstr);
+	std::wstring&& to_wstring(std::wstring&& wstr);
+
+
+	namespace detail
+	{
+#if defined(NANA_WINDOWS)
+		using native_string_type = std::wstring;
+#else	//POSIX
+		using native_string_type = std::string;
+#endif
+	}
+
+#if defined(NANA_WINDOWS)
+	const detail::native_string_type to_native_string(const std::string&);
+	const detail::native_string_type& to_native_string(const std::wstring&);
+	detail::native_string_type to_native_string(int);
+	detail::native_string_type to_native_string(double);
+#else	//POSIX
+	const detail::native_string_type& to_native_string(const std::string&);
+	const detail::native_string_type to_native_string(const std::wstring&);
+	detail::native_string_type to_native_string(int);
+	detail::native_string_type to_native_string(double);
+#endif
 }
 
 #ifndef NANA_UNICODE
diff --git a/include/nana/gui/detail/basic_window.hpp b/include/nana/gui/detail/basic_window.hpp
index b725b6bb..207f7e3b 100644
--- a/include/nana/gui/detail/basic_window.hpp
+++ b/include/nana/gui/detail/basic_window.hpp
@@ -145,7 +145,7 @@ namespace detail
 		basic_window	*parent;
 		basic_window	*owner;
 
-		::std::string	title;
+		native_string_type		title;
 		::nana::detail::drawer	drawer;	//Self Drawer with owen graphics
 		basic_window*		root_widget;	//A pointer refers to the root basic window, if the window is a root, the pointer refers to itself.
 		paint::graphics*	root_graph;		//Refer to the root buffer graphics
diff --git a/include/nana/gui/detail/native_window_interface.hpp b/include/nana/gui/detail/native_window_interface.hpp
index 186d3e68..4ad3d1d0 100644
--- a/include/nana/gui/detail/native_window_interface.hpp
+++ b/include/nana/gui/detail/native_window_interface.hpp
@@ -34,6 +34,8 @@ namespace detail
 			unsigned extra_height;	//extra border size, it is useful in Windows, ignore in X11 always 0
 		};
 
+		using native_string_type = ::nana::detail::native_string_type;
+
 		static nana::size	primary_monitor_size();
 		static rectangle screen_area_from_point(const point&);
 		static window_result create_window(native_window_type, bool nested, const rectangle&, const appearance&);
@@ -65,8 +67,8 @@ namespace detail
 
 		static void	window_size(native_window_type, const size&);
 		static void	get_window_rect(native_window_type, rectangle&);
-		static void	window_caption(native_window_type, const std::string&);
-		static std::string	window_caption(native_window_type);
+		static void	window_caption(native_window_type, const native_string_type&);
+		static native_string_type	window_caption(native_window_type);
 		static void	capture_window(native_window_type, bool);
 		static nana::point	cursor_position();
 		static native_window_type get_owner_window(native_window_type);
diff --git a/include/nana/gui/detail/widget_notifier_interface.hpp b/include/nana/gui/detail/widget_notifier_interface.hpp
index 8439304d..81a0a28f 100644
--- a/include/nana/gui/detail/widget_notifier_interface.hpp
+++ b/include/nana/gui/detail/widget_notifier_interface.hpp
@@ -30,8 +30,8 @@ namespace nana
 
 			virtual widget* widget_ptr() const = 0;
 			virtual void destroy() = 0;
-			virtual std::string caption() = 0;
-			virtual void caption(std::string) = 0;
+			virtual ::nana::detail::native_string_type caption() = 0;
+			virtual void caption(::nana::detail::native_string_type) = 0;
 		};
 	}
 }
diff --git a/include/nana/gui/programming_interface.hpp b/include/nana/gui/programming_interface.hpp
index 0612f664..dfa4e610 100644
--- a/include/nana/gui/programming_interface.hpp
+++ b/include/nana/gui/programming_interface.hpp
@@ -72,8 +72,8 @@ namespace API
 		widget_colors* get_scheme(window);
 
 		void attach_drawer(widget&, drawer_trigger&);
-		std::string window_caption(window) throw();
-		void window_caption(window, std::string);
+		::nana::detail::native_string_type window_caption(window) throw();
+		void window_caption(window, ::nana::detail::native_string_type);
 
 		window create_window(window, bool nested, const rectangle&, const appearance&, widget* attached);
 		window create_widget(window, const rectangle&, widget* attached);
@@ -271,7 +271,7 @@ namespace API
 	void update_window(window);            ///< Copies the off-screen buffer to the screen for immediate display.
 
