diff --git a/ndn-cpp/common.hpp b/ndn-cpp/common.hpp
index e477687..f82a77e 100644
--- a/ndn-cpp/common.hpp
+++ b/ndn-cpp/common.hpp
@@ -41,7 +41,14 @@
   if (value)
     vec.insert(vec.begin(), value, value + valueLength);  
 }
-  
+ 
+/**
+ * Return the hex representation of the bytes in array.
+ * @param array The array of bytes.
+ * @return Hex string.
+ */
+std::string toHex(const std::vector<unsigned char> &array);
+
 }
 
 #endif