diff --git a/hgsane/sane_hg_mdw.h b/hgsane/sane_hg_mdw.h
index b754b11..7f3fe16 100644
--- a/hgsane/sane_hg_mdw.h
+++ b/hgsane/sane_hg_mdw.h
@@ -71,7 +71,6 @@ class hg_sane_middleware
 	static void device_pnp(int sig);	// 热插拔事件监控
 	static SANE_Fixed double_2_sane_fixed(double v);
 	static double sane_fixed_2_double(SANE_Fixed v);
-	static std::string option_value_2_string(SANE_Value_Type type, void* val);
 
 	void on_device_closed(scanner_handle h);
 	SANE_Status open(SANE_String_Const devicename, SANE_Handle* handle, const char* name, const char* pwd, const char* method, char* rsc);
@@ -165,6 +164,7 @@ public:
 	static hg_sane_middleware* instance(void);
 	static void set_callback(sane_callback cb, void* param);
 	static void clear(void);
+	static std::string option_value_2_string(SANE_Value_Type type, void* val);
 	static scanner_handle sane_handle_to_scanner(SANE_Handle h);
 	static SANE_Handle scanner_handle_to_sane(scanner_handle h);
 	static SANE_Option_Descriptor* string_option_to_SANE_descriptor(const char* name, const char* title, const char* desc