 	void window_caption(window, const std::string& title_utf8);
-	void window_caption(window, const nana::string& title);
+	void window_caption(window, const std::wstring& title);
 	::std::string window_caption(window);
 
 	void window_cursor(window, cursor);
diff --git a/include/nana/gui/widgets/button.hpp b/include/nana/gui/widgets/button.hpp
index 955de3a3..cce1abe1 100644
--- a/include/nana/gui/widgets/button.hpp
+++ b/include/nana/gui/widgets/button.hpp
@@ -104,7 +104,7 @@ namespace nana{
 		private:
 			//Overrides widget virtual functions
 			void _m_complete_creation() override;
-			void _m_caption(std::string&&) override;
+			void _m_caption(native_string_type&&) override;
 		};
 }//end namespace nana
 #endif
diff --git a/include/nana/gui/widgets/categorize.hpp b/include/nana/gui/widgets/categorize.hpp
index 6d685e8c..1e97d1f5 100644
--- a/include/nana/gui/widgets/categorize.hpp
+++ b/include/nana/gui/widgets/categorize.hpp
@@ -238,10 +238,10 @@ namespace nana
 		}
 	private:
 		//Overrides widget's virtual functions
-		void _m_caption(std::string&& str) override
+		void _m_caption(native_string_type&& str) override
 		{
-			this->get_drawer_trigger().path(str);
-			API::dev::window_caption(*this, this->get_drawer_trigger().path());
+			this->get_drawer_trigger().path(to_utf8(str));
+			API::dev::window_caption(*this, to_native_string(this->get_drawer_trigger().path()) );
 		}
 	};
 }//end namespace nana
diff --git a/include/nana/gui/widgets/combox.hpp b/include/nana/gui/widgets/combox.hpp
index 3297ee18..c3033a9c 100644
--- a/include/nana/gui/widgets/combox.hpp
+++ b/include/nana/gui/widgets/combox.hpp
@@ -223,8 +223,8 @@ namespace nana
 		const drawerbase::combox::drawer_impl& _m_impl() const;
 	private:
 		//Overrides widget's virtual functions
-		::std::string _m_caption() const throw() override;
-		void _m_caption(::std::string&&) override;
+		native_string_type _m_caption() const throw() override;
+		void _m_caption(native_string_type&&) override;
 		nana::any * _m_anyobj(std::size_t pos, bool alloc_if_empty) const override;
 	};
 }
diff --git a/include/nana/gui/widgets/group.hpp b/include/nana/gui/widgets/group.hpp
index d05a7525..79162f06 100644
--- a/include/nana/gui/widgets/group.hpp
+++ b/include/nana/gui/widgets/group.hpp
@@ -77,8 +77,8 @@ namespace nana{
 		void _m_add_child(const char* field, widget*);
 		void _m_init();
 		void _m_complete_creation() override;
-		::std::string _m_caption() const throw() override;
-		void _m_caption(::std::string&&) override;
+		native_string_type _m_caption() const throw() override;
+		void _m_caption(native_string_type&&) override;
 	private:
 		std::unique_ptr<implement> impl_;
     };
diff --git a/include/nana/gui/widgets/label.hpp b/include/nana/gui/widgets/label.hpp
index 7f769f27..f7071914 100644
--- a/include/nana/gui/widgets/label.hpp
+++ b/include/nana/gui/widgets/label.hpp
@@ -76,7 +76,7 @@ namespace nana
 		label& text_align(align horizontal_align, align_v vertical_align= align_v::top);
 	private:
 		//Overrides widget's virtual function
-		void _m_caption(std::string&&) override;
+		void _m_caption(native_string_type&&) override;
 	};
 }//end namespace nana
 #endif
diff --git a/include/nana/gui/widgets/spinbox.hpp b/include/nana/gui/widgets/spinbox.hpp
index 00fab1d9..4bc85000 100644
--- a/include/nana/gui/widgets/spinbox.hpp
+++ b/include/nana/gui/widgets/spinbox.hpp
@@ -106,8 +106,8 @@ namespace nana
 		void modifier(std::wstring prefix, std::wstring suffix);
 		void modifier(const std::string & prefix_utf8, const std::string& suffix_utf8);
 	private:
-		::std::string _m_caption() const throw();
-		void _m_caption(::std::string&&);
+		native_string_type _m_caption() const throw();
+		void _m_caption(native_string_type&&);
 	}; //end class spinbox
 }//end namespace nana
 
diff --git a/include/nana/gui/widgets/textbox.hpp b/include/nana/gui/widgets/textbox.hpp
index 9d2d70bc..65c37522 100644
--- a/include/nana/gui/widgets/textbox.hpp
+++ b/include/nana/gui/widgets/textbox.hpp
@@ -209,8 +209,8 @@ namespace nana
 		unsigned line_pixels() const;
 	protected:
 		//Overrides widget's virtual functions
-		::std::string _m_caption() const throw() override;
-		void _m_caption(::std::string&&) override;
+		native_string_type _m_caption() const throw() override;
+		void _m_caption(native_string_type&&) override;
 		void _m_typeface(const paint::font&) override;
 	};
 }//end namespace nana
diff --git a/include/nana/gui/widgets/widget.hpp b/include/nana/gui/widgets/widget.hpp
index 4dde5a06..b8304031 100644
--- a/include/nana/gui/widgets/widget.hpp
+++ b/include/nana/gui/widgets/widget.hpp
@@ -34,11 +34,8 @@ namespace nana
 		class inner_widget_notifier;
 		typedef void(*dummy_bool_type)(widget* (*)(const widget&));
 	public:
-#if defined(NANA_WINDOWS)
-		using native_string_type = std::wstring;
-#else	//POSIX
-		using native_string_type = std::string;
-#endif
+		using native_string_type = detail::native_string_type;
+
 		virtual ~widget() = default;
 		virtual window handle() const = 0;			///< Returns the handle of window, returns 0 if window is not created.
 		bool empty() const;							///< Determines whether the manipulator is handling a window.
@@ -113,8 +110,8 @@ namespace nana
 		virtual void _m_complete_creation();
 
 		virtual general_events& _m_get_general_events() const = 0;
-		virtual ::std::string _m_caption() const throw();
-		virtual void _m_caption(::std::string&&);
+		virtual native_string_type _m_caption() const throw();
+		virtual void _m_caption(native_string_type&&);
 		virtual nana::cursor _m_cursor() const;
 		virtual void _m_cursor(nana::cursor);
 		virtual void _m_close();
diff --git a/source/deploy.cpp b/source/deploy.cpp
index 1c8fd611..3c3b540d 100644
--- a/source/deploy.cpp
+++ b/source/deploy.cpp
@@ -407,6 +407,73 @@ namespace nana
 		return ::nana::charset(text).to_bytes(::nana::unicode::utf8);
 	}
 
+	const std::string& to_utf8(const std::string& str)
+	{
+		return str;
+	}
+
+	std::string to_utf8(const std::wstring& text)
+	{
+		return ::nana::charset(text).to_bytes(::nana::unicode::utf8);
+	}
+
+	std::wstring to_wstring(const std::string& utf8_str)
+	{
+		return ::nana::charset(utf8_str, ::nana::unicode::utf8);
+	}
+
+	const std::wstring& to_wstring(const std::wstring& wstr)
+	{
+		return wstr;
+	}
+
+	std::wstring&& to_wstring(std::wstring&& wstr)
+	{
+		return static_cast<std::wstring&&>(wstr);
+	}
+
+#if defined(NANA_WINDOWS)
+	const detail::native_string_type to_native_string(const std::string& text)
+	{
+		return ::nana::charset(text, ::nana::unicode::utf8);
+	}
+
+	const detail::native_string_type& to_native_string(const std::wstring& text)
+	{
+		return text;
+	}
+
+	detail::native_string_type to_native_string(int n)
+	{
+		return std::to_wstring(n);
+	}
+
+	detail::native_string_type to_native_string(double d)
+	{
+		return std::to_wstring(d);
+	}
+#else	//POSIX
+	const detail::native_string_type& to_native_string(const std::string& text)
+	{
+		return text;
+	}
+
+	const detail::native_string_type to_native_string(const std::wstring& text)
+	{
+		return ::nana::charset(text).to_bytes(::nana::unicode::utf8);
+	}
+
+	detail::native_string_type to_native_string(int n)
+	{
+		return std::to_string(n);
+	}
+
+	detail::native_string_type to_native_string(double d)
+	{
+		return std::to_string(d);
+	}
+#endif
+
 
 	std::size_t strlen(const char_t* str)
 	{
diff --git a/source/gui/detail/native_window_interface.cpp b/source/gui/detail/native_window_interface.cpp
index e97b318b..8fbcabe1 100644
--- a/source/gui/detail/native_window_interface.cpp
+++ b/source/gui/detail/native_window_interface.cpp
@@ -1076,18 +1076,17 @@ namespace nana{
 #endif
 		}
 
-		void native_interface::window_caption(native_window_type wd, const std::string& title)
+		void native_interface::window_caption(native_window_type wd, const native_string_type& title)
 		{
 #if defined(NANA_WINDOWS)
-			std::wstring wtext = ::nana::charset(title, ::nana::unicode::utf8);
 			if(::GetCurrentThreadId() != ::GetWindowThreadProcessId(reinterpret_cast<HWND>(wd), 0))
 			{
-				wchar_t * wstr = new wchar_t[wtext.length() + 1];
-				std::wcscpy(wstr, wtext.c_str());
+				wchar_t * wstr = new wchar_t[title.length() + 1];
+				std::wcscpy(wstr, title.c_str());
 				::PostMessage(reinterpret_cast<HWND>(wd), nana::detail::messages::remote_thread_set_window_text, reinterpret_cast<WPARAM>(wstr), 0);
 			}
 			else
-				::SetWindowText(reinterpret_cast<HWND>(wd), wtext.c_str());
+				::SetWindowText(reinterpret_cast<HWND>(wd), title.c_str());
 #elif defined(NANA_X11)
 			::XTextProperty name;
 			char * text = const_cast<char*>(title.c_str());
@@ -1101,13 +1100,13 @@ namespace nana{
 #endif
 		}
 
-		std::string native_interface::window_caption(native_window_type wd)
+		auto native_interface::window_caption(native_window_type wd) -> native_string_type
 		{
 #if defined(NANA_WINDOWS)
 			int length = ::GetWindowTextLength(reinterpret_cast<HWND>(wd));
 			if(length > 0)
 			{
-				nana::string str;
+				native_string_type str;
                 //One for NULL terminator which GetWindowText will write.
 				str.resize(length+1);
 				
@@ -1116,7 +1115,7 @@ namespace nana{
 				//Remove the null terminator writtien by GetWindowText
 				str.resize(length);
 
-				return ::nana::charset(str);
+				return str;
 			}
 #elif defined(NANA_X11)
 			nana::detail::platform_scope_guard psg;
@@ -1136,7 +1135,7 @@ namespace nana{
 				}
 			}
 #endif
-			return std::string();
+			return native_string_type();
 		}
 
 		void native_interface::capture_window(native_window_type wd, bool cap)
diff --git a/source/gui/programming_interface.cpp b/source/gui/programming_interface.cpp
index 97daa458..6f76bcbc 100644
--- a/source/gui/programming_interface.cpp
+++ b/source/gui/programming_interface.cpp
@@ -220,7 +220,7 @@ namespace API
 			}
 		}
 
-		std::string window_caption(window wd) throw()
+		::nana::detail::native_string_type window_caption(window wd) throw()
 		{
 			auto const iwd = reinterpret_cast<basic_window*>(wd);
 			internal_scope_guard isg;
@@ -234,7 +234,7 @@ namespace API
 			return {};
 		}
 
-		void window_caption(window wd, std::string title)
+		void window_caption(window wd, ::nana::detail::native_string_type title)
 		{
 			auto const iwd = reinterpret_cast<basic_window*>(wd);
 			internal_scope_guard lock;
@@ -823,12 +823,15 @@ namespace API
 		auto const iwd = reinterpret_cast<basic_window*>(wd);
 		internal_scope_guard lock;
 		if (restrict::wd_manager().available(iwd))
-			iwd->widget_notifier->caption(title_utf8);
+			iwd->widget_notifier->caption(to_native_string(title_utf8));
 	}
 
-	void window_caption(window wd, const nana::string& title)
+	void window_caption(window wd, const std::wstring& title)
 	{
-		window_caption(wd, static_cast<std::string>(::nana::charset(title).to_bytes(::nana::unicode::utf8)));
+		auto const iwd = reinterpret_cast<basic_window*>(wd);
+		internal_scope_guard lock;
+		if (restrict::wd_manager().available(iwd))
+			iwd->widget_notifier->caption(to_native_string(title));
 	}
 
 	std::string window_caption(window wd)
@@ -836,7 +839,7 @@ namespace API
 		auto const iwd = reinterpret_cast<basic_window*>(wd);
 		internal_scope_guard lock;
 		if (restrict::wd_manager().available(iwd))
-			return iwd->widget_notifier->caption();
+			return to_utf8(iwd->widget_notifier->caption());
 
 		return{};
 	}
diff --git a/source/gui/widgets/button.cpp b/source/gui/widgets/button.cpp
index 703bf7d9..61c3f082 100644
--- a/source/gui/widgets/button.cpp
+++ b/source/gui/widgets/button.cpp
@@ -511,11 +511,11 @@ namespace nana{	namespace drawerbase
 				});
 			}
 
-			void button::_m_caption(std::string&& text)
+			void button::_m_caption(native_string_type&& text)
 			{
 				API::unregister_shortkey(handle());
 
-				std::wstring wtext = ::nana::charset(text, ::nana::unicode::utf8);
+				std::wstring wtext = ::nana::to_wstring(text);
 
 				wchar_t shortkey;
 				API::transform_shortkey_text(wtext, shortkey, 0);
diff --git a/source/gui/widgets/categorize.cpp b/source/gui/widgets/categorize.cpp
index 135087a9..87075b69 100644
--- a/source/gui/widgets/categorize.cpp
+++ b/source/gui/widgets/categorize.cpp
@@ -543,7 +543,7 @@ namespace nana
 				{
 					if(node)
 					{
-						API::dev::window_caption(window_handle(), tree().path());
+						API::dev::window_caption(window_handle(), to_native_string(tree().path()));
 						if(evt_holder_.selected)
 							evt_holder_.selected(node->value.second.value);
 					}
@@ -807,7 +807,7 @@ namespace nana
 				{
 					throw_not_utf8(str);
 					scheme_->tree().insert(str, value);
-					API::dev::window_caption(scheme_->window_handle(), scheme_->tree().path());
+					API::dev::window_caption(scheme_->window_handle(), to_native_string(scheme_->tree().path()));
 					scheme_->draw();
 				}
 
diff --git a/source/gui/widgets/combox.cpp b/source/gui/widgets/combox.cpp
index 471ca968..ad1fa88c 100644
--- a/source/gui/widgets/combox.cpp
+++ b/source/gui/widgets/combox.cpp
@@ -982,22 +982,22 @@ namespace nana
 				API::refresh_window(*this);
 		}
 
-		std::string combox::_m_caption() const throw()
+		auto combox::_m_caption() const throw() -> native_string_type
 		{
 			internal_scope_guard lock;
 			auto editor = _m_impl().editor();
 			if (editor)
-				return ::nana::charset(editor->text());
-			return std::string();
+				return to_native_string(editor->text());
+			return native_string_type();
 		}
 
-		void combox::_m_caption(std::string&& str)
+		void combox::_m_caption(native_string_type&& str)
 		{
 			internal_scope_guard lock;
 
 			auto editor = _m_impl().editor();
 			if (editor)
-				editor->text(::nana::charset(str, nana::unicode::utf8));
+				editor->text(to_native_string(str));
 
 			API::refresh_window(*this);
 		}
diff --git a/source/gui/widgets/group.cpp b/source/gui/widgets/group.cpp
index a7f4418a..aa4d3346 100644
--- a/source/gui/widgets/group.cpp
+++ b/source/gui/widgets/group.cpp
@@ -234,12 +234,12 @@ namespace nana{
 		_m_init();
 	}
 
-	::std::string group::_m_caption() const throw()
+	auto group::_m_caption() const throw() -> native_string_type
 	{
-		return impl_->caption.caption();
+		return impl_->caption.caption_native();
 	}
 
-	void group::_m_caption(::std::string&& str)
+	void group::_m_caption(native_string_type&& str)
 	{
 		impl_->caption.caption(std::move(str));
 		impl_->update_div();
diff --git a/source/gui/widgets/label.cpp b/source/gui/widgets/label.cpp
index a8b700f1..f6968dd0 100644
--- a/source/gui/widgets/label.cpp
+++ b/source/gui/widgets/label.cpp
@@ -807,7 +807,7 @@ namespace nana
 			if(impl->renderer.format(f))
 			{
 				window wd = *this;
-				impl->renderer.parse(::nana::charset(API::dev::window_caption(wd), ::nana::unicode::utf8));
+				impl->renderer.parse(::nana::to_wstring(API::dev::window_caption(wd)));
 				API::refresh_window(wd);
 			}
 			return *this;
@@ -869,11 +869,11 @@ namespace nana
 			return *this;
 		}
 
-		void label::_m_caption(std::string&& str)
+		void label::_m_caption(native_string_type&& str)
 		{
 			internal_scope_guard lock;
 			window wd = *this;
-			get_drawer_trigger().impl()->renderer.parse(::nana::charset(str, nana::unicode::utf8));
+			get_drawer_trigger().impl()->renderer.parse(to_wstring(str));
 			API::dev::window_caption(wd, std::move(str));
 			API::refresh_window(wd);
 		}
diff --git a/source/gui/widgets/spinbox.cpp b/source/gui/widgets/spinbox.cpp
index c8787785..bd1c15fc 100644
--- a/source/gui/widgets/spinbox.cpp
+++ b/source/gui/widgets/spinbox.cpp
@@ -677,22 +677,22 @@ namespace nana
 		modifier(static_cast<std::wstring>(::nana::charset(prefix_utf8, ::nana::unicode::utf8)), static_cast<std::wstring>(::nana::charset(suffix_utf8, ::nana::unicode::utf8)));
 	}
 
-	::std::string spinbox::_m_caption() const throw()
+	auto spinbox::_m_caption() const throw() -> native_string_type
 	{
 		internal_scope_guard lock;
 		auto editor = get_drawer_trigger().impl()->editor();
 		if (editor)
-			return ::nana::charset(editor->text());
-		return std::string();
+			return to_native_string(editor->text());
+		return native_string_type();
 	}
 
-	void spinbox::_m_caption(::std::string&& text)
+	void spinbox::_m_caption(native_string_type&& text)
 	{
 		internal_scope_guard lock;
 		auto editor = get_drawer_trigger().impl()->editor();
 		if (editor)
 		{
-			editor->text(::nana::charset(text, ::nana::unicode::utf8));
+			editor->text(to_wstring(text));
 			API::refresh_window(*this);
 		}
 	}
diff --git a/source/gui/widgets/textbox.cpp b/source/gui/widgets/textbox.cpp
index b7a6688d..26e588b7 100644
--- a/source/gui/widgets/textbox.cpp
+++ b/source/gui/widgets/textbox.cpp
@@ -492,7 +492,7 @@ namespace drawerbase {
 
 			std::stringstream ss;
 			int value;
-			ss << s;
+			ss << to_utf8(s);
 			ss >> value;
 			return value;
 		}
@@ -504,20 +504,20 @@ namespace drawerbase {
 
 			std::stringstream ss;
 			double value;
-			ss << s;
+			ss << to_utf8(s);
 			ss >> value;
 			return value;
 		}
 
 		textbox& textbox::from(int n)
 		{
-			_m_caption(std::to_string(n));
+			_m_caption(to_native_string(n));
 			return *this;
 		}
 
 		textbox& textbox::from(double d)
 		{
-			_m_caption(std::to_string(d));
+			_m_caption(to_native_string(d));
 			return *this;
 		}
 
@@ -595,23 +595,23 @@ namespace drawerbase {
 		}
 
 		//Override _m_caption for caption()
-		::std::string textbox::_m_caption() const throw()
+		auto textbox::_m_caption() const throw() -> native_string_type
 		{
 			internal_scope_guard lock;
 			auto editor = get_drawer_trigger().editor();
 			if (editor)
-				return ::nana::charset(editor->text());
+				return to_native_string(editor->text());
 
-			return std::string();
+			return native_string_type();
 		}
 
-		void textbox::_m_caption(std::string&& str)
+		void textbox::_m_caption(native_string_type&& str)
 		{
 			internal_scope_guard lock;
 			auto editor = get_drawer_trigger().editor();
 			if (editor)
 			{
-				editor->text(::nana::charset(str, ::nana::unicode::utf8));
+				editor->text(to_wstring(str));
 				API::update_window(this->handle());
 			}
 		}
diff --git a/source/gui/widgets/widget.cpp b/source/gui/widgets/widget.cpp
index 3d180aed..a98bc289 100644
--- a/source/gui/widgets/widget.cpp
+++ b/source/gui/widgets/widget.cpp
@@ -41,12 +41,12 @@ namespace nana
 				wdg_._m_notify_destroy();
 			}
 
-			std::string caption() override
+			native_string_type caption() override
 			{
 				return wdg_._m_caption();
 			}
 
-			virtual void caption(std::string text)
+			void caption(native_string_type text) override
 			{
 				wdg_._m_caption(std::move(text));
 			}
@@ -56,33 +56,35 @@ namespace nana
 
 		std::string widget::caption() const throw()
 		{
-			return this->_m_caption();
+			return utf8_cast(_m_caption());
 		}
 
 		std::wstring widget::caption_wstring() const throw()
 		{
+#if defined(NANA_WINDOWS)
+			return _m_caption();
+#else
 			return utf8_cast(_m_caption());
+#endif
 		}
 
 		auto widget::caption_native() const throw() -> native_string_type
 		{
-#if defined(NANA_WINDOWS)
-			return caption_wstring();
-#else
-			return caption();
-#endif
+			return _m_caption();
 		}
 
 		widget& widget::caption(std::string utf8)
 		{
 			::nana::throw_not_utf8(utf8);
-			_m_caption(std::move(utf8));
+			native_string_type str = to_native_string(utf8);
+			_m_caption(std::move(str));
 			return *this;
 		}
 
 		widget& widget::caption(std::wstring text)
 		{
-			_m_caption(utf8_cast(text));
+			native_string_type str = to_native_string(text);
+			_m_caption(std::move(str));
 			return *this;
 		}
 
@@ -90,7 +92,8 @@ namespace nana
 		{
 			if (handle())
 			{
-				_m_caption(eval());
+				native_string_type str = to_native_string(eval());
+				_m_caption(std::move(str));
 				internationalization_parts::set_eval(handle(), std::move(eval));
 			}
 		}
@@ -269,12 +272,12 @@ namespace nana
 		void widget::_m_complete_creation()
 		{}
 
-		std::string widget::_m_caption() const throw()
+		auto widget::_m_caption() const throw() -> native_string_type
 		{
 			return API::dev::window_caption(handle());
 		}
 
-		void widget::_m_caption(std::string&& str)
+		void widget::_m_caption(native_string_type&& str)
 		{
 			API::dev::window_caption(handle(), std::move(str));
 		}